Solid Rocket Thrust Vector Contro Nasa Lsp8114

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FOREWORD

NASA experience has indicated a need Accordingly, criteria are being developed

for uniform criteria for the design of space in the following areas of technology:

vehicles.

Environment Structures

Individual components are completed. This

of this document,

Guidance

and Control

Chemical

Propulsion

work will be issued as separate monographs as soon as they part of the series on Chemical Propulsion, is one such

monograph. A list of all monographs of this document. These except

monographs as may be

these

documents,

unifqrm This

design

of Howard management

are to be regarded specified in formal revised

practices

monograph,

issued

"Solid

Rocket

W. Douglass, Chief, was by M. Murray

to this one

can be found

on the

as guides to design and not as NASA project specifications. It is expected,

as experience for NASA

prior

may

space

indicate

to be desirable,

final

pages

requirements, however, that

eventually

will provide

vehicles.

Thrust

Vector

Design Bailey.

Control,"

Criteria Office, The monograph

was prepared Lewis was

under

the direction

Research Center; written by Robert

project F. H.

Woodberry and Richard J. Zeamer of Hercules, Inc., and was edited by Russell B. Keller, Jr. of Lewis. To assure technical accuracy of this document, scientists and engineers throughout the technical community participated in interviews, consultations, and critical review of the text.

In

particular,

Thomas

S. Clark

Aircraft Corporation; Lionel H. Erickson of Aerojet Solid Propulsion Company; Center reviewed the monograph in detail. Comments National Office), December

concerning Aeronautics Cleveland, 1974

Ohio

the and

of

United

of Thiokol and James

Technology Chemical J. Pelouch,

Center,

Corporation;Myron Jr. of the Lewis

technical content of this monograph Space Administration, Lewis Research

44135.

Division

will be welcomed Center (Design

of United Morgan Research

by the Criteria

For sale by the National Technical Springfield, Virginia 22161 Price - $7.00

Information

Service

GUIDE

The

purpose

significant programs

of this

is to organize

and

present,

accumulated current design

for effective

that

The

the

of which

are

Art,

design

preceded

by

section

2,

elements

a brief

reviews

introduction

and

are involved

discusses

in successful

use

in design,

the

in development and operational practices, and from them establishes

for achieving greater consistency in design, increased greater efficiency in the design effort. The monograph

major sections references. State

monograph

experience and knowledge to date. It reviews and assesses

firm guidance product, and

identifies

TO THE USE OF THIS MONOGRAPH

reliability is organized

and

complemented

the

total

design.

current technology pertaining to these elements. When detailed best available references are cited. This section serves as a survey background material and prepares a proper technological base Recommended Practices.

design

It describes

in the end into two by

a set

of

problem,

and

succinctly

the

information is required, the of the subject that provides for the Design Criteria and

The Design Criteria, shown in italics in section 3, state clearly and briefly wha.._.__t rule, guide, limitation, or standard must be imposed on each essential_ design element to assure successful design. The Design Criteria can serve effectively as a checklist of rules for the project manager to use in guiding a design or in assessing its adequacy. The

Recommended

Whenever appropriate

Practices,

also

in section

3, state

Design Criteria, successful design.

provide

positive

guidance

to

Both sections have been organized into decimally within similarly numbered subsections correspond the Contents displays design can be followed The design specifications,

how

to satisfy

each

of the

possible, the best procedure is described; when this cannot be done references are provided. The Recommended Practices, in conjunction

this continuity through both

criteria monograph or a design manual.

loosely organized its merit should to the designer.

body of existing be judged on how

the

practicing

designer

on

how

that

a particular

is not intended to be a design handbook, It is a summary and a systematic ordering of the

nl

to achieve

numbered subsections so that the subjects from section to section. The format for

of subject in such a way sections as a discrete subject.

successful effectively

criteria.

concisely, with the

design techniques and it makes that material

practices. available

aspect

of

a set of large and

Its value and to and useful

CONTENTS

Page

.

INTRODUCTION

2.

STATE

3.

DESIGN

1

............................

OF THE

ART

CRITERIA

and Recommended

Practices

Units to SI Units

APPENDIX

A - Conversion

of U. S. Customary

APPENDIX

B - Glossary

............................

REFERENCES NASA

3

........................ ................

161

............

163 173

................................

Space Vehicle

Design

Criteria

Monographs

Issued

to Date

STATE

SUBJECT

185

.............

OF THE

ART

DESIGN

CRITERIA

2.1

18

3.1

117

Configuration Design Optimization Envelope Limitations

2.1.1 2.1.1.1 2.1.1.2

18 21 22

3.1.1 3.1.1.1 3.1.1.2

117 117 118

Design Requirements Actuation Torque

2.1.2 2.1.2.1

22 23

3.1.2 _1.2.1

119

2.1.2.1.1 2.1.2.1.2 2.1.2.1.3

24 26 27

_1.2.1.1 3.1.2.1.2 3.1.2.1.3

2.1.2.1.4 2.1.2.1.5

29 29

3.1.2.1.4 3.1.2.1.5

120 120 121

2.1.2.1.6 2.1.2.1.7

29 30

3.1.2.1.6 3.1.2.1.7

121 121

2.1.2.1.8 2.1.2.2

30 31

3.1.2.1.8 _1.2.2

122 122

2.1.2.3 2.1.2.3.1

33 35

_1.2.3 3.1.2.._1

123 123

2.1.2.4 2.1.2.5 2.1.2.5.1

36 37 37

3.1.2.4 _1.2.5 _1.2.5.1

124 125 125

2.1.2.5.2 2.1.2.6

39 40

_1.2.5.2 3.1.2.6

125

FLEXIBLE

JOINT

Joint Spring Torque Friction Torque Offset Torque Inertial Torque Gravitational Torque Insulating-Boot Torque Internal Aerodynamic Torque External Aerodynamic Torque Nozzle Vector Angle Axial Deflection Nozzle

and Pivot

Misalignment

Frequency Response Environmental Protection Thermal Protection Aging Pressure

Protection Sealing

Point

119 119 120

126

SUBJECT

Material

STATE OF THE ART

Selection

Elastomers Reinforcements Adhesive Bond System Joint Thermal Protection Mechanical General

Design Considerations

Design Definitions Design Safety Factor Flexible-Joint Loads Structural Analysis Elastomer Thickness Reinforcement Thickness Advanced

Analysis

Manufacture Reinforcements Joint Adhesive Flexible Joint

System

Testing Subscale Test Program Bench Test Program Static-Firing Destructive Aging

Program

Inspection Inspection Inspection LIQUID

Plan Processes

INJECTION

CONTROL

Program Testing

THRUST

CRITERIA

2.1.3

40

3.1.3

126

2.1.3.1

41

3.1.3.1

126

2.1.3.2 2.1.3.3 2.1.3.4

42 44 44

3.1.3.2 3.1,3.3 3.1.3.4

129 129 130

2.1.4

45

3.1.4

130

2.1.4.1 2.1.4.1.1 2.1.4.2

45 46 47

3.1.4.1

130

3.1.4.2

131

2.1.4.3

47

3.1.4.3

131

2.1.5

48

3.1.5

132

2.1.5.1 2.1.5.2 2.1.5.3

48 51 54

3.1.5.1 3.1.5.2 3.1.5.3

132 133 133

2.1.6

55

3.1.6

134

2.1.6.1 2.1.6.2 2.1.6.3

55 58 59

3.1.6.1 3.1.6.2 3.1.6.3

134 135 135

2.1.7

62

2.1.7.1 2.1.7.2 2.1.7.3

62 64 67

3.1.7 3.1.7.1

136 136

3.1.7.2 3.1.7.3

137 139

2.1.7.4 2.1.7.5

68 68

3.1.7.4 3.1.7.5

139 140

2.1.8

68

3.1.8

140

2.1.8.1

69

3.1.8.1

140

2.1.8.2

69

3.1.8.2

141

2.2

70

3.2

t42

2.2.1

74

3.2.1

142

2.2.1.1 2.2.1.2

78 79

3.2.1.1 3.2.1.2

142 144

3.2.1.3

146

3.2.1.4 3.2.1.5 3.2.1.6

147 148 150

VECTOR

(LITVC)

System

DESIGN

Design

System Optimization Selection of Injectant Injection Pressures and Injection Orifices Injector Amount

Location and Discharge Angle of Liquid Injectant Required

2.2.1.3 2.2.1.4 2.2.1.5

81 86 87

Amount

of Pressurization

2.2.1.6

89

Gas Required

vi

SUBJECT

STATE

Component Design Injectors Storage Tank and Bladder

OF THE ART

DESIGN

CRITERIA

2.2.2 2.2.2.1

89 90

3.2.2 3.2.2.1

151 152

2.2.2.2 2.2.2.3 2.2.2.4

95 97 99

3.2.2.2 3.2.2.3 3.2.2.4

153 154 155

2.2.2.5

99

3.2.2.5

155

2.2.2.6

99

3.2.2.6

157

Performance Evaluation and Testing Performance Data for Design Small-Scale Tests

2.2.3 2.2.3.1 2.2.3.2

103 104 115

3.2.3 3.2.3.1

158 158

Full-Scale Development Tests Operating-Capability Tests

2.2.3.3 2.2.3.4

115 115

3.2.3.2 3.2.3.3

159 160

3.2.3.4

160

Pressurization System Liquid Storage Equalization Disposal of Surplus Injectant Adaptation of the Motor for LITVC

vii

LIST OF FIGURES

Title

Figure 1

Classification

2

Gimbal/swivel

3

Gimbal/integral

4

Supersonic-splitline

5

Ball-and-socket

6

Rotatable

7

Flexible-joint

8

Fluid-bearing/roiling-seal

9

Liquid

10

Hot-gas

11

Jet tab TVC systems

12

Flexible

of thrust

control

subsonic-splitline

nozzle

nozzle nozzle

canted

injection

joint

...................

14

Graphical

15

Effect

16

Movement

17

Effect

18

Shear-stress

19

Buckling stress and dimensions

joint

12

......................

14

.......................

15

.....................

15

...........................

16

position

......................

position

location point

related

for metal reinforcements of the reinforcement test specimen

in a flexible-joint

envelope

different

(due to motor factors

20

of friction

on required

for three

19

.....................

of the effects

of axial deflection

shear

11 12

leg mounted

presentation

correction

11

13

nozzle

in vectored

of pivot

.................

...........................

TVC system

of pivot-point

nozzle

11

.........................

in neutral

Flexible

4

........................

nozzle

TVC system,

.................

..........................

nozzle

Quadruple-lap

systems

low-subsonic-splitline

13

20

vector

Page

as a function ....................

ix

28 31

nozzles

on nozzle

to cone angle

.....................

......

...............

flexible-joint

pressure)

nozzle

alignment

...............

.........

34 .......

36 49

of the properties 53 63

Figure

Title

Page

21

Specialfixturefor testingjoint axialdeflection ................

65

22

Fixturefor testingjoint actuationunderpressure................

66

23

Schematic of typicalliquidinjectionTVCsystemandsideforcephenomena .....

71

24

Nozzlepressure distributiondueto injectionof inertinjectant

72

25

Nozzlepressure distributiondueto injectionof reactive injectant

73

26

Basicdesignfeatures in a LITVCsystem ...................

75

27

Schematic of TitanIII ullageblowdownLITVCsystem .............

76

28

LITVCsystem for PolarisA3 secondstage

77

29

Crosssectiondrawingof typicalsingle-orifice injector mountedonnozzlewall .........................

84

..........

3O

Crosssectiondrawingof three-orifice injectormountedonnozzlewall

31

CrosssectiondrawingOfanelectromechanical injectantvalve ............

85

32

Injectorvalveassembly withhydraulic-powered actuator

91

33

Servo-controlled hydraulicpowersystems forvariable-orifice injectors .......

92

34

Erosionaroundinjectorportsin theTitanIII nozzle ..............

101

35

Comparison of small-scale andfull-scale dataoninjectantspecific impulsevsdeflectionangleandsideforce ...................

105

.......

84

36

Comparison of performance of inertandreactive injectants ............

106

37

Effectsofinjectionlocationandangleoninjectantspecificimpulse .......

107

38

Effectof injectantflowrateandinjectionpressure onsideforce ..........

39

Effectof injectionlocationandorientationonsideforcefor differentinjectantflowrates ........................

109

40

Transformation of dataoninjectionpressure vsinjectantspecificimpulse ......

110

41

Effectofnumberof annularorificesonsideforceasa functionof injectantflowrate

111

x

108

Figure

Title

42

Transformation of performance

data

43

Correlation

impulse

44

TWo examples

of acceptable

45

Two

of unacceptable

46

of injectant

examples

Sketch illustrating of effective pivot

47

Recommended

48

Values

49

Relation

50

Typical

for strontium

perchlorate

with key nozzle

unbonded-elastomer unbonded-elastomer

sequence

of thrust

of steps impulse

deflection

port

for determining

for reactive angle

configuration

showing

xi

112

........

114 127

..........

128

determination 138 the optimum liquid

location erosion

.......

...........

conditions

and inert

to injector

injectant

parameters

conditions

factors involved in experimental point ..........................

of side specific

LITVC

specific

Page

LITVC

injectants

system ........

.............

and char patterns

design

143 145 149

........

158

LIST OF TABLES

Table

Title

Page

I

Advantages,

Disadvantages,

and Current Status of Movable Nozzle Systems

II

Advantages,

Disadvantages,

and Current Status of Secondary

III

Advantages,

Disadvantages,

and Current Status of Mechanical

IV

Advantages,

Disadvantages,

and Current Status of Special Systems

V VI VII

VIII IX X

XI XlI XIII

Integral Values 103) for/3 = 15 ° to 13= 60 ° Comparative

Effects of Forward

Details of Reinforcements and Development Motors Advantages

Compatibility and Aqueous

........

of Joint Fabrication

Pivot Point

Processes

of Main Operational

Chief Design Features of Variable-Orifice

°°°

9

32

56 ..........

Liquid Injectants

60 .....

80

114-B2 82

of Liquid Storage Systems on Operational

Xlll

8

10

.........

Injectors on Operational

for Inert and Reactive Injectants

6

25

of Selected Metals and Nonmetals with Freon Strontium Perchlorate ....................

Side Force Composition

Systems

..................

and Aft Geometric

and Characteristics

Chief Design Features

Deflector

Systems

Used in Flexible Joints on Operational ........................

and Disadvantages

Basic Properties

Injection

.....

LITVC Systems LITVC Systems

............

93 96 103

ROCKET

SOLID THRUST

VECTOR

CONTROL

1. INTRODUCTION Most the

vehicles required

used flight

for launching trajectory

spacecraft

require

will be achieved.

for flight disturbances (e.g., thrust and center of gravity).

winds) and To provide

equipped with a thrust vector control have been used to redirect the motor

some

guidance

In addition,

or steering

steering

to ensure

is needed

that

to compensate

for vehicle imperfections (e.g., misalignment this steering, solid propellant rocket vehicles

system. thrust

Both mechanical and provide the

and aerodynamic required steering

of are

techniques forces. This

monograph is limited to treatment of thrust vector control systems that superimpose a side force on the motor thrust, steering being achieved by the side force causing a moment about the vehicle center of gravity. A brief review of thrust vector control systems is presented, and two systems, flexible joint and liquid injection, are treated were selected because they are in use on a number of operational likely to be used in future depends upon the particular reliability, development system different from within the restrictions presented

to allow

Treatment

of the

flexible

joint

and

These two systems and they are most

vehicles. The choice between these two systems performance requirements, system weights, cost,

risk, and envelope constraints. However, it i_ possible that a control the selected systems could result in an optimum vehicle performance imposed for particular types of missions. Sufficient references are

investigation flexible-joint its

aerospace vehicle

in detail. vehicles

in detail thrust

insulation

of control vector

against

hot

systems

control motor

other

system gases;

no

than

the

is limited

two

to the

evaluation

the injectant distribution The

design

and within

erosion at the the nozzle.

technology

for

the

injection

two

selected

port

injectant, of the and

systems

design

is presented

movable nozzle, the actuation system, or the means for attachment of the the movable nozzle and the fixed structure. Treatment of the liquid-injection control system is limited to discussion of the pressurization system; no evaluation is presented

selected. of the of the

flexible joint to thrust vector

valves, piping, storage tanks, and nozzle except for (1) the effect of

(2)

the

effect

has

progressed

of injection

to the

point

on

pressure

where

the

basic problems have been overcome and efficient and reliable systems can be designed for any required use. Design problems with flexible joints have been associated with difficulty in establishing the envelope for the movable nozzle; definition of the actuator power

requirements to vector the movable nozzle; definition of allowable properties for the elastomerand the reinforcement; adhesivebonding of the elastomerto the reinforcements; test methodsthat adequatelysimulate the motor operating conditions; and quality control inspection of the molded joint. Design problems in liquid injection systemshave been associatedwith definition of the maximum steering-forceduty cycle; determination of the optimum location and geometry of the injector Valves;andincompatibility of the injectant with many of the materials used for the nozzle walls, seals,and injectant pressurization system. Emphasis in the monograph is placed on those areaswhere specific technical approacheshavesolveddesignanddevelopmentproblems. The material herein is organized around the major tasks in thrust vector control: configuration as related to motor requirements;designparameterscontrolling the response of the mechanism; material selection; system design; structural and thermal analysis; manufacturing; testing, both nondestructiveanddestructive;and inspection.Thesetasksare consideredin the order and manner in which the designermust handle them. Within these task areas, the critical aspects of the performance, structural, thermal, and physical boundary requirementsthat the thrust vector control systemmust satisfy arepresented.

2. STATE OF THE ART

The

vehicle

flight-control

system

must

perform

two

functions:

fly

the

vehicle

along

a

commanded trajectory, and maintain vehicle flight stability in the atmosphere. Vehicles without aerodynamic stabilizing fins normally are unstable, and those with fins may be only marginally stable. Disturbances that effect vehicle attitude and stability include atmospheric winds; motor thrust misalignments due to fabrication tolerances and thrust-vectorcontrol-system offsets such of gravity; and unbalanced disturbances requirements,

be

corrected structural

as those forces with loads,

that occur with flexible joints; during launch and staging. It proper and

timing and aerodynamic

requirements are a function of interrrelated and the vehicle aerodynamic and structural requirements and the design of the control the development of a space vehicle system.

amplitude heating

shifts of vehicle center is desirable that these

so are

that control minimized.

energy Control

effects of disturbances, the trajectory required, dynamics. The determination of flight-control system are two of the most complex problems in

The control system causes a side force to be applied to the vehicle at some distance from the vehicle center of gravity, resulting in a control moment and a change in the vehicle attiude. A number

of force-producing

mechanisms

have

been

employed

or considered

as means

provide attitude and trajectory control of aerospace vehicles. The available considered in this monograph are divided into two main groups: movable-nozzle and fixed-nozzle systems. A classification of the different force-producing associated used, and

with movable and fixed nozzles is shown still others have been evaluated to determine

used include aerodynamic movable 15), and

jet reaction fins (refs.

pintles electric

(refs. 1 to 6), movable external rocket 10 and 1 1). Preliminary evaluations

(refs. 1, 12, 13, and 14), movable arc discharge (ref. 16).

The correct definition and design of the requiring tradeoff analyses between control system as they relate to vehicle performance. vector

control

response, and the systems;

system

are

the

control

plug

(ref.

systems systems, systems have have

motors (refs. 7 to 9), have been conducted 2),

electro

gas dynamic

been been and on (ref.

flight-control system is a complex problem requirements and the penalties of the control Factors affecting the selection of a thrust

moment

required,

the

characteristics

of

vehicle

the stability requirements during flight, reliability requirements, cost restrictions, behavior of the candidate systems. Movable-nozzle systems are linear response i.e., the turning moment is almost directly proportional to the amount of nozzle

vectoring, although directly proportional. rate

in figure 1. Other sytems feasibility. Systems that

to

of injectant

the power required to cause that amount of nozzle vectoring may not be Fixed-nozzle systems generally are nonlinear systems; i.e., twice the

flow

in a liquid

injection

system

does

not

cause

twice

the turning

moment.

TVC

Fixed

J

' Liquid

i

Mechanical

Special systems

deflectors

__J

I

Gas injection

--Jet

I Movable

I

injection l

injection

I

I nozzle i

I Secondary

systems

nozzle

!

I

Low subsonic

High subsonic

_A

I Supersonic

--_Flexible

vane

_____J

-_mbal

joint i

--Flexible --Rotatable

Movable

-Jetevator

L--Hinged

joint --Fluid

bearing/

rolling _Inert liquid

i

I

Warm

gas

--Jet

Pintle --Gimbal

L--Movable

tab

--Fluid

bearing/

plug rolling _Reactive liquid

.-Hot

"Jet

seal

probe --Hinged

--Gimbal

gas _Segmented nozzle

--Ball

&

socket

--Hinged

Figure

1. - Classification

of

thrust

vector

control

systems.

seal

Thrust in the

vector control mechanisms past have been outmoded

have been undergoinging continual by increased severity of operational

development of lighter, more reliable status of the systems listed in figure features of major systems are shown

systems. The general characteristics and technology 1 are presented in tables I through IV; basic design in figures 2 through 11. The systems summarized in

tables I to IV can be divided into three categories: (1) systems systems that have been tested in static firings, and (3) experimental been abandoned or require significant development. Movable rotatable

nozzles.The movable-nozzle systems nozzle and flexible joint) or have been

splitline,

gimbal/integral

change. Concepts used requirements and by

low-subsonic

splitline,

that are systems

(table I) either static fired (e.g.,

supersonic

splitline,

would cause of the vehicle

(2) have

are operational (e.g., gimbal/swivel subsonic and

ball and

of the systems have demonstrated problems or limitations. All movable require that the actuation hardware for the staging maneuvers be carried remainder of the flight. The rotatable nozzle is limited to multinozzle movement of only one nozzle vehicle; effective maneuvering

operational, that either

socket).

All

nozzle systems throughout the motors because

pitch, yaw, and roll forces to be applied to the requires movement of at least two nozzles. The

supersonic splitline and ball-and-socket type are not developed systems, and it is unlikely that further development will be conducted since the other movable nozzle systems have demonstrated all the advantages of these nozzles but with fewer operational and design problems. The

fluid

fluid-filled deflection

bearing/rolling

seal

bearing configured of the rocket motor

deflected as both

(designated

as

TECHROLL

®)

is

a

constant-volume,

with a pair of rolling convolutes that permit omniaxis nozzle. The bearing is shown in figure 8 in the neutral and

positions. The fluid-filled bearing is pressurized by nozzle ejection loads the movable nozzle bearing and nozzle seal. The seal is fabricated

fabric-reinforced

elastomeric

composite

manufacturing processes or tight tolerances. that the actuation torques are lower than

material The those

that

does

not

and serves from a

require

complex

most significant advantage of this bearing is of any other thrust vector control system.

The most significant disadvantages of the bearing are that it has a low rotational stiffness about the nozzle axis in the unpressurized condition, the pivot-point location is limited, and the low lateral stiffness results in larger offset torques than those occurring with a flexible joint.

The

rotational

stiffness

is important

for upper

stages

only

when

vibrational

problems

could occur during lower-stage motor operation. To overcome the limits on pivot-point location, it has been proposed that the rolling convolutes be oriented on a cone; however, this design will increase the actuation torque. The larger offset torque must be allowed for when defining nozzle vectoring angle has been bench tested and static fired joint (ref. 35), thus allowing a direct ®Trademark

of United

* Parenthetical conversion monograph.

units

factors

Technologies

here

and elsewhere

appears

in Appendix

(formerly in the A.

For

requirements. A 24-in. (60.96 cm)*-diameter bearing in a large rocket motor that normally uses a flexible performance comparison of the two systems. The

United

Aircraft

monograph simplicity

Corporation).

are in the International and

brevity,

SI units

System are

not

of Units presented

(SI units). in the

A table

tables

of

in the

TABLE I. - Advantages, Disndvantal|es, and Current Status of Movable Nozzle System

System

Advantages

Flexible joint (refs. 17-30)

State of the art Flexible duty cycle

(fig. 7)

No splitlines Large deflection capability Flexible pivot point location Negligible thrust loss Minimum seal problem Can be used for deeply submerged nozzle Fast response capability Lightweight

Status of Technology

Disadvantages

Operational system for Poseidon C3 first and second stage.

Joint requires thermal protection Joint requires vrotection

of

elastomer during storage Only small tension loads can be applied to joint Joint pivot point is floating, dependent on motor pressure and vector angle Nozzle aligned only at one design pressure and misaligned at all other

(refs. 31 and 32) (fig. 6)

System static fired to 15° vector angle at 355 deg/sec and 300 psi. One static firing, 13-in. and 34-in. throat, submerged nozzles. Three static firings, 2.3-in., 2.6-in., and 8 in. throat. angle at 428 deg/sec and 300 psi.

State of the art

Limited to multiport

Flexible duty cycle Low bearing loadings

Large bearing required Movement of a nozzle results

motors

Operational system for Polaris A2 second stage and Polaris A3 first stage.

in pitch, yaw, and roll forces Nozzle rotation angle much larger than jet deflection

Fluid bearing/

State of the art

Bearing requires thermal

rolling seal

Flexible duty cycle

(refs. 33-36)

No splitlines Large deflection capability

protection Low rotational

(fig.8)

Army Re-entry Measurements Program Phase B; throat diameter approximately 2.8 in., + 8 ° deflection.

System bench tested to 15° vector

pressures

Rotatable nozzle

Twelve successful flight tests on

Negligible thrust loss Minimum seal problem Can be used for deeply submerged or supersonic splitline nozzles Fast response capability Lightweight Minimum envelope required

angle

stiffness about

nozzle axis in unpressurized condition Bearing pivot point is floating, dependent on motor pressure and vector angle

Flightweight systems for Trident 1 (C4) first-, second-, and third-stage motors demonstrated in static firings. Static firings, 4-in. and 10-in. throat, submerged nozzles. Two static firings, 2.44n. and 8.5-in. throat.

Nozzle aligned only at one design pressure and misaligned at all other pressures

Low spring torque (continUed)

/

TABLE I. - Advantages, Dissdvantalles , sad Currant Status of Menmble Noz_

System

Gimbal/swivel subsonic splitline (refs. 37 and 38) (fig. 2)

Advantages

Disadvantages

State of the art Flexible duty cycle Negligible thrust loss Large deflection capability Low-to-medium blowout load Low entry erosion

Excessive envelope required for submerged nozzle High erosion and heat flux in splitline Limited operation time Inflexible pivot-point locations

Systems (oaududed)

Status of Tedmology

Operational system for Minuteman i and 1I first and third stages and Minuteman 111 tint stage. One fullscale firing, 38-in. throat, single external-gimbal nozzle. Two subsonic firings, 15-in. throat, single external-glmbal nozzle. One firing, 4.71 -in. throat, single externalglmbal nozzle.

Gimbal/integral low subsonic splitline (refs. 37-40)

(t_g.3)

State of the art

High blowout

Minimum splitline erosion and heat flux

High actuation torque Large volume required within chamber

Minimum seal problem Continuity of entry, throat, and exit cone Flexible duty cycle Negligible thrust loss Large deflection capability Long burn time durability

load

Medium entry erosion Inflexible pivot-point location Potentially large vectoring envelopes

One firing, 24-in. throat, single submerged nozzle. Two firings, i 5-in. throat, nozzle.

single submerged

One firing, 9.2-in. throat, single submerged nozzle. One firing, 3.9-in. throat, single submerged nozzle. Two f'uings, 1.75-in. throat, single submerged nozzle" +-14 °, 235 sec operation, 163 sec actual firing, 20 pulses, 72 sec coast time.

Supersonic splitline (refs. 41-44) (fig. 4)

Attractive for submerged nozzle

Sealing and erosion problems at splitline

Low entry erosion Lightweight potential Fast response capability Low blowout load

High actuation torque Limited to small vector angles

size: one successful, one failure, single nozzle one-plane motion. Several firings, 4.9-in. throat

High coulomb torque Unpredictable friction torque

One firing, 9.6-in. throat, single submerged nozzle.

Sealing problem Antirotation device required High axial thrust loss

Development

Small deflection Ball and socket (ref. 45)

(fig.5)

envelope

Potentially lightweight Small envelope requirement Large deflection capability Flexible pivot-point location Deflection

Two firings of Minuteman motor, first-stage

of the seal region

is minimized and seal gap is maintained by uniformly distributed load

Notes: Throat dimension in column 4 is throat diamct_. Factors for converting U_. customary units to SI ualts are presented h_ Append_ A.

flexible joint.

discontinued

in favor of

TABLE I1. - Advantages, Disadvantages, and Current Status of Seeondmy In_

Liquid injection (refs. 46-51) (fig. 9)

Disadvantages

Advantages

System

Systems

Status ofTechnology

State of the art

Limited thrust deflection

Operational system for Polaris A3 second

Liquid injection thrust adds to motor thrust

System weight is high Careful attention must be given

little

to selection of liquid and bladder

stage;Minuteman III second and third stages; 120-in. motor for Titan IIIC and IIID; Sprint first- and second-stage motors; Hibex motor; and Lance motor.

prelaunch

checkout

required Fast response capability

material for long-term storage A long hold period after the system is energized requires replenishment of the liquid and pressurization devices Lack of flexibility for accommodation

Development static firings on 120-in. Titan IIIM motor, 156-in. motor, and 260-in. motor.

of changes in control

requirements Must be designed for worst-onworst requirements

oo

Gaseous injection (refs. 52-62)

(fig. lO)

Little prelaunch

check out

required Fast response capability Lighter in weight than liquid injection

systems

Should be linfited to applications

Demonstration

static firing on 156-in. motor.

with required thrust deflection

Demonstration Demonstration

static firing on 1204n. motor. static firings of Minuteman

angles less than 7° Cannot be used where precise velocity control is required Hot-gas valve is subjected to severe thermal environment Warm-gas valve requires large and heavy gas generators Additional propellant necessary to recover thrust losses

Note: Dimensiongiven in column 4 is motor diameter.

motor, first-stage size. Problems concerning durability

of materials

for valves and pintles need to be solved.



TABLE !II. - Advantages, Disadvantages, and Current Status ofMechanical Deflector Systems

System Jetvane (refs. 10,63, and 64)

Advantages Actuation torques are low Small installation envelope around nozzle Power requirements are low, and thus actuator weights are low Fast response capability

Jetevator

Side force is linear with

(refs. 65-69)

jetevator deflection angle

Disadvantages

Status of Technology

High thrust losses Restricted to motors with lowtemperature propellant short burn time

or

Operational system for Sergeant, Talos, and Pershing and for Algo !I and 111 motors. No current development.

Large vane rotation angle required for small jet thrust deflection Jetevator envelopes nozzle exit, restricting maximum available nozzle exit diameter

Operational system for Polaris AI first and second stages and Polaris A2 first stage.

Restricted to motors with low-

Operational system for BOMARC and SUBROC.

temperature propellant short burn time

or

No current development.

Heat shields required to protect afterdome, nozzle exterior, and actuation system significantly increase total system envelope

',D

Large thrust loss (half of generated side force) Torque varies with time System is relatively heavy Limited to multiport systems for omniaxis vectoring. Jet tab

Side force is directly

Restricted to motors with low-

(refs. 70-74) (fig, 11)

proportional to ratio of tab area to nozzle area

temperature propellant burn time.

or short

Caused significant local erosion in the nozzle

Limited to development static firings. Test results indicate significant design and material problems. No current development.

Large thrust loss (equal to generated side force) Jet tabs at the exit plane increase envelope requirements Segmented

nozzle

(refs. 12 and 58)

Major portion of nozzle is fixed to motor Thrust losses at small deflection negligible.

angles are

(Testing to date insufficient to determine disadvantages of system)

Limited to experimental static firings. No current development.

Table IV. - Advantages, Disadvantages, and Current Status of Special Systems

i

System Movable pintle (refs. 1 and 12-14)

Advantages Can be used as a throttling device

Side forceis nonlinear

Omniaxial movement is

Plug subjected to severe thermal environment

C_

Movable plug (ref. 2)

Status of Technology

Disadvantages

possible

with

pintle cant angle Small pintle cant angles produce negative side forces Pintle subjected to severe thermal environment

Analytical and experimental development only. No current development.

Limited to cold-flow air tests. No current development.

Fixed

structure Subsonic

splitline

\

Figure

Low

Fixed

_

structure

Figure

2. - Gimbal/swivel

subsonic

subsonic-splitline

Movable

nozzle

Movable

nozzle

nozzle.

splitline

_ Gimbal 3. - Gimbal/integral

Iow-subsonic-splitline

nozzle.

I Fixed

structure Supersonic

splitline Movable

Gimbal

Figure

4. - Supersonic-splitline

]1

nozzle.

nozzle

ovab le nozzle

Ba 1 i/socket

Antirotation

Figure

5. - Ball-and-socket

Rolling

bellows

nozzle.

bearing Bolted

joint

table nozzle

Seal

Figure

6. - Rotatable

12

canted

nozzle.

Bellows

insulating

boot

_eomet_ic

£orward

pivot

poi

_ctuator

Flexible joint Radiation

/

shield

X

/

I

] Elas

Reinforcement

boot

I

ttOmer

_, ,,

_

_

insulating

bracket

\

nozzle

Wrap-around

_

]

Fixed

_y_

_"

Aft

/

geometric

_pivot

point

I

I (a)

Flexible

joints

with

insulating

boot

Reinforcement

E la s tome

/

r

Ablative

protection

Fixed

Movable

'_Aft

attach

r±ng_

\_

attach

structure

nozzle

ring

i Aft

geometric

pivot

J (b)

Flexible

joint

with

sacrificial

Figure 7. - Flexible-joint

13

ablative

nozzle.

t

protector.

point

_---

1

'_

_l_u_: one

Falbric_reinforced

neoprene

bladder

Pivot

-

point (a)

Neutral

position

Extended

side

.Vector

angle

,ressed ide_

(b)

Figure

Vectored

position

8. - Fluid-bearing/rolling-seal

14

nozzle.

Act

us for

bracket

Actuator

Exit

_lild

cone

tank_ valve (a)

External

(b)

Submerged

Figure

9. - Liquid

nozzle

nozzle

injection

Gas

TVC

system.

injectant

I

Hot-gas

valve

Motor

Figure

10. - Hot-gas

TVC

]5

system,

leg mounted.

_

._ XIE cone

xit

Exit

(b)

Submerged

Figure

11.

cone

cone

nozzle

- Jet

tab

16

TVC

systems.

comparison showed that the actuation percent of the actuation torque for the (60.96 cm) diameter have been tested vectoring 35

rates

and

36).

vector

up to 40 An

angles

demonstrated

The

(20.32

and

2) of for for

or

flexible

pressures

rates

bearing up

up has

to 1000 been

to 140 deg/sec

tested

and

for

an

operational

flight

motor

MN/m 2) (refs.

in static

motor

and

firings

pressures

up to

up to 2700

therefore

will

not

be

in this monograph.

joint

has

demonstrated

the

capabilities

of the

gimbal

development problems, has been demonstrated in a number operational in the first- and second-stage motors for Poseidon treated in detail in this monograph (secs. 2.1 and 3.1).

Liquid (table

psig (6.89

for firing times of 20 seconds (ref. 35). This bearing has also been tested + 15 °, vectoring rate of 762 deg/sec, and motor pressure of 2100 psia a firing time of 5.5 seconds (ref. 35). The fluid bearing/rolling seal has use in a large high-performance motor, but as yet has not been

accepted

further

motor

cm)-diameter

of + 12 ° at vectoring

psia (18.6 MN/m at vector angles (14.5 MN/m 2) been selected evaluated

8-in.

deg/sec,

torque for the fluid bearing/rolling seal was 30 flexible joint. Fluid bearing/rolling seals up to 24-in. in static firings up to vector angles of -+ 6.5 °, at

injection.II) has been

A large amount accumulated. The

of experience liquid-injection

splitline

but

with

fewer

of flight motors, and C3; therefore, this joint

on secondary-injection system is a state-of-the-art

is is

TVC systems system that

is operational on several vehicles. This system has the advantage over the movable-nozzle system in that most of the excess liquid can be dumped after staging and recovery of flight attitude, the vehicle thereby having less inert weight during the remainder of the flight than the vehicle that must continue to carry nozzle actuation hardware. Hot-gas injection systems are promising, but valve and piping problems due to the severe thermal be solved. Warm-gas injection systems reduce the thermal environment large

and

heavy

this monograph

Mechanical

gas generators. (secs,

systems.-

The

2.2 and

The

liquid-injection

system

therefore

is treated

in detail

listed

table

either

mechanical

are no longer being considered weights and material problems now

plug under

(table

IV) have

not

in

3.2).

deflector

systems

on

operational (e.g., jet vane and jetevator) but have now been replaced were limited to development static firings (e.g., jet tab and segmented

and

environment need to problem but require

in the industry. These techniques due to exposure to hot exhaust advanced

beyond

development.

17

limited

experimental

III

were

by other systems, or nozzle) and in general

generally suffer from high gases. The movable pintle evaluation

and

are not

2.1

The

FLEXIBLE

flexible

movable

joint

nozzle

JOINT

is a nonrigid that

direction*. The deflection moment about the vehicle Two

kinds

of flexible

position in figure descriptive terms definitions appears

2.1.1

pressure-tight

allows

the

nozzle

joints

are

shown

of the

a movable any

in figure

by

the

rocket

as much

as

motor 15 ° in

and

a

a given

the motor thrust vector and generates altering the course of the vehicle. 7. The

flexible

joint

13. These complete

is shown

a

in a neutral

figures also show list of symbols

the and

Configuration rings of an elastomeric These rings are usually

flexible

nozzle. direction.

elastomeric part of the

Since When

components total vector

material spherical

alternating with rings of sections with a common

to as the geometric pivot point. A joint wherein the rings were sections has been designed and successfully tested (ref. 22). This of requiring a single set of tooling for all the rings rather than

tooling for each ring as is necessary the joint was limited to a cylindrical

in

between

deflected

12 and in a vectored position in figure used throughout this monograph. A in Appendix B.

center of radius referred identically shaped conical design had the advantage

end

connection be

of the nozzle deflects center of gravity, thereby

The flexible joint consists of metallic or composite material.

One

to

joint the the

with spherical envelope.

is connected joint

rings.

to a fixed

is symmetrical

nozzle

are strained angle, and

is acted

Since

each

ring had

and

the other

structure,

about upon

its centerline, by

an

the

same

is connected

the nozzle

external

shape,

actuator

to

can vector force,

the

in shear, each reinforcement ring rotates a proportional the nozzle rotates about the effective pivot point (fig.

13). Usually the effective pivot point does not coincide with because of different amounts of distortion in each reinforcement.

the

geometric Omniaxis

pivot point movement of

the nozzle is obtained by using two actuators 90 ° apart. In addition to providing a means for thrust vectoring, the joint also acts as a pressure seal. Flexible joints are designed so that the axial compressive pressure imposed on the elastomer is higher than the chamber pressure. An important property of the elastomer in the operation compressive modulus is approximately 15 000 times the shear

* This

amount

of

motion

has

been

demonstrated,

but

an upper

limit

to deflection

of a joint is that the bulk modulus. This relation means

angle

has

not

been

established.

18 '\

Ro + Pivot

radius

Geometric

pivot

point,common center for Joint

joint angle

_1

Outer

joint

as tomer Reinforc

Figure

12. - Flexible

joint

]9

all

angle "oint

Inner

Ri

Rp =

in neutral

position.

ement

angle

radii

Deflected

joint

Original

joint

Geometric

Vector

angle

@

envelope

pivot

point

point Effective

I,

/----

Joint

0

U

Deflected

joint

0

0

__.._ .-

Rotation \

jl

Figure

about

13. - Flexible

joint

20

effective

in vectored

occurs pivot

position.

point

pivot

that a joint but permits

can transmit high axial compressive high shear deflections at low applied

The reinforcements to motor pressure

cylinder

The

nozzle

with

section,

the

movable

flexible joint. fixed structure

DESIGN

Flexible-joint reinforcement materials

when

an actuator a

actuation is discussed

design

protection.

These

motor

requirements

design

previous

;_,applied ai>plied geometry apart each

of

structure,

four the

main

subsystems:

actuation

system,

pressure,

(ref.

is dependent

incremental analysis increment

when

the

joint to the in reference

joint

and

actuator

not

in the plane cross section

be

must

be selected

the number layers, and

of the

combined

to

and

angle,

and

envelope

constraints

must be determined in studies joint design requirements and

are specified. to define the stage

the and

77).

on many

geometric

variables,

and

no general

solution

for joint

is based on empirical relationships (refs. 17, 23, 78, and by finite-element techniques (refs. 80, 81, and 82), and to the analytical results. Analysis of a flexible joint is of and joint

procedure is conducted, and

elements

vector

material properties, large deflections and strains, nonsymmetric geometries during vectoring. However, test results and calculated results has been obtained by (ref. 80). The using material

a geometry

determined

load is axisymmetric, the deflected load is asymmetric (e.g., an actuation will

joint

the and the

performance, and reliability at minimum weight and Joint design is affected also by the attachment to the nozzle. In some programs, the basic joint design

these design requirements relationship between the

complicated by nonlinearity nonsymmetric loading systems, reasonable correlation between

the

consists fixed

system on the flexible in this monograph.

design exists. Preliminary design 79). A selected design is analyzed the design is modified according

use of an finite-element

and axial loads due sideways as would

consists of the determination of the joint configuration, the material for the reinforcement rings and elastomeric

including programs, tradeoff

joint

deflections,

OPTIMIZATION

design rings,

requirements

The

axial

was applied.

joint to the

provide the required spring stiffness, within cost and envelope limitations. fixed structure and the movable

vehicle

load

flexible

attachment

for environmental

In other optimum

resulting

The movable-nozzle section and the attachment of the flexible are treated in reference 75, and actuation systems are treated

76. The effect of the characteristics interact

2.1.1.1

low

provide rigidity to the joint against motor pressure and constrain the joint to vector instead of deflecting

an all-elastomer

movable-nozzle

loads with torques.

axisymmetric.

of actuation have is axisymmetric

from

the

previous

increment.

geometry will be axisymmetric. load applied by one actuator),

The

deflected

been (refs.

analyzed 22 and

21

load is applied incrementally, properties associated with the

geometries

at two

cross

and a stress at When

the

the •

When the deflected

sections

180 °

by finite-element methods that assume 78). Methods of mathematical analyses

other

than

the

finite

material

anisotropy

2.1.1.2

ENVELOPE

The

joint

element (refs.

envelope

have

been

employed

to consider

(fig.

angle/32 /32-55 The

12) nor

difference

minimum

value

deformations

and

LIMITATIONS is defined

by the

less than

pivot

0 °. It has

up to 70 ° are feasible; °- may

joint

83 and 84).

radius

Rp,

the inner

/32, and the cone angle _b (fig. 12). The pivot radius is throat diameter, but the inner and outer joint angles designer. All joints that have been successfully tested to 40 ° to 45 °, angle t32 ranging from 45 ° to 55 °, and angle angle/3

finite

not be the

limit.

between

the

possible

without

these

inner

been

and

suggest

outer

exceeding

joint

the

outer

joint

angles

131 and

determined primarily by the nozzle and cone angle are selected by the date have had angle/31 ranging from ¢ that was not greater than the joint

demonstrated

results

and

by

that

analysis

the largest

angles

allowable

that

joints

demonstrated

with value

for

at

the

(/32 -/31 ) is maintained

elastomer

stresses,

so that

an

the joint

spring torque is kept to a minimum. It has been shown analytically (ref. 17) that the cone angle significantly affects the joint axial deflection and the elastomer and reinforcement stresses. As the cone angle increases, these values increase, and the effective pivot point moves farther from the geometric pivot point (fig. 13). However, decreasing the cone angle has resulted in nozzles with large section of the nozzle and require the

amount

Cost

also

with

has been

cylindrical

2.1.2

that increase the weight of the movable envelopes in the motor, thereby reducing

of propellant.

conical-shaped

section,

re-entry sections larger clearance

envelope thus

reducing

a factor

in determining

reinforcements

was

(_b =/3 as shown tooling

and

the joint

The must

A large The

on fig. 13), and each

fabrication

joint

flexible was

reinforcement

joint

designed had

the

(ref.

22)

with same

a

cross

costs.

Design Requirements

The requirements affecting the design of a flexible angle, axial deflection, frequency response, motor sealing,

envelope.

manufactured.

cost,

actuation

joint are nozzle actuation torque, vector pressure, environmental effects, pressure

and weight. torque

be estimated

(sec. for

2.1.2.1),

preliminary

is made design

up of many and

subsequently

vector angle (sec. 2.1.2.2) required to produce sufficient dependent on the position of the pivot point (fig. requirements.

Axial

deflection

(sec.

2.1.2.3)

affects

22

contributing

the

torques,

checked

in static

each

of which

firings.

The

maneuvering force on the vehicle 13) and the vehicle performance clearance

envelope

required

between

is

the fixed and movable portions of the nozzle; in addition, the axial deflection controls the axial spring stiffness of the flexible joint between the fixed and movable nozzle sections. The natural frequency and frequency responseof the movablesection(sec.2.1.2.4) depend upon the axial stiffness and the massproperties of the movable section. The frequency responseaffects designof the actuator andguidancecontrol system;sufficient stiffnessmust be designedinto the movablenozzleto avoid dynamic coupling of variousforcing functions. The motor pressure influences the selection of the joint materials and dimensions and affects the joint responseto all of the aforementioneddesignrequirements.The joint needs to be protected against a high-temperature environment on the motor side and the atmospheric environment on the outside (sec. 2.1.2.5). In addition, the joint must be a pressuresealbetweenthe motor andthe atmosphere(sec.2.1.2.6). Flexible joints with elastomericringsformulated from natural rubber havebeen operatedat elastomer temperatures ranging from 65° F (291 K) to 85 ° F (302 K), and have been vectored

in motors

operating

up to 600

not less than 65 ° F (291 acceptable results in bench (ref. 85).

2.1.2.1

ACTUATION

In order accordance

(182

required. The actuation torque total torque is the summation

including torques due to internal the following component torques: •

Joint



Frictional



Offset



Inertial



are

spring

and

external

torque torque

torque torque

Gravitational

identified

900

m) altitude

with

the

elastomer

at

has demonstrated K) to 165 ° F (347 K)

TORQUE

to define the requirements of the control with the motor or vehicle requirements,

actuation torque pivot point. The

Materials

000 feet

K). A joint with neoprene*/polybutadiene tests at temperatures from -40 ° F (233

torque

in Appendix

B.

23

system and to actuate the the designer must know usually is defined of a number of

aerodynamics.

The

total

about the contributing torque

nozzle in the total geometric torques,

is made

up of

• Insulating boot torque • Internal aerodynamictorque o The

External

total

aerodynamic

actuation

torque

torque

varies

from

motor

to motor

and

from

cycle

to cycle

continuous sinusoidal cycling on the been determined to be -+ 20% (refs.

nozzle. The total variability 86 and 87). The variability

including of a new

determined,

be

not_ identical

since

prior

results

may

based

on joints

that

are

during

both items has design must be to

the

new

design. 2.1.2.1.1 The

Joint Spring Torque

flexible-joint

spring

torque

(resistance

of

maximum torque contributing to the actuation factors: total thickness of elastomer, pivot radius, affected '2.1.2.5.2).

by

environmental The resistance

• convenience

of analysis,

geometric

pivot

point

the

joint

necessary

torque

to the line of action

The spring torque is dependent on the combined on the thickness of each ring (ref. 17). The spring of the pivot radius (i.e., Tq _ Rp 3 are a minimum, the joint diameter

mechanical is overcome

is calculated

of the

movement)

torque. It is dependent joint angles, and motor

effects on the elastomer of the joint to movement the

to

as the

usually

on a number of pressure; it is also

characteristics by the actuator; moment

arm

(sec. for

from

the

actuator. thickness of all the elastomer torque is roughly proportional

rings and not to the cube

Therefore, to ensure that the spring torque is minimized by placing the joint as close

).

is the

and envelope to the throat

plane as possible; the pivot radius is then made as small as possible, but not so small as to increase the stresses in the joint above the allowable values. The inner and outer joint angles /31 and/32 (fig. 12) control the joint thickness. is kept to a minimum consistent with the

As noted, elastomer

the difference between allowable stresses. The

these joint

angles spring

torque reduces attributed to

as the motor pressure increases the effect of compression on

(refs. 13, 22, 86, and 87). This phenomenon the elastomer shear modulus properties,

configuration

of

in shape

the

joint,

and

the

change

of

the

joint

(refs.

83

and

is the

84).

If

sufficient pressure is applied, the spring torque can become zero. Little data are available on the variation in spring torque. Tests conducted on joints for two different motors that used a natural-rubber formulation show a variation of + 20% at zero pressure. This torque variation in absolute units remained approximately constant and independent of motor pressure modulus For

rapid

(refs. 86 and 87). The variation of the elastomer (sec. 2.1.3.1 ). calculation

number of equations correlation with test

of the have results

Spring

was correlated

torque

for joints

with

with

lot-to-lot

spherical

variation

reinforcement

in the shear

rings,

a

been developed (refs. 17, 21, 23, and 78). Of these, the best for many different joints is the expression (adptd. from ref. 78)

24

_

Tq 0

12Goroari ro 3_

ri 3

(1)

3 [I(fl2)-I(fl,)]

where = joint

Tq

spring

0 = vector Go

torque,

angle,

= elastomer

in. - lbf (m-N)

radians

secant

shear

modulus

at 50 psi (0.345

MN/m 2)

shear

stress (sec. 2.1.7.1), with no externally imposed pressure, at the elastomer temperatures expected in operation, psi (N/m 2) ro

= Rp

+ nte/2,

in. (cm)

q

= Rp

-

in. (cm)

Rp t_ n

_, _

nte/2,

= pivot

radius

= thickness

of individual

= number = inner

of elastomer and

I(f3) = integral

in. (cm)

outer

values

TABLE

V.

elastomer

in. (cm)

rings

joint

angles,

listed

in table

-

layer,

deg V (ref.

78)

Integral Values 103) for/3 = 15 ° to/3 = 60 ° (ref. 78)

fl, deg

10)

/3, deg

15

0.0518

27

16

.0588

28

.1713

40

.3249

52

.4999

17

.0661

29

.1828

41

.3389

53

.5148

18

.0739

30

.1946

42

.3531

54

.5298

43

.3674

55

.5448

/3, deg 39

0.1601

t_) 0.3110

/3, deg 51

I Wig) 0.4849

19

.0820

31

.2067

20

.0906

32

.2189

44

.3818

56

.5599

21

.0995

33

.2315

45

.3963

57

.5749

22

.1088

34

.2442

46

.4109

58

.5899

23

.1184

35

.2572

47

.4256

59

.6048

24

.1283

36

.2704

48

A403

60

.6198

25

.1386

37

.2838

49

.4551

26

.1492

38

.2973

50

.4700

25

From

test

data,

the

following

pressure has been natural-rubber-formulation

empirical

developed elastomers

Tq

relationship

for (adptd.

0.156Gro

0

--

calculating

joints with from ref. 78):

3 ri 3 (/32 -

ro 3

for

steel

the

spring

torque

reinforcements

/31)

at and

(2)

ri 3

where G

= effective

elastomer

pressure, = Go A

shear

modulus

when

subjected

to external

psi (N/m 2 )

+ Ao 2

= constant

(3)

depending

= - 0.2595

upon

reinforcement

material

x 10 -6 for steel Pc sin2/32

O2

(sin2/32

Pc

from

joints

with

equation

cone

Friction bearings friction

torque in and O-rings. theoretically major

cos 2 q_

psi (N/m 2)

deg

angles

(2) have

Friction

three

pressure, angle,

2.1.2.1.2

from

- sin2/31)

= motor

q_ = cone

For

(4)

=

agreed

varying within

from

15 ° to 50 ° , at high

+ 8% with

torques

measured

pressure, in bench

torques

calculated

tests.

Torque a conventional movable nozzle arises from sliding surfaces Since there are no sliding surfaces in a flexible-joint nozzle, does not exist. Elimination of the joint friction eliminates

sources:

26

such as coulomb problems

(1) Friction varies significantly from unit to unit and cannot be predicted with accuracy. (2) Friction is the major sourceof steady-stateerror in the servoactuator system. (3) The changefrom static to sliding friction causesa breakawaypeakin actuation. Although there is no sliding friction in a flexible joint, the joint doesrespondto actuation in a manner similar to that of a spring-masssystemwith both viscousfriction and coulomb friction. The viscousfriction probably is associatedwith the viscoelasticbehavior of soft elastomeric materials. Viscous damping is an important consideration in determining the stability characteristicsof the thrust vector control system. No methods are availableto calculate either coulomb friction or viscous friction. Attempts to calculate the damping coefficient from the decaying actuator force transient occurring at the end of a step vector-angle function applied to a nozzle have been unsuccessfulbecauseno correlation could be obtained with the friction coefficient calculated from actuation data. For sinusoidal actuation of the nozzle, the viscoustorque component doesnot contribute to the maximum actuation torque, sincethe viscousfriction torque is a maximum when the nozzle is at zero position andzero when the nozzle is fully vectored. The coulomb friction and viscous friction are determined experimentally. A nozzle is vectored at different frequencies but constant amplitude, and the actuator force is measured.A typical actuator force responseis shown on figure 14(a); the actuator force at zero vector angle is the total friction. When the variation in total friction force with vectoring rate is plotted as shown in figure 14(b), the two friction components can be determined. Experimental data have shown that for joints fabricated by the samemanufacturer the variation in viscous friction is -+30% and for coulomb friction is -+15%(ref. 88). Joints fabricated by different manufacturers to the same specifications have demonstrated significantly different friction torque results,although the variability wasapproximately the same. Test results have indicated that the viscous friction is dependent on vectoring amplitude in addition to vectoring rate. The coulomb friction has been shown to be dependent on vectoring amplitude and pressure.The phenomenon of friction is little understood, and the elastomerproperties anddimensionsinfluencing friction havenot been identified. 2.1.2.1.3

Offset Torque

Offset torque manufacturing during additive

is the torque tolerances.

resulting from Consequently,

motor firings. The offset torque to that due to nozzle vectoring°

asymmetry in the nozzle offset torque can occur

due to misalignment and in bench tests as well as

during a motor firing is an aerodynamic torque The amount of alignment offset is dependent on

27

t Total

frequency

friction

+ Vector

Total

--

Response

friction

to

slnusoldal

different Highest

(a)

angle

actuation

at

frequencies

frequency

Variation

in

vector

angle

with

sinusoidal

actuation

force

O 4J U v_4

Rate-dependent

component

(viscous

friction)

! 4J O

Rate-independent

Maximum

(b)

Figure

14.

Variation vectoring

- Graphical

vectoring

in total rate

presentation

component

friction

of

the

28

effects

(Coulomb

friction)

rate

with

of

maximum

friction

sinusoldal

in a flexible-joint

nozzle.

axial deflection characteristics be at zero vector angle (sec. diameter has been small determining the actuation torque

could

2.1.2.1.4

of the joint 2.1.2.3). The

contribution

to the

actuation

torque is determined the movable section

by assuming of the nozzle

of the vector

the

actuation

it is ignored in joints the offset

torque.

joint acts with the angles at zero motor

spring

torque

cycles,

and

even

produced The inertial

less

to a fixed structure, and in the determination movable nozzle it is usually assumed that half

movable pressure,

at high

is much

point resulting from accelerations on the vectoring acceleration.

that the mass of the nozzle acts at the center of gravity of and that the movable section vectors about the geometric

pivot point. One end of the joint is connected of section mass and center of gravity of the

with

at which the nozzle must up to 22-in. (55.88 cm)

Torque

The inertial torque is the torque about the pivot on the nozzle by the actuator and is dependent

the mass maximum

pressure for joints

in comparison with the spring torque, and torque. However, it is possible that for larger

be a significant

Inertial

and the motor offset torque

section. For joints the inertial torque

vectoring

than

the

rates

up

variability

to

designed to demonstrate usually is small compared

500

in actuation

deg/sec

for

torque

from

sinusoidal motor

to

motor. 2.1.2.1.5

Gravitational

The gravitational movable nozzle maneuvers,

Torque

torque is the torque produced mass as a result of accelerations

pitch,

yaw,

and

axial

gravity, causing axial and lateral As before in the determination assumed usually

to act with is small

with

2.1.2.1.6

Insulating-Boot

A flexible

joint

7).

Either

separates The

this

often

wrap-around

a wrap-around a 13-in. (33

and boot

section. the

accelerations

booster

is protected boot

against

hot

is wrapped

motor

1255

center

vehicles,

of

nozzle. mass is

the gravitational

directly

gases by use of an insulating

torque

around

the

joint,

or

boot

a dead

air

(fig. space

the boot. adds

significantly

to the

nozzle

boot fabricated of silica-filled butadiene cm)-diameter joint increased the actuation

DC

vehicle

torque.

m-N/deg) to 2100 in.-lbf/deg (237 m-N/deg) changed to a bellows type (fig. 7), the actuation 1600 in.-lbf/deg (180 m-N/deg) (ref. 14). incorporating

at the

at the center of gravity of the movable and center of gravity, half of the joint

For large

spring

occur

by the vehicle

Torque

insulating

the joint

lateral

accelerations of net mass

the movable

compared

and

about the geometric pivot point imposed by the vehicle. As the

silicone

rubber

resulted

29

vectoring

torque.

For

acrylonitrile rubber torque from 1000

example,

use of

(GTR V-45) on in.-lbf/deg (113

(ref. 13). When the design of the boot was torque increased from 1000 in.-lbf/deg to A wrap-around boot design (fig. 7(a)) in a 20%

increase

in actuation

torque

for a

joint 22 in. (55.88 cm) in diameter. This was

found

to be

i_ct_ase 'was ratio of joint

dependent

on

increase was not uniform from joint to joint the boot was bonded to the reinforcements:

whether

greater when the boot was diameter to insulating boot

bonded thickness

to the reinforcements. In general, as the increases, the proportionate increase in

actuation attributable percent.

torque due to the boot will be less. to the insulating boot for a joint 112

2.1.2.1.7

Internal

.... _ '"_Th_ :internal

Aerodynamic

aerodynamic

For example, the increase in torque in. (2.84 m) in diameter was 11 to 15

Torque

torque

acting

on a submerged

nozzle

is the

result

of unsymmetric

flow between the around the vectored

propellant grain and the movable nozzle. Pressure nozzle cause side forces and a resultant torque.

variations

If the

pivot

is forward

torque

torque

and

point hence

and the

of the

is an increment

nozzle

to the

throat,

actuation

the

aerodyl_amic

torque

and

needs

that

occur

is a restoring

to be calculated.

If the

pivot point is aft of the nozzle throat, the aerodynamic torque is sustaining and reduces the actuation torque (ref. 23). For an aft pivot point, the aerodynamic torque usually is ignored in calculating the actuation torque, thus ensuring a conservative estimate for actuation torque.

However,

if a system

were

designed

to be vectored

only

at pressures

that

result

in a

low spring torque, the aerodynamic spring torque and produce a negative tolerated in a closed-loop system.

torque with an aft pivot point could actuation torque. A negative actuation

The aerodynamic torque is calculated point produced by the pressure forces knowledge of the wall static pressure

by summing the moments about the geometric pivot acting on the nozzle wall. This procedure requires a and the pressure differentials existing in the nozzle.

Two procedures are available airflow simulation tests (ref.

for developing the internal 89), and a two-dimensional

overcome the torque can be

wall pressure in a vectored method-of-characteristics

nozzle: solution

(ref. 90). When the aerodynamic torque is calculated from the results of a_rflow simulation tests, the calculated value generally is within + 20% of the measured value. When the aerodynamic torque is calculated from the results of a two-dimensional method-of-characteristics analysis, the result generally is within + 50% of measured value. As the grain burns and the clearances between the nozzle and the distribution becomes more symmetrical, so that the aerodynamic significance near the end of propellant burn. 2.1.2.1.8

External

Aerodynamic

In

specific

cases,

pressure of little

Torque

During flight, the external air stream impinges on the component, especially in the high dynamic pressure required.

grain increase, the torque becomes

this

effect

perhaps

30

nozzle region could

exit cone and creates a torque when large vector angles are be

utilized

to

increase

the

maneuverability of the vehicle in this flight region or to provide vehicle control after motor burnout. The external aerodynamictorque could be calculated from the pressureacting on the nozzle exterior surface in the same manner as the internal aerodynamic torque is calculated(sec.2.1.2.1.2). However, in most boosterapplications, the exit coneis shrouded by a motor caseskirt that preventssignificant air impingementthat would causean external aerodynamictorque. 2.1.2.2 The

NOZZLE

amount

the

nozzle

The

pivot

VECTOR

of nozzle

vector

is vectored, point

Vectored

can

nozzle,

Vectored

nozzle,

ANGLE

the be

pivot

PIVOT

side or aft

force of the

by the vehicle acts

aft

control

approximately

nozzle

throat

(fig.

requirements.

through

the pivot

15).The

position

/

pivot

Envelope

for

forward

pivot

point

point

for

forward

pivot

point

Envelope

1

,._

_SS

_ aft point _

| _J

Nozzle

in

neutral

position Forward

pivot

point Aft

Figure

point. of the

pivot

for

Envelope

When

point

/ Envelope

POINT

is determined

resultant

forward

forward

aft

angle

AND

15. - Effect

of pivot-point

pivot

position

31

point

on required

envelope.

pivot

for

geometric

pivot

point

is selected

from

a tradeoff

on the exterior clearance envelope between the and stroke to fulfill vehicle guidance requirements, movable

nozzle

presented

in table

A summary

of the

comparative

study

that

considers

the

effect

of position

fixed and movable parts, the actuator force and the spatial envelope available for the effects

of a forward

or aft pivot

point

is

VI.

TABLE VI. - Comparative Effects of Forward and Aft Geometric Pivot Point Comlmmtive effect Item

Reduced

Increased

Clearance envelope for exit cone

Increased

Reduced

Actuator stroke to produce a particular vector angle

Increased

Reduced

Actuator force to produce a particular vector angle

Reduced

Increased

Vector angle to produce a particular vehicle movement

Increased

Reduced

pivot point less envelope

will reduce the moment arm to the vehicle center angle to generate the necessary turning moment.

will reduce the required vectoring angle. A forward for movement of the nozzle nose cap region but more

exit cone (fig. 15). The moment arm from the forward pivot point, and therefore less actuator cone movement is increased, the actuator stroke Because

of the

recluced

nose-cap

movement,

(fig. 15). Regardless of whether tested to date has been between

pivot

points

generally

is greater with a because the exit

are

used

for

the motor chamber. Aft pivot points generally because the envelope for exit cone movement movement reduces the envelope available for

a forward or aft pivot 45 ° and 50 °.

32

of gravity Similarly,

pivot point will envelope for the

pivot point to the actuator force is required; however, is increased. forward

nozzles having little or no submergence into are used for nozzles having deep submergence, is critical. However, the increased nose-cap propellant t3 on joints

Aft pivot

Clearance envelope in nose cone region

As shown, a forward pivot point and thus require a large vectoring an aft require

Forward pivot

is selected,

the joint

angle

The position of the effective pivot point is dependent upon the applied loads and joint configuration. The actuator force, in addition to vectoring the joint, causes a movement of the joint in the radial and axial direction, so that the effective pivot point is offset from the geometric differently,

pivot point (fig. 13). Vectoring of the joint causes strongly influencing the position of the effective

each reinforcement to deflect pivot point. At zero motor

pressure, only the actuator force causes pivot point movement. At motor pressure, compressive load is applied to the joint and causes additional pivot point movement. 16 shows the measured pivot point movement for three different joints varying inches (53.3 cm) and at maximum by decreasing reinforcement reinforcement

diameter expected

to 112 inches (2.84 operating pressure.

an axial Figure from 21

m) diameter, vectored at zero motor pressure The pivot point movement can be decreased

the cone angle. Analytical studies (ref. 17) have indicated that the stresses decrease as the cone angle decreases (sec. 2.1.5.3), because the deflection decreases. Reduced reinforcement deflection results in reduced

pivot point movement. As shown in figure 16, pressure lateral movement of the pivot point due to vectoring. A knowledge

of the

effective-pivot-point

location

acting

on the joint

is important

also reduces

in establishing

the

the

clearance

envelope between the fixed and movable nozzle components. In one flexible-joint program, the effective pivot point was assumed to have moved an amount equal to the axial deflection, and a clearance envelope was set up accordingly. It was subsequently determined that the effective pivot point had moved approximately 1.5 in. (3.81 cm) while joint axial deflection was 0.4 in. (1.02 cm). The allowed clearance envelope was too small and had to be increased

by removing

predicts the lateral pivot-point position

2.1.2.3

AXIAL

Although

the

joint.

No

method

has

been

An approximate in the following

developed method section.

that

accurately

to determine

flexible

joint

stiff

in compression

in comparison

amount of axial compression occurs when the axial compression to determine nozzle

spring

acts to increases

is relatively

stiffness,

reduce some the vectoring

and

the

nozzle

clearances clearance

misalignment

between around

with

its vectoring

the motor is pressurized. envelope requirements, requirements.

axial the

properties envelope,

compression cone angle. in and

is dependent The axial

on the elastomer stiffness, the reinforcement compression involves an interaction among

compression, deformation the ratio of the dimensions

of the of the

33

The

It the axial

the fixed and movable nozzle the exit cone, and influences the

position of the pivot point. The spring stiffness is required in the design of the control system. The fixed-length actuator causes vectoring of the nozzle by motor and the nozzle is misaligned at zero pressure so that it is aligned at some required The and

the

DEFLECTION

compressive

compression components,

of the

movement of the pivot point. due to axial load is presented

stiffness, a measurable is necessary to know axial

part

elastomer, elastomer

guidance pressure, pressure. stiffness, elastomer

reinforcement stiffness, rings to the reinforcement

joint rings.

Force Joint

description

system

geometric

st

pivot

eosition

of

with

respect

point

effective to

pivot

(a) Mean

Joint

diameter

m

112

53

radius angle

m 73 50 °

-

in.

motor

pressure

Geometric

(1.85

000

lbf(2.358

x

105

pivot

point

N)

m) Aft

Vector

angle

point

in.

(2.84 m) Pivot Cone

Zero

pivot

geometric

6

ffi 2 °

in.

(£5.24

cm)

+ .I x (5.76

106 x

--_

in.-Ibf 105 m-N)

_Axial position is reference

Effective pivot point

plane

5-1/2 (b)

At

motor

pressure 3.97

49

000

Ibf

(2.180

1.15

x

x

105

10 6

(5.115

x

+---_

Ibf

10 8

cm)

N) Geometric N)

pivot

I-I/2 point Effective--

4.8 _*_----_/(5.42

x

1061n.-Ibf x 105 m-N) Joint

cm)

1

pivot

point

axial

deflectiou

pressure

in.

_---T(3,8i

Aft----Im_

ffi0.24

st

in.

(6.10

mm)

Geometric Mean

Joint

(53.3 Pivot Cone Vector

diameter

=

21

(a)

ih.

Zero

cm) radius angle angle

motor

1770 ffi 13.90

in.

(35.3

pressure

15f(7873

N)

I

in.

point

___/plvot

ca> $/__/

Aft

cm)

0.5

ffi 50 ° = 5°

1480

Ibf_(6583

+----.. 6327

At

(b)

:(1.27

iolhf

m-N)

t^ft...

Effective

pivot

210 000 ibf (9.341

x

105

N)_

835

N)

Aft_

ibf(3714

32 000 m_...._/(3615

point

2-1/4 _---

Ibfi(4448

om)

_

pressure

motor

I000

in.

N)

_

Aft

(5.71in. cm)

N)

.

0.02

Geometric pivot _Int

in.

(0.5

*mu)

ff tlve pivotS--- t

in.-ibf m-N)

point

Joint

axial

at

ffi0.4 pivot

Effective Zero

motor

1130

Ibf

(a) Mean

Joint

(53.7 Pivot Cone Vector

diameter

-

21.14

angle

_ 13.70 50.5 ° -

in.

(I.02

pressure

In.(34.80

(5026

N)

_

I

3100

ibf(13789

Aft

T

cm) 0.14

N)



in.

(3.6

ram)

,%___t 000 (5197

in.-ibf m-N)

pivot

Geometric

Effective (b)

At

motor 785

Ii0

000

lbf

point

pivot

pressure

Ibf(3491

N)

(5.08

cm)

_ [

point

0.02 2160

lbf

(9608

in.

N)

I

(0.5 (4.893

x

i0

N)_

32

000

in.-ibf

(3615

m-N)

of pivot

point

for

34

three

point

mm)

| Aft-Jm_

at

16. - Movement

pivot

Geometric

Joint

Figure

ca)

point

in.

cm)

radius angle =

deflection

pressure

different

axial

pressure

flexible-joint

deflection -

O.3

in.

(7.6

nozzles.

_n)

Test

results

have

shown

compressive

loads

The

conditions

loading

compression

load

that

(refs.

these

22, 86, and for

due

interactions

in a nonlinear

response

to applied

axial

87).

a flexible

to the

result

joint

motor

consist

pressure

of an external

acting

on

the

radial

movable

The axial compression load due to motor pressure is calculated acting on the movable section. Solutions in the form of

pressure section

and

an axial

of the

by integrating equations to

nozzle.

the pressures predict axial

compression have not been satisfactory. Measured deflections have been as much as four times the calculated deflection. Most success in predicting axial compression has been obtained with computerized finite-element methods of analysis (refs. 78, 81, and 82). Reasonable correlations between calculated and measured axial deflections have been made with

the

use

of a sequential-loading

finite-element

method.

The

geometry

of the

joint

for

each loading increment is changed to the deflected geometry due to previous loading increments. For each loading increment, the elastomer shear modulus is assumed constant at the secant shear modulus at 50 psi (0.345 MN/m 2 ) shear stress (sec. 2. i .7.1), and all other elastomer ratio

properties

are

determined

assuming

isotropy

and incompressibility

(i.e., Poisson's

= 0.5).

An approximate estimate loaded by motor pressure point for each reinforcement.

of the position of the effective pivot point when the joint is is made by considering the movement of the geometric pivot When loaded by motor pressure, each reinforcement rotates

but undergoes negligible change point for each reinforcement amount, and the effective pivot

in cross-sectional shape. Consequently, the geometric pivot can be defined. Each reinforcement rotates a different point is approximately at a mean of all the geometric pivot

points.

2.1.2.3.1 Axial

Nozzle

deflection

attachment

points

Misalignment causes are

a

vectoring

a fixed

the guidance system begins the motor pressure increases.

misalignment

distance

apart,

of

as in the

the

nozzle.

case just

after

When booster

the

actuator

launch

to control the vehicle, the nozzle is not free to translate An actuator length that holds the movable components would be too short at operating the actuators were retracted (fig.

before aft as aligned

to the fixed components The nozzle at pressure

at zero motor pressure would vector as though

alignment condition

of the exit than in the

cone to the fixed components is less important in an unpressurized pressurized condition, the actuator length at zero pressure is set

minimize pressurized

the angle condition.

between the movable and the At zero pressure, this actuator

vectored as though the misalignment decreases.

actuators

were

extended.

35

pressure. 17). Since to

fixed components at some nominally length is too great, and the nozzle is As

the

motor

pressure

increases,

the

._Fixed-length

Nozzle position pressure

at

zero _/-

! ..__..I"

_41_

actuator

[ !_

i _ !. _

Axial displacement actuator brac_t

/__'--Misallgnment

!

of

an, le

, l-i'll

duetoaxi°l

...... Effective

pivot

point

"'-.

Nozzle after

position axial

"''--.

deflection"'--...j

Figure 17. - Effect of axial deflection (due to motor pressure)on nozzle alignment.

The actuator bracket (fig. 7(a)) usually is connected to the motor case; hence the actuator bracket deflects as the motor is pressurized. The effect of actuator-bracket deflection has to be

included

in determining

misalignment.

If the

actuator

bracket

is connected

to the

aft

adapter of a glass-filament-wound motor case, the misalignment due to act,6-ator bracket deflection is much larger than that due to axial deflection of the joint. This difference arises because the rotation of the aft adapter can be as much as 3 ° at maximum expected operating

2.1.2A

pressure

MEOP.

FREQUENCY

The_ movable nozzle -_ructure forms an

RESPONSE section additional

and the spring

frequency of the control system natural mode of nozzle oscillation, occurred

where

the

hydraulic

flexible in the

system. The fixed If a strong natural

applied through the actuators is near the frequency the nozzle oscillations will be reinforced. An instance

actuator

stiffness

36

/

joint form a spring-mass guidance control system.

was

low

enough

to be the primary

of a has

stiffness

determining

the

nozzle

natural

frequency.

All of the nozzle

subsystems

are designed

to have

enough stiffness so that their individual natural frequencies are high when compared with the driving frequencies transmitted through the control system. Preliminary estimates of the stiffness of each subsystem can be made, but mathematical models of the nozzle and actuation frequency

system are difficult to build without response, closed-loop damping, and

development

2.1.2.5

test data. open-loop

Consequently, damping are

tests to determine conducted early in a

program.

ENVIRONMENTAL

PROTECTION

Flexible joints are protected against exposure to hot motor atmospheres that could cause rapid aging of the elastomer. been demonstrated on a natural-rubber formulation (ref.

gases, warm atmospheres, The effect of temperature 91), the results showing

and has that

increasing temperature decreases the shear modulus, the allowable stresses and strains, and the strength of the bonds to the reinforcement. Atmospheric aging of specimens of natural-rubber formulations show increased shear modulus and reduced allowable stresses and

strains

aging

(ref,

(refs.

Limited

92).

93 and

studies

Other

studies

have

shown

that

silicone

rubber

is much

less sensitive

to

94).

(ref.

85)

with

laboratory

specimens

have

been

conducted

(1) neoprene, (2) neoprene/polybutadiene, (3) ethylene propylene butyl, and (5) silicone, for use in joints over a temperature range 165 ° F (347 K). The results showed that for all formulations (1) affected from -40 ° F (233 K) to 70 ° F (294 K) and decreases up to tensile elongation is neoprene/polybutadiene increases with decreasing

a maximum and silicone temperature,

K). The secant neoprene/polybutadiene

modulus at is little affected

shear

at 70 ° F (294 formulations showed and (2) shear elongation 50 from

psi (0.345 70 ° F (294

on formulations

of

terpolymer (EPDM), (4) from -40 ° F (233 K) to tensile strength is little 165 ° F (347 K), and (2)

K). Shear studies of the that (1) the shear strength is a maximum at 70 ° F (294 MN/m 2) shear stress K) to 165 ° F (347 K)

for but

increases significantly at -40 ° F (233 K), whereas the silicone formulation is little affected from -40 ° F (233 K) to 165 ° F (347 K). The neoprene/polybutadiene formulation was bench tested in a joint at -40 ° F (233 K), 70 ° F (294 K), and 165 ° F (347 K); the results showed torque

that (1) axial did not change

compression increased with increasing temperature, (2)the actuation from 20 ° F (266 K) to 120 ° F (322 K), and (3) with the value at 70 °

F (294 K) as a reference, the actuation torque decreased 18 percent at 165 ° F (347 K). 2.1.2.5.1 In most

Thermal cases,

the

increased

18 percent '_

at -40 ° F (233 K) and _ _ _ .... _

Protection flexible

joint

is protected

by controlling the atmosphere surrounding conducted with the joint at temperatures

against

exposure

the joint prior from 65 ° F (291

37

to warm

or cold

atmospheres

to firing. Most joint testing is K) to 85 ° F (302 K). Limited

bench testing has been conducted on joints at conditions from -40° (347 The

K) (ref. joint

F (233

K) to 165 ° F

85).

is protected

from

hot motor

gases either

by use of an insulating

boot

(fig. 7(a)),

by use of sacrificial ablative protectors (fig. 7(b)). As noted earlier, either the boot has been wrapped directly around the joint or a dead air space has separated and the boot. The wrap-around boot provides less heat-transfer barrier for thickness, boot and

because the joint.

there For

is no dead air space to act as an additional insulation the bellows-type designs, pressure relief holes through

required to balance the pressure across the boot. The vent holes allow the gas pressure to equalize during high rates of change ignition, the

so that

tearing

wrap-around

Both been

boot

is prevented.

the insulating and whether

boot requires decisions to expose the boot to the

from the high-temperature a radiation shield mounted

the exposed used. Motor

boot,

the

torque is greater more envelope.

requires

more

envelope

than

whether chamber

to use a wrap-around environment of radiant

required than

that

heating between

or a heat

char and erosion temperature, and

behavior velocity.

rubber. The boot and fixed sections

95 and 96) have material for the

as a function of strain in When a radiation shield is

and radiation shield are designed (fig. 7(a)) occurs in a stagnant around the such design,

and using a silicone rubber boot, showed only slight charring the boot needed to be thick enough to withstand only the gap between the boot and the protection shield. For the insulating of the

The sacrificial ablative protectors sufficient to provide a heat-transfer To minimize that the gap

to at

when the joint is actuated and the shape of the annular cavity is altered, there is little circumferential flow in the annulus. One

22 in. (55.88 cm) in diameter with no erosion. Consequently, radiant heating through the exposed

need to be sufficient of pressure occurring

boot (refs. 13, 14, and 23) and the protected boot (refs. designs using an exposed boot require an ablative plastic

the boot material is a silicone the gap between the movable

region. Even circumference

design

the are

motor gas stream or to minimize this heating by on either the fixed or movable nozzle components.

boot,making it necessary to know the addition to gas composition, pressure, provided, so that

This

between the boot

design.

The design of bellows design, transfer providing

of the

or

insulating the joint the same

material protected

extend barrier

is stiffer, boot.

outboard between

and

However,

thus the

the

increase

protected

in actuation boot

requires

of the elastomer rings a distance the hot motor gases and the elastomer.

in the cavity between protectors, the protectors is less than the elastomer

protectors thickness

are cross sectioned (fig. 7(b)). The

so gap

between protectors must be wide enough to prevent contact during vectoring or motor pressurization. Because there is a possible path from the hot motor gases to the elastomer, it is necessary environment

to determine the environment to the char and erosion

accumulation in the gaps anomalies in the vectoring

in the region characteristics

of the protectors of the protector

and

to relate material.

this Slag

after static firing has been noted, but this buildup did not cause response of the nozzle during firing. This result was attributed to

38

the lack of adherencebetween the slagandthe carbon-fiber/phenolic--resincompositeused for the protectors. The sacrificial ablative protector doesnot causean increasein actuation torque and requireslessenvelopethan the insulating boot with a radiation shield. All thermal protection designshave been tested successfully:the exposedinsulating boot with and without bellows (refs. 13 and 14), the protected insulating boot with and without bellows (refs. 23, 95, and 96), andthe sacrificial ablativeprotectors (ref. 25). Selectionof a design is made from a study evaluating such factors as gas characteristics(temperature, composition), gas flow (velocity, stagnation regions, pressure), envelope requirements, actuation power source, and overall system weight (actuation system, joint, insulating system)in relation to performancefactors (e.g.,range,payload, and reliability) and cost. 2.1.2.5.2 Tests

of

Aging Protection flexible

joints

using

a natural-rubber

surfaces protected from the environment changes, axial compression is reduced, change has been attributed to continued

formulation

(GTR

44125)

with

the

rubber

have demonstrated that, with aging, performance and spring torque is increased. The performance reaction of the components of the elastomer. The

spring torque increased by approximately remained constant thereafter (ref. 26).

six percent The joints

per year for 31/2 years in this program were

(ref. 97) and stored in an

atmosphere at 80 ° F (300 K) and where joints have been stored for data to be available. Similar results

approximately 50% humidity. This is the only program a sufficiently long period and in sufficient quantity for have been obtained in quadruple-lap shear and uniaxial

tensile testing 110 ° F (317

same rubber formulation; humidity for 9 months

modulus

from

of specimens K) and 90% 24 psi (0.165

The decrease in affects the nozzle nominally

of the relative

MN/m 2 ) to 30 psi (0.207

axial deflection misalignment

selected

operating

pressure

changes in joint performance made. The future performance probable

joint

life (ref.

that accompanies (sec. 2.1.2.3), since are

to

some

monitored, is compared

however, accelerated resulted in an increase

MN/m 2 ) (ref.

22).

increased spring it will change the

misalignment and projections with the motor

aging at in shear

at that

torque due to aging zero alignment at the pressure.

Currently,

of future performance are requirements to evaluate

26).

Elastomers less susceptible shear modulus and shear

to aging strength

are under development, make it difficult to

but the rigorous requirements of develop a satisfactory elastomer.

Further, the long time periods necessary to evaluate an elastomer make it difficult to assess property degradation with age for a new elastomer formulation. Accelerated aging tests at high relative humidity have indicated possible degrees of aging that have subsequently been found to be Silicone-rubber

more severe formulations

than are

aging under less susceptible

normal service to aging but

conditions (ref. 22). have a shear modulus

approximately 50% greater than that of natural-rubber formulations and a shear stress at failure approximately 50% less than natural-rubber formulations; in addition, silicones are more difficult to bond to metals.

39

A possibleadditional problem that hasbeen consideredis surface

by

either

ozone

possible exposed chlorobutyl rubber The

elastomer

showed

Such

elastomer or Hypalon

surfaces rubber.

uncured

condition

in the

a decrease

or oxygen.

in the

shear

oxidation are

coated

with

is susceptible

modulus

of

oxidation of the elastomer at its been prevented by ensuring that all

has

an

impervious

to aging.

Cured

rubber

material

A natural-rubber

of

1 psi (6895

such

as

formulation N/m 2) for

each

month of age of the uncured rubber stored at 40 ° F (278 K). The elastomer in this formulation was manufactured to as high a shear modulus as the specification allows so that if the shear modulus of the cured rubber decreased because of aging of the stored uncured rubber the formulation would for six months at 40 ° F (278

remain K) and

within if after

was

rubber

was

within

rubber

specification

the

specification. The" uncured storage the shear modulus

used,

but

if outside

rubber was stored of the cured rubber

of specification

limits

the

was rejected.

2.1.2.6 If the

PRESSURE axial

flexible

SEALING

compressive

joint

assures

that

force

due

the

joint

to motor

pressure

will seal against

is sufficiently leakage

without

high,

the geometry

the need

for any

of a special

precautions. The dimensions of the movable nozzle and joint are such that a compressive axial load is applied to the joint, the result being a compressive stress in the flexible joint that is greater than the motor pressure. Consequently, small unbonded spots and voids are tolerated. When joints are manufactured by injection molding or compression molding (sec. 2.1.6.3), unbonding cannot be detected. each

bond

line

assembled. the amount

2.1.3

can be controlled only on a sample basis, because unbonded areas For joints that are manufactured by secondary bonding (sec. 2.1.6.3),

can be inspected

for unbonding

Material

elastomer, insulating material for a given

boot, and use depends

that

seeks

techniques

as the joint

is no quantitative

to optimize

its environmental bonding system

protection, between

is being

definition

materials need the reinforcement

protection from the external atmosphere. on the motor operating requirements (e.g.,

vector angle), the environmental propellant gas velocity, atmospheric these variables in turn is evaluated cost

there

of

Selection

For fabrication of a flexible joint and selected for the elastomer, reinforcement,

and

by ultrasonic

Regardless of the manufacturing method, of unbonding that will result in a leak.

operating conditions ozone content), in a tradeoff study

vehicle

and motor

4O

The motor

to be and

choice of pressure,

(e.g., propellant gas temperature, and the envelope available. Each of involving range, payload, reliability,

performance.

2.1.3.1 The

ELASTOMERS

important

reproducibility the selected

properties

in the

elastomer

selection

are

the

shear

modulus,

shear

stress,

of these properties from lot to lot, and the ease of bonding the elastomer to reinforcement material. Since it has been demonstrated that the joint spring

torque could become zero because of axial compression, efforts determine shear properties with superimposed compression (ref. 78).

are

being

made

to

The joint spring torque is directly proportional to the elastomer shear modulus (sec. 2.1.2.1.1). In the selection of an elastomeric material, the aim is to use an elastomer with as low a shear modulus as possible and with a minimum of continued feaction of the components have been

(sec. 2.1.2.5.2), developed with

which secant

will increase shear moduli

shear modulus. (sec. 2.1.7.1)

Natural-rubber ranging from

formulations 20 psi (0.138

MN/m 2) to 35 psi (0.241 MN/m 2) at 50 psi (0.345 MN/m 2) shear stress. The low required shear modulus has presented difficulties to the elastomer formulators in preparing formulations that fulfilled the chemical stability requirement. The

shear

pressure specified

stress

in the

elastomer

is caused

by vectoring

and

usually is the more significant. Successful joints quadruple-lap shear stress (sec. 2.1.7.1) of

the requirements of shear modulus and shear stress, most joints have been of natural rubber or polyisoprene formulations. The joints of both stages of the motors are natural-rubber formulations, either GTR 44125 or TR 3005 (refs. 98

and

The

the 260-in.

all failures

(6.604

were

motor

To meet fabricated Poseidon

for

and

Of these,

having a minimum MN/m 2) have been

manufactured,

joint

tested,

pressure.

designed,

99).

and

motor

using elastomers 500 psi (3.45

m) motor

cohesive.

(ref.

22)

and

a joint

designedto

operate

at 3000 psi (20.7 MN/m 2) to + 15 ° at 300 deg/sec (ref. 14) used GTR 44125 elastomer. Required properties for these elastomers are minimum shear stress of 500 psi (3.45 MN/m 2) and secant shear modulus (at 50 psi (0.345 MN/m 2) shear stress) of 22 psi (0.152 MN/m 2) to

26

psi

(0.179

MN/m 2)

for

GTR

44125

and

18.5

psi (0.128

MN/m 2) to 24

psi (0.166

MN/m 2) for TR 3005. Actual shear strengths for these elastomers are greater than 1000 psi (6.9 MN/m 2 ) (ref. 100) for GTR 44125 and 660 psi (4.55 MN/m 2 ) for TR 3005, all failures being cohesive. m) motor (ref. motor (ref. 18). those of the

Polyisoprene elastomers have been used for the joints of the 156-in. (3.962 23), the 100-in. (2.54 m) motor (ref. 19), and an advanced dual-chamber The polyisoprene elastomers demonstrate shear properties that are equal to natural-rubber formulations but the shear modulus is greater, being

approximately used for joints

27 psi (0.186 MN/m 2) minimum. Natural-rubber when the minimum expected operating temperature

(283 process than

K). Because controls 10 psi (0.070

of the

difficulty

are maintained MN/m

A neoprene/polybutadiene between -40 ° F (233

in making to ensure

an elastomer

a lot-to-lot

with

variation

formulations have been was not less than 50 ° F a low shear

in shear

modulus,

modulus

close

not greater

2 ).

formulation has been bench tested K) and 165 ° F (347 K) at an equivalent

41

jJ

in a joint designed to operate motor pressure of 2550 psi

(17.6 MN/m 2) to + 17.5 ° at 360 deg/sec (ref. 85). Required secant shear modulus (at 50 psi (0.345 MN/m z) shear stress)

properties of the rubber were a of not more than 50 psi (0.345

MN/m 2 ) when the shear strength was greater than 600 psi (4.14 MN/m 2 ), and a secant shear modulus that could decrease linearly to 25 psi (0.172 MN/m 2) at 300 psi (2.07 MN/m 2) shear were

stress; these values achieved over most

secant

shear

Silicone

modulus

elastomer

apply over the required temperature range. The required values of the temperature range except at -40 ° F (233 K), where the

was 72 psi (0.496 formulations

MN/m 2).

that

are

satisfactory

for use in flexible

joints

from

-40 ° F

(233 K) to 165 ° F (347 K) have been developed (ref. 85), but these elastomers are difficult to bond to metals. The best bonds have been achieved with steel, but even these bonds demonstrated adhesive failures. The failure adhesive shear strength for silicone elastomers varied

from

250 psi (1.72

MN/m 2 ) to 560 psi (3.86

25 psi (0.172 MN/m 2) to 40 psi (0.276 associated with the higher strength. These applications (dimethyl silicone formulations (208 stress

allowable shear require thinner

joint

an envelope

to have

2.1.3.2

strengths elastomer

with

a cone

modulus

at -160 ° F (166 K). The induced upon elastomer ring thickness,

are less for silicone formulations, layers. The shear stress is minimized angle

yield with

of approximately

zero

have

been

fabricated

with

steel

reinforcements

important stress, which

properties

in the

selection

of

ultimate and yield tensile stress, elastomers can be bonded to

degrees

(ref.

17).

and

with

composite

the

reinforcement

as ease

material

epoxy

are

resin

compressive

modulus of elasticity, ease of fabrication, the material, and cost' of the material.

of fabrication

stresses

in

a

and

cost became

reinforcement

are

a

the dominant factor stresses are relatively

ease For

with

unbonding

between

the

in selecting materials. For low (ref. 17), and factors

important. tensile

hoop

stress

compressive hoop stress on the inner radius (sec. 2.1.5.2) vectoring. Failures in the reinforcements have always occurred stress is compressive. For joints with steel reinforcements, wrinkling

reinforcements. and 25).

reinforcements, the interlaminar shear stress is also an important property. In the selection of material depends on the joint envelope. For joints with a large cone

angle, the mechanical properties have been conical envelope joints, the reinforcement

The

shear and

REINFORCEMENTS

composite addition

such

from

joints using these by designing the

The composite reinforcements have been formed with S-glass filaments (refs. 27, 28, and 29) and S-glass filaments and phenolic resin (refs. 24 and The

varied

MN/m2), the higher modulus generally being elastomers have been used for low-temperature have a glass transition temperature at -85 ° F

K), and methyl-phenol silicone formulations, due to motor pressure is directly dependent

because the formulations

Joints

MN/m 2 ); the shear

elastomer

42

and the

on

the

outer

radius

and

a

due to motor pressure and at the inner radius, where the the failure appears as a local

reinforcement,

so that

the joint

is

no longer a pressure seal. The wrinkling proceeds circumferentially around the reinforcement in a high-frequency wavepattern. For joints with compositereinforcements, the failure has appearedas rupture acrossa reinforcement thickness(ref. 27), interlaminar shear failure between different types of lamina in the laminate (ref. 28), or compressive failure (ref. 25). Correlation of test data for metal reinforcementswith calculatedresults(ref. 17, pp. 14-48, and sec.2.1.5.2) indicates that the stressat failure is the compressiveyield stress.However, buckling as a possible failure mode cannot be discounted. The failure buckling stressis dependent on the reinforcement dimensions,compressiveyield stress,and the modulus of elasticity (sec.2.1.5.2). The reinforcement material selectedaffectsthe bond to the elastomer.Elastomersthat have failed cohesivelywhen bonded to steelhavefailed adhesivelyat lower stresseswhen bonded to aluminum. Although it has been shown analytically that aluminum could be usedas a reinforcement material, it has not been usedin any joints. Joints that were fabricated with natural-robber elastomersand either epoxy-resin composites or phenolic-resin composites have never shown failure at the bond between the reinforcement and elastomer during bench testing. The joints of the motors on both stagesof Poseidoncontain 4130 steel heat treated to 180000 psi (1241 MN/m2) ultimate tensile stress,and the 260-in. motor (6.6 m) (ref. 22) incorporates4130 normalized steel. The joints of the 100-in. (2.54 m) motor (ref. 19) and 156-in. (3.96 m) motor (ref. 23) used304 Condition-A stainlesssteel,and the joint for the advanceddual-chambermotor (ref. 18) used 17-7PHannealedstainlesssteel. All of these joints have been bench tested successfully to pressuresin excess of ultimate design requirements. The first joints with composite reinforcements used continuous hoop-wound S-glass filaments with ERL 2256/Tonox 6040 epoxy resin to provide hoop strength and stiffness (ref. 27). During bench testing, these reinforcementsfailed transverseto the windings, thus showing a need for transversestrength. The transversestrength was provided by S-glass filament mats laid up between the continuouslywound S-glassfilaments (ref. 34), the mat filaments being oriented at an angle acrossthe hoop windings (refs. 27, 28, and 29). Joints with these configurations exhibited a changein the reinforcement failure mode and an improvement in joint strength when bench tested. To reduce the fabrication costs of composite reinforcements and to improve processcontrol, joints were fabricated with closed-die compression-molded reinforcements consisting of FM 4030-190 (phenolic-preimpregnatedS-glassroving) chopped into one-inch lengths (ref. 24). These joints were bench tested and static fired. Early joints for all three stagesof the Trident I (C4) engineeringdevelopmentmotors were fabricated with reinforcements of S-glasscloth preimpregnatedwith phenolic resin (ref. 25). Thesejoints were successfullybench tested, and static firings with vectored nozzles were conducted successfully on second-and

43

third-stage motors. However, in the motor development program structural problems occurred in the reinforcements in flightweight joints. The resin systemwas changed from phenolic stiffness

to an epoxy resin, data have not been

2.1.3.3 For

ADHESIVE

test

joints

BOND with

formulation by injection

intended molding

205

and

primer

specimens overcome

The

steel

for operation or compression

even though by ensuring

adhesive

SYSTEM

either

Chemlok

layer thickness reinforcements

and no further problems occurred. Fundamental strength and generated for the composite materials used in reinforcements.

220

the that

for

composite

between molding,

adhesive.

The

reinforcement

bond

failed

at low

(sec. 2.1.6.2). Applying in which failures always

the joint

with

and

65 ° F (291 K) and the adhesive system

surfaces of the steel were carefully the material lots were of sufficient

was controlled resulted in joints system

or

secondary

a

natural-rubber

85 ° F (303 K), fabricated has consisted of Chemlok strength

levels

in steel

test

prepared. This problem was quality and that the adhesive

the same controls to composite occurred in the reinforcement.

bonding

consisted

of a primer

system

for

the reinforcements, FMC 47 epoxy resin, and Chemlok system is a high-temperature system. After the primer

305 adhesive (ref. 22). The primer was applied to the reinforcements,

the reinforcements was cured during

adhesive,

The

adhesive

formulation compression

were cured joint molding.

systefh

for operation molding, was

with this system silicone rubber dissolved cohesive

2.1.3.4 The

joint

for test

specimens between Chemlok

with

K).

The

steel plates

Shear failures with K) and -40 ° F (233

THERMAL

thermal

protection

and

an ambient-cure

this system K).

system was were

fabricated by Shear failures

for test specimens with a 75 percent Chemlok 608

adhesive

at 165 ° F (347

K) and

PROTECTION has

been

effected

either

by insulating

boots

or by

thermal protectors (sec. 2.1.2.5.1). The important properties for thermal-protection materials are a low thermal diffusivity, high heat of ablation levels anticipated in temperatures expected

adhesive,

neoprene/polybutadiene-rubber

-40 ° F (233 K) and 165 ° F (347 K), 205 primer and Chemlok 231 adhesive.

were cohesive (ref. 85). The adhesive formulation for the same environment

in methanol. at 70 ° F (294

JOINT

at 300 ° F (422

service, and in service.

mechanical

flexibility

with

minimum

char

sacrificial

the under fracture

joint strain at

The choice of insulating boot material depends on whether the boot is protected by a radiation shield (fig. 7(a)). For insulating boots protected by a radiation shield, K1255 silicone rubber has been used. For joints with exposed insulating boots, materials have been

44

DC 1255 reinforced with chopped asbestosfiller to reinforce the char layer (reL 18) and silica-filled butadiene acrylonitrile rubber (refs. 13, 14, 19, and20). All of thesematerials have performed successfully,but they haveincreasedthe joint spring torque (sec.2.1.2.5.1). The sacrificial thermal protector materials have been either S-glass/phenolic-resinor carbon-cloth/phenolic-resin composites. The molded S-glass/phenolic-or epoxy-resin reinforcements (sec. 2.1.3.2) included the protectors in the molding (ref. 24). The carbon-cloth/phenolic-resin protectors were fabricated as an integral part of S-glass/phenolic-or epoxy-resincomposite reinforcements(ref. 25). Both of thesematerials have performed successfullyin static firings (refs. 24 and 25) without causingan increasein joint spring torque.

2.1.4

Mechanical

2.1.4.1

GENERAL

A flexible-joint dozen other

CONSIDERATIONS

configuration has been flown joint configurations have been

firings (refs. mathematical

The derived

performance.

These

Torsional Effect

design from

of pressure

Reinforcement

at zero

modified

To

establish

because the

joint

the

expected

pressure stiffness

- Section

2.1.2.1.1

- Section

2.1.2.1.1

- Section

2.1.5.1

Section

2.1.5.2

thickness steel

reinforcements,

according is analyzed

a joint properties joint

the

initial

component

relationships. An improved of analyses (refs. 17, 79 through

design

to

the

results

of the

96). However, no with test results

developed preliminary

in this monograph

thickness

the preliminary-analysis finite-element methods modified

flexible joint is data, to establish

are presented

on torsional

layer

with

of a limited

relationships

stiffness

Elastomer

design

on an operational vehicle, and approximately a either bench tested or demonstrated in static

13, 14, 17 through 20, 22 through 29, 95, and equations have been developed that correlate

configurations. relationships,

For joints

Design

from simple dimensions

general for all

empirical and joint

as follows:

dimensions

are established

from

analysis is then conducted with 82, and sec. 2.1.5.3), and the joint

finite-element

analysis.

If necessary,

the

again. with

composite

of the composite dimensions.

The

reinforcements, were

elastomer

45

unknown. layer

a different A joint thickness

method

is designed and

and

number

has been

used

fabricated of

elastomer

at

layers are calculated according to proceduresin section 2.1.5.1. The reinforcements are designed according to procedures in section 2.1.5.2, maximum strength at failure being assumedto be 60 000 psi (414 MN/m 2). To establish the allowable composite strength, the joint

is pressure

tested

to

failure

without

vectoring

preliminary analysis of section 2.1.5.2 and The allowable composite strength is defined regardless allowable methods.

of the joint mode composite strength

2.1.4.1.1

Design Definitions

and

the

results

correlated

with

the

a detailed finite-element analysis of the joint. as the calculated reinforcement stress at failure

of failure. The joint design is modified in accordance with this at ultimate load conditions and analyzed by finite-element

The design of a flexible joint usually is established and then defined on the basis of the relationship between the loading conditions that will be imposed on the joint and the capacity of the joint to withstand these loads. Limit load, design factor of safety, design load, allowable load, and margin of safety to this relationship between joint loading are used Limit or

in this monograph,

load. service

-

The

limit

pressure

3-standard-deviation physical variables motor or combination Design applied

pressure)

load that

is the can

in the

specified

expected

vehicle, or (3) the maximum of 3-standard-deviation limits

quality,

and

load

load (or pressure). and the

following

maximum be

design terms that loading capacity.

to

design

or calculated occur

value

under

load

(or

-

and of the

design safety factor is an arbitrary multiplier greater thart for design contingencies (e.g., variations in material properties,

1

design

motor or vehicle operating limits and specified operating limits.

load

maximum

a

- The

stress).

the

all environmental operating limits

within load

the

defined

structure).

(or pressure)

is the product

of the limit

load

(or

of safety.

Design stress. - The design stress is the stress, in any structural element, application of the design load or combination of design loads, whichever the highest stress. Allowable

of a service

(1)

by

distributions

factor

are used with respect These terms, as they

paragraphs.

operating limits of the motor or vehicle including that influence loads, (2) the specified maximum

safety factor. -The in design to account

fabrication Design

are defined

are joint and joint

The

allowable

load

the slightest, produces joint failure. Joint failure failure, whichever condition prevents the joint Allowable load is sometimes referred to as criterion

46

(or stress) may from load

is the

be defined performing or stress.

load

resulting condition

that,

from the results in

if exceeded

as yielding its intended

or ultimate function.

in

Margin of safety. - The margin of safety (MS) is the fraction stress exceeds the design load or stress. The margin of safety MS

where

R is the ratio

2.1.4.2

DESIGN

Ideally,

the design

of the design

SAFETY safety

overall

factor

factor

All flexible-joint loads as defined

The



Motor



Vectoring



Vehicle



Handling

motor

joint. rings.

loads above.

tensile

would

be calculated

stresses

motor

modulus

load

or stress.

from

a knowledge

of the

randomness

is designed

to a safety

factor

of

there to the

sufficiently engineering requires an

of 1.5.

LOADS used in the flexible-joint The loads on the flexible

and

storage

acts

during

structural analysis (sec. 2.1.5) joint are those that result from

are

design

flight

conditions

as a crushing

pressure

tensile and compressive the compressive hoop

and

also

causes

an axial

compression

on the

hoop stresses are developed in the reinforcement stress in the reinforcements is more critical than the

....

pressure.

is dependent

As a result

of vehicle

section

the

of

the joint

accelerations

Vectoring of the joint reduces these stresses with

to the allowable

pressure

pressure

Significant In general,

or

(5)

required reliability and confidence levels. Unfortunately, of the relationship of the assumed failure criteria

of 1.25,

FLEXIBLE-JOINT

load

1

stress distributions in a joint, and the methods of analysis are not At present, a safety factor is established largely on the basis of combined with experience. As an example, if the motor specification safety

2.1.4.3

or stress

the allowable as

FACTOR

the design variables and the is insufficient understanding complex accurate. judgement

load

1 R

by which is defined

nozzle

increases the reinforcement hoop stresses on one side of the joint and on the other. Shear stresses induced in the elastomer rings increase Vectoring on strain accelerations imposes

rate

affects

the

elastomer

shear

stresses

since

the

shear

rate. during loads

on

launch, the

47

joint.

flight, These

or staging,the loads

can

mass cause

of the movable all the

stresses

induced by motor pressureor vectoring and, in addition, can causean axial tensileload on the joint. Usually the stressesdue to vehicle accelerationsare not critical conditions. Handling

and

storage

During handling joint, since such

2.1.5

conditions

and loads

Structural

The structural reinforcement

The

analysis thickness,

ELASTOMER

stresses

in the

all the

stresses

induced

by the

tensile from

previous

conditions.

loads are imposed the reinforcement.

consists and the

of the determination finite-element analysis.

to determine stresses.

internal

of the elastomer thickness, the All structural analyses consist of

stresses,

and

a strength

analysis

comparing

THICKNESS elastomer

are

caused

due to vectoring is approximately thickness of elastomer (i.e., number

by vectoring

and

constant in the of elastomer rings

motor

elastomer x thickness

pressure.

rv

=

0.01745Go

The

shear

on the joint spring due to vectoring is

Rp 0

(6)

_nte

where rv = shear

stress

due

to vectoring,

psi (N/m 2)

(eq.(1)),

Go

= secant shear modulus at 50 psi (0.345MN/m psi (N/m 2 ), at the elastomer temperatures

Rp

= pivot

radius,

0 = vector

angle,

n = number te

= thickness

Angle 0 is expressed

numerically

2 ) shear stress (sec. expected in operation.

in. (cm) deg*

of elastomer

layers

of individual in degrees,

elastomer

not radians,

layer,

in this empirical

48

stress

and depends on the total of each layer) and not the

thickness of each ring.: The induced stress due to vectoring is dependent torque, decreasing as the joint spring torque is reduced. The shear stress given by the expression (ref. 23)

and, as before

on the

Analysis

two parts: a stress analysis internal stresses to allowable

2;1.5.1

cause

storage care is taken that no axial can cause debonding of the elastomer

in. (cm) expression.

2.1.7.1),

The shearstressdue to pressureis dependentupon the thicknessof eachelastomerlayer and is givenby the expression(ref. 79)

re =

te Pc Ke Rp 2

(7)

17.5

where rp = shear

stress

Pc

= motor

Ke

= correction

Calculated

results

17). The

correction

in figure

18.

due

pressure,

have

factor

shown

factor

1°0

to pressure,

psi (N/m 2)

psi (N/m 2 ) for elastomer

that

stress,

the shear

Ke has been

derived

stress

depending

increases

from

the

upon

cone

as the cone

results

angle.

angle

of reference

n

O l.I

0.6

O 4-1 4.1

0.4 0

0.2

0

I

I

I

I

I

I0

20

30

40

50

Cone

angle

_ , deg

Figure 18. - Shear-stress correction factors related to cone angle (ref. 17).

49

(ref.

17 and is shown

_d

t_ q4

increases

The resultant pressure, i.e.,

shear

stress

Zr in the

elastomer

is the

sum of the stresses

due to vectoring

r_ = r_ + rp The

resultant

stress

is compared

shear

stress

the

been

considered

(8)

allowable

shear

The

allowable

from have

a quadruple-lap shear specimen (sec. 2.1.7.1). ignored the increase in failure shear stress due

stress in an elastomer criterion is not known. the The

increase

is a complex Until the failure

in failure

following

shear

procedure

Calculate the shear stress due to the maximum various elastomer layer thicknesses.

(4)

Calculate

the

net

(5)

Determine

the

design

(6)

Plot

axial mode

design

loading

stress

ultimate

ultimate

is

of

shear

a design using the

stress to date state of

associated whether

failure ignoring

thickness:

elastomer

due to vectoring

shear

shear

required

expected

elastomer

shear

stress:

stress

as a function

ru_t

stress

parameter, calculated

spring

torque

(sec.

rv.

rr at various

shear

for

=

operating

layer

of elastomer

the axial thickness,

rp for

thicknesses.

rr X design

to determine

pressure

safety

layer

the

factor

thickness

maximum

and

allowable

deflection is calculated and compared with

by the

The elastomer thickness may be reduced if the axial compression exceeds but the net radial thickness is maintained in order to satisfy spring torque The effect of reducing the thickness is to reduce the net shear stress and the

REINFORCEMENT

stresses

stress

it with the allowable layer thickness.

deflection, increase of the reinforcements.

2.1.5.2

shear

thickness

field, and the it is not known

elastomer

(3)

requirements. requirements, requirements.

radial

the

Calculate

the

net

to determine

measured

joints designed pressure. The

is conservative.

(2)

If axial compression finite-element methods,

these

is used

three-dimensional criterion is known,

due to pressure

minimum

All successful to superimposed

Calculate 2.1.2.1.1).

the

the

stress

stress.

to be the

(1)

compare elastomer

The

has

with

and

in the

the

number

layers,

and

affect

the

compressive

failure

THICKNESS

reinforcements

conditions,

of elastomer

each

are

caused

reinforcement

by cross

50

motor section

pressure rotates

and vectoring. but

does

not

For

both

significantly

of

\, ",\

change shape. reinforcement

Such rotation causes a bending stress distribution with tension at the outer radius and comPression on

compressive stress on outer surface, so that

the 'inner it is 0nly

radius has always been necessary to determine

13, 14, 24, 27 to 29, 101, and 102). fatigue charactei_istics and fracture stresses of equal concern.

For motors mechanics

radially the inner

greater than the tensile the compressive stress

across radius. stress (refs.

the The

on the 17, 22,

that will be operated a number of times, are considerations that make the tensile

\

The compressive reinforcements

hoop, stress (ref. 79):

due

to pressure

depends

on the

number

and

dimensions

of the

"\

ap

4087

-

Pc

Kr _2

n-1

(9)

where ap

= compressive

Kr

= correction

hoop factor

stress

due

to pressure,

for reinforcement

psi (N/m 2)

stress,

the

value

depending

cone angle (ref. 1'7). The correction factor Kr has been the results of reference 17 and is shown in figure 18. n = number

of elastomer

layers Rp

3283tr

/3,/31,/32 The

= joint

compressive

2-4

cos

of reinforcement

angles

hoop

stress

(fig.

as described

in section

from

2.1.5.1.

/3

3 + tr COS2 /3 {Rp 2 (/32 -

-- thickness

tr

determined

on the

derived

in joint,

/31 )2

_3283tr

2}

in. (cm)

12), deg*

due

to vectoring

Ov -

av is given

43950

0

by (ref.

79)

K_ £Z

(10)

n-1 Equations (9) and varied in diameter

(10) are empirical relationships from 8 in. (20.3 cm) to

relationships

not

/3,/31,

and

_2

have are

expressed

been numerically

developed in degrees,

for tensile not

radians,

51

derived from results of tests of joints that 22 in. (55.9 cm). Corresponding empirical stresses. in equation

When (9)

and

(10).

the

cone

angle

is large,

the

tensile stressesare only slightly less than the compressivestresses,but as the cone angle becomes smaller, the tensile stressdiminishes until the reinforcement is in a completely compressivestate (ref. 17). The resultant hoop compressivestressor stresses

due to vectoring

and pressure, Or

The net

stress

Failure

modes

and

bulk

or is compared for

compression.

windings only reinforcements compression.

The

allowable

(buckling material

=

the

The

failure

reinforcement

av

O'p

-k

allowable

reinforcements

is rupture fabricated

bulk

layers.

steel

with

in the

compressive

are buckling mode

stress

The

buckling

stress

in high-frequency

for composite

for metal

for

metal

on specimens slightly curved

that edge effects were negligible. thickness was varied, and different stainless 6061-T6

steel, 304 aluminum,

reinforcement

CRES and

material

reinforcements

The ratio reinforcement

of

depends

has

been

with

the

hoop

modes shear

failure

for and

mode

are

established

from

a test

surface of a joint. The column was long enough so

reinforcement materials were

dimensions

upon

waves

a function of the reinforcement and the thickness of the elastomer

stainless steel, 17-7PH aluminum. Results and

fabricated

thickness. The failure windings are interlaminar

reinforcements

1)

circumferential

reinforcements

representing the inside across the width, and the

annealed 7075-T6

properties

compressive

stress.

or bulk compression) and consequently is modulus of elasticity, reinforcement dimensions,

program conducted reinforcements were

sum of the

(1

across the reinforcement with mats and continuous

compressive

is the

i.e.,

thickness used: 301

CRES annealed of the tests shown

in

to elastomer CRES half-hard stainless correlated

figure

19.

The

steel, with bulk

compression stress has been established as the compressive yield stress (ref. 17). Tests were conducted on two joints with stainless steel reinforcements; the joints were identical except that the steel was heat treated to different yield compression stress levels. The failure pressures for the joints were different, and joint, calculated by finite-element methods, yield

stresses

The

allowable

test joints The

for the reinforcement

with

following

compressive composite procedure

the

stress

number

failed reinforcement of each equal to the compressive

materials. for

composite

reinforcements is used

the stress in the was approximately

that

to determine

reinforcements approximate

the reinforcement

(1)

Determine

of elastomer

(2)

Calculate the compressive hoop reinforcement thicknesses (eq. (9)).

52

layers stress

(sec. due

is often

the desired

established

joint

from

design.

thickness:

2.1.5.1). to

pressure

(Or)

for

various

l_/m

2

ksi

828

120

690

i00

552

80--

414

60

4.1

=

0

,-4

__

TEST

L_ GO

• 276

20

oV in.-ibf N-m

304

CRES

0 17-7 17 3ol c_s

40

138

DATA

units

units

0

7075

T6

A

6061

T6

I

I

I

I

I

2

3

4

3.32

6.63

9.95 E 1/2

t

5 x

13.26

16.58

3/4 r

1/2

t e

Figure

19. - Buckling

stress for

metal

reinforcements

as a function

of the

properties

and dimensions

of the reinforcement.

103 x

104

(3)

Calculate the compressive hoop reinforcement thicknesses (eq. (10)).

(4)

Calculate

(5)

the

thicknesses

(eq.

Determine

the

thicknesses: (6)

net

compressive

hoop

ultimate

compressive

design

the

=

or X design

buckling

Plot the function minimum

material

ADVANCED

Analysis

by

assembly, structural

The

with

test

limitations

theory

of

modified

properties, properties;

methods

hoop

the

technique

(refs.

the

finite-element

pressure

(ref.

been 80).

various

reinforcement

for various

reinforcement

for various yield

reinforcement

thicknesses

stress.

stress and intersection

the buckling stress as a of these plots is the

enough probably

to ensure that the failure results in over-strength

allows

in sections Results from

structures

to be analyzed

as an

2.1.5.1 and 2.1.5.2 analyzes the the finite-element method present a in an assembly. have shown good

results.

to account

has

stress

80 to 82)

method

load

that effects;

(1)

it is basically

(2) material

have been introduced (ref. structures such as a flexible

condition, obtained A

are

for large-deformation

during loading. Each of these in the elastomer are large strains;

motor

strains

stress

of the stress, strain, and deformation distribution of the assumptions in the method, calculated results

but depend upon the local stresses an axisymmetric loading condition, For

hoop

compressive

employed assembly.

although refinements and (3) for continuum

axisymmetric The strains

various

for

factor

the reinforcements thick However, this approach

the method forming the

complete description Within the limitations agreement

for

(Ov)

ANALYSIS

finite-element

whereas elements

vectoring

(or)

design ultimate compressive hoop of reinforcement thickness. The allowable reinforcement thickness.

It has been the practice to make mode will be bulk compression. reinforcements. 2.1.5.3

to

stress

safety

compressive

up to the reinforcement

(7)

due

(11)).

oult

Determine

stress

103) joint,

good

limitations affect the analysis of a flexible the elastomer material properties are not

correlation the

is applied

are elastic

to include nonlinear the structure must be

in the elastomer; and, although motor vectoring is an asymmetric condition.

with

small-deflection

properties

use to

54

with

axial

deflection

of an incremental the

initial

geometry;

pressure

and

loading the

joint. elastic imposes

reinforcement

and stress

deformation and

strain

distribution for that load are determined, and the shape for the next increment is established by algebraically adding the deflections to. the initial geometry. The final deflected shape is determined when the last load increment is applied; the final stressand strain distributions are obtained by summing the stressesand strains for each load increment. In generalin this analysisfour load incrementsgivea reasonablecorrelation with test results. Although the shear modulus of the elastomer is dependent upon the local stresses,a constant secantshearmodulus at 50 psi (0.345 MN/m2) shearstress(sec.2.1.7.1) is used for all loading increments. Other required properties are calculated on the assumptionthat the material is isotropic and hasa value for Poisson'sratio as closeto 0.5 as the computer can accept. Efforts to usean effective shearmodulus (sec.2.1.5.1)have been unsuccessful. For the vectoring condition, the joint cross section changes,extending on one side and compressingon the other. An analysistechnique similar to that for the motor pressureis used.Componentsof the actuator load are applied to the moving surfaceof the joint as a uniformly distributed axial loading, sinusoidally distributed shearloading, and a linearly varying bending distribution acrossthe joint diameter.An increment of loading is applied as before to determine the geometry for the next increment. The stresseson one sidewill add to the stressesdue to motor pressureand subtract on the other. Only the geometry for that sidewhere the vectoring stressesadd is usedin the next increment. The geometry for that sideis assumedto be axisymmetric, andthe loadsare applied incrementally. Final geometry and stress distribution are determined as described in the preceding paragraph;material properties aspreviouslydescribedare used. Net stressesdue to motor pressureand vectoring are obtained by algebraically adding the stressesdue to eachload condition. The strength analysisfor the elastomeris conductedby comparing the maximum principal shear stress to the minimum measuredshear stress measuredfrom a quadruple-lap shear(QLS) specimen(sec.2.1.7.1). The strength analysis for the reinforcementscomparesthe maximum compressivehoop stresson the inner radius to the allowable compressivestress(sec.2.1.5.2). 2.1.6

The

Manufacture

sequence

reinforcements, elastomer, and

2.1.6.1

of

steps

for

fabrication

development of the molding of the joint.

of adhesive

a flexible system

joint between

involves the

manufacture

of

the

reinforcement_and_.the

REINFORCEMENTS

The joint reinforcements reinforcement material,

have been fabricated by a number of methods; and fabrication method are summarized in table

55

dimensional VII.

details,

TABLE VII. - Details of Reinforcements

Average spherical Motor

radius

Rp, in.

100-1nch

14.6

156-Inch

36.8

260-Inch

Conical:

Used in Flexible

Joints on Operational

Thickness tr, in.

and Development

Material

Motors

Fabrication

method

Ref.

304

Hydroformed

19

0.040

304

Spun

23

0.700

4130

0.038

normalized

Machined

from roll ring 22

forging

58 outer radius, 54 inner radius

Poseidon

C3 first stage

13.85

0.183

4130,

180 ksi

Stamped

and machined

95

Poseidon

C3 Second stage

13.69

0.108

4130,

180 ksi

Stamped

and machined

96

Dual chamber

5.75

0.060

17-7PH

NAVORD

7.18

0.110

4130,

13.69

0.108

Hoop-wound S-glass core overlaid with S-glass cloth

Poseidon

TMC/TVC C3 modified

second-stage

annealed 180 ksi

Explosive

formed

18

Machined

from plate

14

Compression

molded

27

and epoxy resin Trident I (C4) second-stage

10.34

0.050

S-glass and carbon cloth pre-impregnated

NAVORD

IRR

3.69

Notes: 1 in. = 2.54 cm TMC/TVC = thrust magnitude control/thrust vector control IRR = integral rocket ramjet

0.140

with

phenolic

resin

Chopped resin

S-glass/phenolic

Matched-metal molded

Closed-die molded

compression

compression

25

24

Steel

reinforcements.

been formed pressure was

-Hydroformed

reinforcements

by mounting an annealed circular applied to the plate, it expanded

for the

plate into

100-in.

(2.54

m) motor

in a pressurizing fixture (ref. 17). When an ellipsoidal shape. The reinforcement

was then machined from the expanded plate and heat treated to the required The spherical radius for each reinforcement in a joint was controlled by varying to which the plate was expanded. The reinforcements for the 156-in, reduce costs, all the reinforcements

have

(3.96 m) motor (ref. 23) were formed were spun from a standard conical

properties. the height

by spinning. To preform, welded

from three standard patterns that were cut from only one standard template. After welding, the conical preforms were stress relieved and pressed onto a mandrel in a horizontal shear spinning machine. Spinning was conducted in each direction from the center. The center of the reinforcement received the least section. After spinning was completed, finish

machined.

Reinforcement

amount of cold working and remained the thickest the reinforcement inner and outer diameters were

thickness

was

controlled

by measuring

the

thickness

of the

conical preform prior to installation on the mandrel, and estimating the amount of thinning required. Thinning was accomplished by belt sanding for a predetermined time after the reinforcement was formed. This method assured that each reinforcement received the same amount of cold reinforcement. In the

260-in.

thick,

the

working

(6.6

large

m)

by

motor

diameter

shear

(ref.

resulted

spinning

and

resulted

22), although in flexible

the

sections.

in a uniform

strength

reinforcements The

were

reinforcements

level

for each

0.7 in. (17.8 were

not

mm)

spherical

sections as in all previous joints but were conical sections. Since the joint envelope was cylindrical, each reinforcement was identical and only a single set of tooling was required for all reinforcements. This design resulted in cost savings in comparison with a joint with spherical reinforcements of progressively increasing radii. The reinforcements were machined from roll ring forgings. Any distortion occurring in the finished reinforcements either due to machining or handling was easily corrected in the joint mold as a result of the flexibility of the large-diameter reinforcements. Reinforcements

for the

Poseidon

motors

were

fabricated

by

stamping

washer-shaped

into the required section; this process required a die for each reinforcement. the steel was in a normalized condition. After stamping, the reinforcements machined, heat treated to the required properties, and then final machined. results

in

distortion

of

the

reinforcements,

but

performance if each individual reinforcement 2.1.6.3). The thinner reinforcements formed forming have not exhibited this distortion. The

reinforcements

for

blank of material. The reinforcement, making

the

dual-chamber

this

distortion

has

little

At stamping, were rough This method effect

is aligned in the joint molding by hydroforming, spinning,

motor

were

explosively

formed

disks

on

from

a circular

blank was clamped over a die that had the required contour it necessary to have a die for each reinforcement in the joint.

57

joint

fixture (sec. or explosive

of the Due to

forming, the thickness of the reinforcement was 4 percent to 5 percentlessthan the blank thickness.The reinforcement was final machinedfrom the formed section. The reinforcements for the NAVORD TMC/TVC joint (refs. 13 and 14) were machined from plate material. Only a few joints wereto be fabricated, andthis method eliminated the need for expensivetooling. The plate material was in a normalized condition and the reinforcements were rough machined. After machining, the reinforcements were heat treated andfinish machined. Composite reinforcements.12-end roving glass filaments

Early composite reinforcements were fabricated with an epoxy resin (ref. 28). The reinforcement

was formed by hoop winding between two plates. This system transverse strength and was modified by overlaying the hoop-wound cloth. A better method of forming these reinforcements was

with S-901 cross section

resulted in insufficient core with $34/901 glass to "B-stage" (partially

polymerize) the hoop-wound core, lay up the cloth on the faces of the core, replace in a mold, and cure under pressure (ref. 28). In this procedure, the ERR-4205 resin system was used because this sytem could be hardened, reliquified, and final cured. The same technique and materials were used to fabricate composite reinforcements for an experimental second-stage

Poseidon

C3 joint

(ref.

In the engineering development reinforcements were fabricated broadgoods,

each

27).

program, from

preimpregnated

with

for the second S-904 glass-fiber phenolic

resin

(ref.

stage of Trident I (C4) the joint broadgoods and carbon-fiber 25).

In the

motor

development

program, however, to overcome structural problems, the S-904 glass-fiber broadgoods preimpregnated with epoxy resin. The two types of broadgoods were sewn together, into The

specific patterns, glass broadgoods

assembled in a matched formed the reinforcement,

joint thermal protection. different mold for each To reduce the cost for the NAVORD molded included

in closed-die the

this method

2.1.6.2 The

joint

joint

metal mold, and cured at 325 ° F (436 and the carbon broadgoods formed

Each reinforcement reinforcement.

and complexity IRR joint were

had

of composite made from

compression thermal

molds

protection.

(ref.

These

were cut

a different

spherical

radius,

reinforcement fabrication, chopped S-glass/phenolic-resin 24).

The

reinforcement

reinforcements

demonstrated

K). the

requiring

a

reinforcements compound

molding the

integrally feasilibity

of

of fabrication.

JOINT

ADHESIVE

adhesive

system

by compression or injection 260-in. (6.6 m) motor joint

SYSTEM may

be formed

molding, (ref. 22).

during

or it may

the

molding

be obtained

process

by secondary

58

,\

(

_

for joints bonding,

fabricated as in the

Rubber-to-metal

adhesive

high stresses the adhesive

bonds

a bond Systems

adhesive

(sec.

strength designed

unbonding thin, the

problem resulting

During

Failures

have

also

fabrication,

occurred

and

Flexible

wiped the conditions.

of joints

in the

inch

adhesive When

strength, so that have consisted

failures are cohesive of a primer and an

system has acceptance close

monitoring

(sec.

2.1.7.2),

bond

FLEXIBLE joints

have

failures

that

were

when

the

been obtained tests of each

liaison

the

do not have

adhesive

layer

is then

the

to too

thickness

was

as

with

viscosity

the

of

sufficient

by lot

controlling of material

adhesive

the

primer

suppliers. and

being

thickness be used

Thickness

adhesive,

and the time for quadruple-lap shear

strength

the to

the

of the in joint

control rate

has

at which

spraying. The material tests (sec. 2.1.7.1) and

rejected.

JOINT been

The compression technique between the reinforcements compression, balls between

attributed

in the adhesive system materials. from 3 lbf per linear inch (5.25

fabricated

by

three

different

methods:

compression

molding (refs. 17, 23, 25, and 27), injection or transfer molding (refs. 29), or secondary bonding of precured elastomer (ref. 22). A summary and disadvantages of these methods is presented in table VIII.

parts

the result was used,

N/cm).

are sprayed on the reinforcements, have been selected by conducting

all lots that

system off the reinforcement, a compression molding process

unbonding did occur. When the bond layer was below acceptable levels, and adhesive failures

adhesive

(61.25

maintaining by

these materials lots to be used

2.1.6.3

joint,

of the fabrication problems involve the adhesive system is required to

resulted from lot-to-lot variations specimens failed at values varying

adhesive requiring

obtained

tests,

In a flexible

occurred.

to 35 lbf per linear

A satisfactory adhesive layer,

peel

changes.

in this kind of system has been affected by bond layer thickness. too thick and an injection molding process was used to fabricate

testing

required. These failures For example, peel test

been

and the bulk reliability,

was not as acute but bond strength was

bench

layer

have

N/cm)

process

2.1.3.3).

the joint, the flowing rubber being unacceptable unbonded

thin a bond

to small

greater than the elastomer to satisfy this requirement

The strength of the bonds When the bond layer was

occurred.

sensitive

are imposed on these bonds, system. To ensure increased

develop failures.

the too

are

compressed

or layup

13, 14, 24, 28, and of the advantages

involves physically placing strips of partially cured elastomer as the joint is assembled in the mold. The resulting assembly of by

closing

the

mold

and

providing

molding

pressure.

During

the thickness of the elastomer layers has been controlled by inserting steel the reinforcements. In early joints, the balls were positioned at the center of

reinforcements.

As the

joint

was vectored,

9

the

balls

gouged

the

reinforcement

and

cut

TABLE VIII. - Advantages

Process

Injection

and Disadvantages

of Joint Fabrication

Advantages

molding

Processes

Disadvantages

Demonstrated production technique used to " fabricate joints for nozzles on Poseidon firstand second-stage motors. Has the potential of giving uniform rubberpad thicknesses. (However, in actual production of joints for Poseidon this method resulted in nonuniform pad thicknesses on many joints. The lack of uniformity seems to be associated with tool design and wear.)

Comparatively expensive process because of the complicated method of setup and fabrication. The tooling costs are much higher than those for compression-molded joints. Has inherent bonding problems. The elastomer must flow considerable distances over the reinforcements and end rings, and the flow of hot rubber tends to remove the primer or adhesive. This problem does not occur with silicone elastomer, because the primer/adhesive system can be precured on the components. Sometimes yields joints in which the rubber is not fully compacted in all areas. This condition results in joints that leak during the proof test and are therefore rejected.

0 Compression

molding

Demonstrated production technique used to fabricate joints for nozzles on Poseidon firststage and second-stage motors. Low-cost manufacturing process and simple low-cost tooling. Joints produced by this method are approximately 30 percent lower in cost than those produced by the injection process. When natural rubber or polyisoprene rubbers are used, excellent bonding between the rubber and the reinforcements and between the rubber

Secondary

bonding

Some difficulty with bonding and porosity attributable to the tolerance variation on calendered rubber. Some difficulty

in bonding

silicone elastomer.

and end rings in achieved.

Produces joints with very uniform nesses.

pad thick-

The rubber pads have good compaction can be inspected prior to assembly. Tooling

Spacers are required. The spacers sometimes move as a result of rubber flow, and uneven rubber-pad thicknesses can result. Furthermore, small local defects in the rubber-pad layers are created when spacers are removed.

costs are low.

and

Process has inherent

bonding

problems.

Production experience limited. To date only a few joints have been fabricated by this process.

holes than

in the elastomer. In later that of the elastomer, the

joint

and

The

injection

were

removed

after

molding

technique

that holds them the reinforcements. The

molding

in position

method

joints balls

where the width of the reinforcements were positioned at the inner and outer

was greater edges of the

molding. consists

and

selected

have been used for the same occurred have been common

then

injecting

depends joint to

simply

of stacking

rubber

from

on the

preference

design and compression

produced molding

the

reinforcements

a reservoir

into

the

of the fabricator; similar results. and injection

in a mold gaps between

both

techniques

Major problems molding. The

that three

major problems have been porosity in the elastomer, variation in the thickness of each elastomer ring, and variation in the thickness between elastomer rings. Porosity in the elastomer occurred because the elastomer could flow .easily out of the mold or into large voids

in the

minimizing Variation

mold.

This

problem

was

eliminated

clearances between metal in the thickness of elastomer

clearances variations.

by

designing

a mold

without

voids

and

parts to avoid elastomer expansion out of the mold. rings has been due to a number of causes. Excessive

in the mold to accommodate parts with Thickness variations have also occurred

excessive because

tolerances has caused thickness of movement and deflection of

the joint under the high pressures of molding. Tolerance problems are avoided if the pad thickness is controlled directly by the two metal surfaces involved; this procedure minimizes the number of tolerances involved in a worst-on-worst situation. The deflection of parts can be reduced

only

by

specifications. In Movement of the surfaces that are variations inspected uniform

stiffening

the

in an elastomer

layer

for flatness and spherical elastomer layer thickness.

was cheaper (ref. 22). As bonded to the reinforcement.

axial

correct alignment. at 5 psi (0.0345 pressure

but

for a joint

The secondary bonding technique because of a lack of sufficiently

ensure loaded

parts,

stiffening

may

be impossible

because

of design

such a situation, the deflection must be tolerated and allowed for. parts in the mold, however, has been controlled by indexing parts from self-centering, i.e., conical or spherical surfaces. To avoid thickness

was

radius

with

thick

reinforcements,

variations

and

are

the

aligned

reinforcements in the

has had limited application. It was used large facilities to cure at high temperature

each reinforcement Care was taken

was laid in the during the layup

to

ensure

good

adherence

between

to give

on a large joint and because it

mold, the elastomer of the reinforcements

An ambient cure adhesive was used (sec. 2.1.3.3) MN/m 2) axial pressure by mechanical actuators

used

mold

are

the

and the joint during cure.

elastomer

and

was to was The metal

components. Two important diagnostic aids exist in joint manufacture. These aids have assisted in the discovery of manufacturing problems and the determination of the effectiveness of corrective actions. The first diagnostic aid is molding of a joint without applying the adhesive

system

to the

metal

parts;

with

this exception,

61

the

molding

process

is carried

out

normally. After molding, the rubber is easily removed from between the metal parts and examined for thicknessand porosity. The secondaid is simply the dissection of a normal, production joint by cutting through the rubber between metal parts; the resulting pieces reveal any areaswhere the rubber-to-metal bond was unsatisfactory. This technique also showsporosity andgeneralcondition of the rubber.

2.1.7 The

Testing



flexible-joint

test

program

is conducted

to determine

elastomer

material

characteristics,

joint spring stiffnesses, nozzle operating characteristics, and nozzle failure strengths so that compliance with motor requirements is demonstrated. If new elastomeric materials are to be considered, a material characterization program is conducted (sec. 2.1.3). The test program consists of subscale testing, joint bench testing, nozzle actuation testing, static firing testing, joint

aging

2.1.7.1 The and

testing,

frequency-response

SUBSCALE

TEST

subscale test program of the bond between

of the elastomer. in the

the test

specimen

most

same

modulus, the reinforcements.

manner

of test

as the

specimens,

surfaces

of the

the

of the

in the manner

properties

used

operation, in terms

!_, -: _._

:,

_

modulus ._

Go

=

elastomer

used

in the

with the quadruple-lap of the test as follows:

shear

strain

applied stress

r

Shear

strain

_/

=

2 × length

increase

in crosshead

2 X thickness

62

flexible

shear

of pad

separation of pad

joint

(QLS)

are

specimen

stress

MN/m 2 ) shear

load

× width

must

be

if possible,

of the joint.

MN/m 2 ) shear

at 50 psi (0.345

test plates

in the joint;

the

shear

of the elastomer to the metal range of temperature in the

-

Shear

of the

for manufacture

50 psi (0.345 Shear

surfaces

reinforcements

shear stress at failure, and the bond strength These properties are measured over the

elastomer expected during The properties are defined

'

testing.

is conducted to measure mechanical properties of the elastomer elastomer and reinforcement and to evaluate aging characteristics

is fabricated

important

and destructive

PROGRAM

In the preparation

prepared

The

testing,

stress

(fig. 20).

(7.62

cm)

3 in_ 118

i/8

in.

(3.2

(2.54

nun)

•v ---- f I: Ii

cm)

(2.54

I

I

I

II

I.!. '

J

i

II

N"////A l I

in.

cm)

(3.2

n-_) I

I/I///A,_

IlI l l----I"_Elastomeric for

material

test I in.

---_

I

Figure

Even

though

sufficient properties

the

elastomer

Shear

movement. reference

modulus The secant

- Quadruple-lap

in a joint

characteristics joint instability,

determine elastomer shear tension have been conducted The

20.

motor pressure, and have been determined

of the physical pressure, overall

,

I

cm)

shear test specimen.

is subjected

to compression

and

of flexible joints and nonlinearity

if vectored

at

(the reduction in actuation torque with of axial compression), limited efforts to

the

joint

spring

torque,

to superimposed

axial

compression

deflection,

stress-strain response is nonlinear, but most analyses shear modulus at 50 psi (0.345 MN/m 2 ) shear stress;

for quality control. necessary to ensure

shear

to tension and shear if vectored at zero motor pressure, the only for applied shear loads. To improve the understanding

properties when subjected (refs. 22 and 78).

controls

I__

and

and

pivot-point

assume linearity at a this value is also used

The elastomer varies from lot to lot, and close quality control a modulus acceptance range of 10 psi (0.069 MN/m 2). In a production

is

program, the testing of each lot can indicate a relaxation of manufacturing quality control or a change in the manufacturing process. The QLS is used as a quality control tool aS well as a means to qualify new elastomers and new adhesive systems. If the aging characteristics of the elastomer are not known, a subscale test initiated early in the program. This program includes testing not only characteristics of the cured elastomer but also the effect of aging of the uncured on the resulting cured elastomer. in a program, the results of joint

'

When such effects are not determined tests are subject to misinterpretation.

63

program is the aging elastomer

and controlled

early

In evaluating the aging of uncured material storage environment and,

elastomer, at intervals,

the uncured elastomer is stored test specimens are prepared and

in the cured.

usual Tests

are conducted, and the shelf life of the uncured elastomer is determined from the results. The selected shelf life is the time during which no change occurs in the secant shear modulus of the cured elastomer. To

evaluate

stored

aging

in the

characteristics

of

environment

and,

motor

cured

material,

at intervals,

elastomer properties are plotted against time, service life of the elastomer. Properties obtained Service life testing thereafter. Results modulus When

up to 3½ years a joint

therefore elastomer

and

is injection

2.1.7.2

by testing

BENCH

joint

bench

test

then

elastomer

a subscale

test

remain the

from

program

and the results are at zero time provide

monthly intervals up to natural-rubber formulations

several

lots

conducted.

is

The

extrapolated to predict a basis for compariso/_. 6 months and annually increase in secant shear

constant. test

specimen

elastomer aging joint. The aging

full-scale

TEST

at that

molded,

the measured in the full-scale

are assessed

The

is conducted have shown

cured

cannot

be fabricated

characteristics characteristics

in similar

may differ from of injection-molded

fashion;

those joints

of the usually

joints.

PROGRAM program

is conducted

to determine

axial

compression

due to pressure,

spring torque, offset torque, sealing capability of the joint, and the location of the effective pivot point; to verify calculations; and to demonstrate structural integrity of the joint. Thus data must be obtained as early as possible in a program to confirm clearance envelopes in the nozzle continued

design. When a program for quality control.

The

compression

axial

clearance the joint

envelopes. is expected

is in the

is required

to

production

determine

phase,

the

axial

the

spring

The bench testing is conducted at the same to transmit during actual motor operation.

bench

stiffness

test

program

and

to

is

check

pressure and axial load This condition requires

as a

special test fixture, as shown in figure 21, that contains provisions for adjusting the axial load on the joint. An unloading piston is used for this purpose. The unloading piston is sized such that the net axial load on the joint at pressure while undergoing test is equal to the load load

that will be imposed on the joint during acting on the joint during motor operation

During

the

development

axial compression analyses. The

quality

program,

of joints to eliminate

are

tests,

hoop

measured.

These

in a production possible

strains

at the

data

program

low-quality

actual motor is calculated are

of the reinforcements

of value

varies

joints

64

edges

and

operation. The net gas-pressure as described in section 2.1.2.3. in checking

considerably ensure

from the

the

joint

reliability

as well validity

to joint. of the

as the of the

In one motor,

a

Unloading

piston

Flexible

joint

UnloadingA

cross

I Un loadi_J_

cross

_J"

_Pressure

_--T-""_/_

_Post

I

pis ton

bar vessel attached

pressure |

piston bar

(pressure unloading reacted

See.

to

A-A

vessel acting

on

piston by post)

Figure 21. - Special fixture for testing joint axial deflection.

stringent after the pressurized extension leakage. successfully tested.

tensile-pressure leak test was imposed. This test was an axial tensile axial compression and vectoring tests. The joint was sealed with internally, of the joint, In the

motor

passing

the pressure causing axial b_t pressure was still applied program,

this_ 'J_

leaky

_, no

joints

failures

were

attributed

pressure effective

is less than pivot point.

the motor Attempts

rejected

after

to joint

this test but,

failure

occurred

for those in the

simulating the test

The reduced pressure affects the position an unloading-piston test arrangement that

65

joints motors

end o£ the joint, is sealed _into the closure that is connected to an more axial load is applied to the

Therefore, joints are tested only up to a pressure will be applied to a joint in the motor. Consequently, pressure. to design

conducted plates and

extension. The test fixture limited the at maximum extension to check for any

A typical join t_iest arrangement is shown in figure 22. One test bucket and the other end is sealed into a flat-plate actuator arm. In this type of test, however, at test pressure joint than occurs in a motor. the maximum axial load that

test end

Of the vectors

/ /7 ,/

7 jr

Hydraulic

actuator

Load.cell

joint

1

Pressure

chamber

Figure 22. - Fixture for testing joint actuation under pressure.

_\

"\

with

the

pivot

point

joint but

have

been

must

allow

unsuccessful, the joint

because to vector

the freely

test about

arrangement its effective

must

not

pivot

point.

control

the

Proper location of the test actuator is important. It should be positioned in the test with respect to the joint as it will in the motor. Although joint spring torque is used as a design concept, the joint is not in fact subjected to pure torque. It has been shown that when the actuator was not oriented correctly to the joint, the vectoring response in the test was different A flexible

from joint

that

in the motor.

deflects

linearly

in addition

effective pivot point. Attempts have tracking one or two points on the mathematical model to determine the model does not include linear motion,

to rotating;

thus,

it is difficult

to locate

the

been made to locate the pivot point by digitally joint or joint test fixture and using a rotational instantaneous pivot point. Because the mathematical the results are inaccurate to some unknown degree

66

.......

that depends on been developed

the joint design. (ref. 91). This

directly on a photograph, thus measurements and avoiding instantaneous Most

bench

direct shows

eliminating the the dependence

photographic the position

method of the

of measurement effective pivot

has point

need to calculate the position from deflection of each calculated position on previous

positions. tests

environmental

of joints

are

temperature

85 ° F (303 K). The extremes is predicted 2.1.7.1.

2.1.7.3

A more method

STATIC

conducted

at approximately

requirements

usually

are limited

test temperature is recorded, from the elastomeric-material

FIRING

75 ° F (297 to the

range

and joint response characterization

K),

because

60 ° F (289

the K) to

at the temperature described in section

PROGRAM

During the static firing tests, measurements are taken to check the overall design and to obtain data needed to design other components that interact with the nozzle design. Measurements taken include axial compression, vectoring capability, nozzle misalignment requirements,

friction

characteristics,

The axial compression interact with another

natural

is required to check stage or equipment.

frequency,

and damping

coefficient.

the envelope requirements when the motor must During a firing, the nozzle'is vectored to various

angles up to the maximum required angle in order to check clearances between the fixed and movable portions and to check the movable nozzle envelope requirements. During this vectoring, actuator force is measured. For comparison of static firing and bench testing results, Sizing from

the nozzles

are vectored

of the correct actuator the static firing. During

at the

same

frequency.

length for nozzle misalignment (sec. 2.1.2.3.1)is determined a firing, at several times selected to give as wide a pressure

range as possible, the actuators are held at the trial length for at least one-half second. Prior to the firing, the nozzle is actuated in the motor, sufficient measurements being made to enable calculation of the vector angle per inch of actuator stroke. From a comparison of firing

and

actuator The

pre-firing length

friction

data,

the

for null nozzle

characteristics

amount position

of the

of zero-pressure at pressure

nozzle

(i.e.,

the

misalignment

is calculated

and

the

is determined. flexible

joint)

are required

for the

design

of the guidance control system. As noted earlier, friction consists of viscous friction due to the viscoelastic characteristics of the elastomer (a rate-dependent component) and coulomb friction (a rate-independent component). During static firing tests, a nozzle is vectored at different rates but at constant amplitude, and the actuator force is measured. The data are plotted as determined.

shown

in

figure

14. Both

total

67

friction

and

the

two

components

are

thus

Frequency-responsetests are madeduring a static firing by imparting to the nozzle a duty cycle that cdnsistsof a successionof sinusoidalactuations, eachof short duration andlow amplitude. These actuations are made at different frequencies established from considerationsof the control system response.Attempts havebeen made to calculate the damping coefficient from the decaying force transient that occurs at the end of a step function applied to a nozzle;however,the attemptswerewithout success,sincethe damping coefficient could not be correlated with the viscous friction coefficient calculated from actuation data.

DESTRUCTIVE

2.1.7.4

TESTING

The failure strength of a flexible joint is determined by destructive testing. Joint failure occurs as a result of motor pressure and vectoring. Currently, failure strength of a joint for combined conditions cannot be defined. A test is conducted in which pressure is increased incrementally,

the

joint

being

actuated

to the

maximum

applied

operation at each pressure until failure of a component occurs. the design ultimate pressure, and sufficient clearance envelope increased until failure occurs. The failure test is conducted testing

vector

angle

during

motor

If the joint has not failed at remains, the vector angle is as an adjunct to the bench

program.

2.1.7.5

AGING

In addition the joints

PROGRAM

to the

subscale

is conducted.

aging

Joints

program

are stored

described in the service

in section

2.1.7.1,

environment;

an aging at intervals,

program joint

for spring

torque and axial deflection (sec. 2.1.7.2) are measured. These tests are conducted at zero time (for reference), at 3 months, 6 months, 1 year, and annually thereafter. Most changes occur in the first year. The measured values for spring torque and axial deflection are plotted against life is compared

time; the results are extrapolated to determine joint with required motor life to demonstrate probability

life. This extrapolated of satisfactory service

life.

2.1.8

Inspection

The inspection of a flexible joint fabricated by injection or compression molding is difficult. No techniqugs have been successful in evaluating the quality of the elastomer or the quality of the adhesive bonds between the reinforcements and the elastomer in a molded joint. Assurance dimensional

of joint control

and adherence

quality of the

to acceptance

is obtained reinforcements, bench

by

control process

tests.

68

of the quality of all materials used, control during mold setup and molding,

For joints fabricated by secondary bonding, it is possible to check the pre-molded elastomeric pads for internal defects such as voids, inclusions and delaminations,and the bond between the reinforcement andelastomerby C-scanultrasonic techniques(ref. 22). In addition, joint quality is assuredby control of the quality of all materialsused,dimensional control of the reinforcements,and alignmentof the reinforcementsduring joint layup.

2.1.8.1 To

INSPECTION

ensure

reliability

PLAN of the

fabrication process program is conducted.

joint,

control This

a detailed

in conjunction program permits

timely repair and correction of these areas. resulting in satisfactory joints. Development following

and

comprehensive

with a detection

program

nondestructive of potential

Proper inspection of a successful

processes inspection

(2)

Evaluation of existing inspection techniques for sufficient and development of new acceptable or adequate techniques

(3)

Verification that the of the actual defects.

(4)

Establishment inspection

of the

of

both

INSPECTION practice

types

of defects

inspection

accept-reject

that

techniques

standards

require

detection.

obtain

for

a valid

each

sensitivity and accuracy when necessary. indication

type

of

or description

defect

and

is

any redundant inspection, modification of new inspections as knowledge

development

of and

existing experience

inspections, are gained

and production.

PROCESSES to

inspect

the

joint

dimensions

and

performance.

The

dimensions

inspected are those that affect joint molding, joint performance, and joint assembly nozzle. In performance inspection, the operational integrity of the joint is demonstrated. Reinforcement

each

technique.

Elimination of and introduction during

Current

are the key factors plan involves the

steps: Determination

2.1.8.2

and

and destructive test causes of failure and the

(1)

(5)

of material

dimensions

such

as inner

and

outer

diameter

and

flatness

affect

the

in the

joint

molding. The spherical radius, thickness, and concentricity affect the joint performance. The elastomer thickness and porosity can be inspected only by molding a joint without adhesive on the reinforcement surfaces. After molding, the joint is disassembled to check elastomer

thickness

and

porosity.

The

frequency

69

of

this

inspection

depends

upon

the

variation that is noted in the thickness.Radiographicinspectionhasbeentried, but the large amount of metal in the joint preventsdefinition of the bond line or elastomerthickness being defined to the required accuracy. After molding, the joint is dimensionally inspectedfor overalllength, concentricity between the end attachment rings, and end-ring to end-ring reference plane parallelism. These dimensionsaffect the overallposition of the nozzle with respectto the motor. The operational integrity of the joint is demonstratedby bench testing (sec.2.1.7.2). The significanceof thesetests is basedon the premisethat joints successfullypassingthesetests aresuitablefor assemblyin a nozzle. 2.2

LIQUID

INJECTION

Thrust' vectoring by LITVC of a rocket motor through

THRUST

VECTOR

CONTROL

is accomplished by injecting a liquid into the supersonic holes in the wall of the nozzle exit cone. The injection

exhaust produces

side thrust by a combination of effects that include the thrust of the injectant jet itself, pressures on the nozzle wall from shock waves, and pressures on the nozzle wall resulting from addition of mass and energy to the exhaust flow. These effects are illustrated in figures 23, 24, and 25. Liquid injection TVC has provided thrust side forces of 17.6 percent of axial force injectant for such

specific impulse large deflections.

spreading forces act

vector deflections as large as 10 °, equivalent (ref. 46). However, efficiency as measured

drops to about 30% of maximum at the The low efficiency at high flowrates

of the LITVC pressures around in directions different from that

to by

high flowrates required is due largely to the

the nozzle circumference, where local LITVC of the desired thrust deflection. Serious losses in

efficiency can occur if the higher pressures induced by LITVC reach the opposite side of the nozzle. This condition can be caused by very high injectant flowrates, by the injector being located

too

incomplete close to disperse

near

the

the

and mix

the

easily

added

the gain in side less-than-maximum The

maximum

efficiency

throat,

or

by

a combination

mixing and reacting of the injectant with the nozzle exit or from using large concentrated

As the injectant flow Then as the flowrate because

nozzle

(refs.

105,

106,

is increased, is increased

flow

and

forces

practical that

thrust must

on the opposite

deflection be

accepted

!

due

injecting that do

to too not

and usually reaches a maximum. decreases. This decrease occurs side of the

Thus,

maximum

angle

is limited

if the

70

1ii

Inefficiency

gas may result from injectant streams

force increases the side force

force on the injector side. flowrates (ref. 108).

penalties

both.

107).

the side further,

is creating

of

system

side

to

nozzle

force

about

is designed

that

cancel

out

can be obtained

6 ° because to

produce

at

of

the

larger

Discharge

angle

positive injecting

When upstream

Separation

Pressure or

Squib tank

valve

(for

Toroidal tank

regulator relief

shock

valve

_arated

boundary

layer

high-|

only) Gas

High-pressure

gas

tank Injectant

or

gas

mixing

generator

Injector Manifold

Gas

to

roll-control

surplus-gas

dump

nozzles (gas

or

gen. only)

Flow Burst

Figure

23.

- Schematic

of typical

meter

Bladder

liquid

injection

TVC

system

and

diaphragm

side

force

phenomena.

/exhaust-gas and

reacting

Nozzle

Shock (Wall Nozzle

pressures

exit

area increase

I00

to

60_/o

thr_ above may

normal be

as

nozzle high

static

as

507°

of

pressure chamber

and pressure)

%

Injection

orifice

_'_'_ jectant (Wall

mixture

pressures

0 above

Sheltered (pressures 40_

below

area

to 300_ normal)

B

area 0

to

normal)

A

o °r4 4J (U

A

,r4

/_/_

&J

"I

__Pressure

along

A-A

J" \

--

\._

_Pressure

....

along

B-B

"- "----..__

O ..4

,-4 i

CI Nozzle ,-4 N _q O

Injector Pressure

along

C-C

= > o

f_

Injector

Figure

24.

- Nozzle

pressure

distribution

due

?2 ¸

to

injection

of

inert

injectant

(ref.

104).

exit

i/

L

2



kN/m2 621

10°

psi

105o _9

75°

i 0.15

90 _k--_30

552

80

483

7O

414

60

345

50

276

4O

207

3O

_

°

_:_:

_/_1 _._._/\

__

__!

I

__o_

,-4

"_.

--

o.10

0

k 03 o3

O_

I/O'°kXX_k

_-/--_

' __15

I't_ _,_

e_

e = 21.81 e= 2.86 Injection

69

3,2"

°

,, I,, ",,',x_, ' : __,_._---",.>/''_ :'_ _, I00o_\\\ \ ._oo_ _ ___.._/_/_

U

138

¢=

L___

70°_

i __

.

T--__

_ 0.o5



_

Centerline

20

I0 0.oo

0 .0

2.0

3.0

4.0

5.0

Expansion

Figure 25. - Nozzle pressure _stribution

6.0

ratio

7.0

e

due to injection of reactive injectant.

8.0

9.0

o

deflections. To obtain higher deflections, larger located nearer the exit to reduce the side-force efficiency injection Liquid

of the locations injection •

has

a number

advantageous fluid through also obtained.

of desirable



fluid

with

Long-term demonstrated. including tetroxide, days in

2.2.1

System

The

the

low

objectives

parameters performance

are unique,

sizes and

as follows:

by the axial component of component makes it doubly

systems have

surplus thrust is

rapid and can produce a signal-to-force This speed is the result of the fact that the liquid injectant, and friction, and the reaction

the of

instantaneous.

in a state contained

in clean

The

aluminum

of instant readiness sealed supplies of

has been injectants

tanks.

Design

consists of a tank of injectant, liquid injectant, under pressure

valves

controlling

flow

operate

of an LrI'VC

system-design

of injectant, injector storage tank, and

effort

a source of compressed gas, tubing, from the gas, flows through tubing

on receipt

flight-control subsystem. Basic design features LITVC systems are shown in figures 27 and 28.

injectors, type liquid injectant

orifice

system during flight by jettisoning is removed from the vehicle, extra

gas is almost

LITVC systems

and these must be above. Thus, the

for various

of which

valve pintle and drive parts, inertia and move with little

exhaust

storage of These

A typical LITVC system and injector valves. The injectors.

be used, mentioned

Freon 114-B2 and aqueous solutions of strontium perchlorate. Nitrogen one of the most highly reactive injectants, has been stored as long as 75 the Titan III system (ref. 47)i Dry N204 probably can be stored

indefinitely

vehicle different

some

main motor thrust is increased on the nozzle wall. This axial

to lighten the LITVC the injectors; as weight

all moving parts-the tank bladder-have

to the

features,

Liquid injection TVC is inherently very time less than 20 msec without difficulty.

the

must effects

system at all flowrates is compromised. Effects are presented in references 46, 108, and 109.

During vectoring, the the increased pressures



injectors limiting

are

of electric illustrated

are to establish

the

in

signals

from

figure

26.

number

location and injection angle, the type the method of pressurizing the liquid

and

and shape injectant.

the Two

type

of

of the These

are established in the system-design analyses such that required vectoring is achieved at minimum weight without violating imposed constraints (e.g.,

74

Gas

generator

igniter Gas

roll

wiring

control

Gas Inj ectant Gas

\

pressurization

generator Gas Gas-generator

igniter

supply

l

tanks

_

pressure Roll

lin_

regulator control

pressure Nozzle

Clamps

--.

Liquid

Section

w ve

and

relief

control lines

Three-pintle Section

A-A

equalizing Bladder

line Skirt

Liquid

injectant

Figure 26. - Basic design features in a LITVC system.

B-B

injector

gas

Nitrogen gas vent valve

fill

i."".::." Com_n injectant _,"• ;.' _,,-gas tank

...o...,'. r,_Compressed

and

and

nitrogen

.°".':°°; '...%'

,

_Injectant ,

TVC electrical distribution

_ tlnaJneC f:nttube

/

Illl I

TVC

box battery

_/

power

_

switch "_'_"_

i __ E lec tromech anic injector valve

Figure

_Manifo ai

27. - Schematic

transfer

_ ld

drain

In j ec tant

_Nozzle manifold

Pyr o sea i

of Titan

III

76

ullage-blowdown

LITVC

system.

_

.

| I

.or-gas

i

generator

Hot-gas

pressure

relief

valve I

I

_ _r

aft

skirt

I

No

Toroidal for

tank

liquid

injectant

(a)

Side

view

Manifold Injector

orifice

(These

"sticks"

out

the

of

liquid

seals are

nozzle

for distribution

blown at

motor

ignition) ector

valve

for liquid

injectant

zle

Injector

Freon

pressure

sensing

Heat

Hot-gas

relief

va Gas

generator

igniter Hot-gas

firing

generator

I

Motor

(b)

Figure 28. - LITVC

End

aft

skirt

view

system for Polaris A3 second stage.

77

unit

shield

envelope, evaluation

response). of the

injection

pressure

2.2.1.1

SYSTEM

To

optimize

weight,

and location

in the

of an optimization study and related parameters

and such

an as

nozzle.

OPTIMIZATION

an

bulk,

The system-design analyses consist performance of injectants, injectors,

LITVC

and

system

performance

for data

a particular from

design,

known

the

LITVC

usual

procedure

components

is to compile

and

from

selected

designs provided by manufacturers. These data then are generalized in empirical equations or curves. Schematic designs representing the design alternates (e.g., type of fluid, number of injectors, and injection location) then are prepared to serve as a basis for optimization calculations. These alternates are evaluated for performance, weight, and compliance to the vehicle space envelope. For each design concept, an overall vehicle performance parameter is calculated for use in numerical evaluation; and typically has been either the payload burn. The results of the choice, injectant amount, This initial optimization considered and injector location

this parameter depends on the vehicle mission or the vehicle final velocity at the end of motor

early optimization give preliminary number of injectors, approximate reduces significantly the number

simplifies the detailed and discharge angle,

studies amount

for injection of injectant,

determinations of the injectant system pressure, and so forth. of design possibilities to be

pressure, orifice size and spacing, and the system pressurization gas

required. As the detailed studies of these items proceed, the empirical equations are improved and the optimization is repeated as necessary to improve the results. A limitation changing

of LITVC the

design

that to

is important

accommodate

design requirements. If the system performance of which is known, requirements.

Usually,

however,

the

changes being then new

design, and data scaling has to be applied of overdesign. Also, systems usually are trajectory reasons,

in the

major.redesign and operating

period

in maximum

designed the new design

are

different

and angle of the injector valves after the initial design phase and

revised

items that most tubing, injector

in

or other

any

the the

previous

and the likelihood of the worst-case

downwards.

For

these

better linearity and jet carried in the tank, are they do not necessitate influence system weight valves, and the location

on the nozzle wall) are difficult and therefore usually are left unchanged.

78

force

from

uncertainties initial estimate

in particular redesign of pintle shape to provide flowrates and to reduce the amount of injectant are made late in the development period because

and additional tests. However, the efficiency (sizes of tanks, brackets,

side

of flexibility

similar to an earlier design, can be designed close to

is significantly

estimates

is lack

required

is very system

with the attendant sized to meet the

requirements. Later these initial most systems in use are oversized.

Minor corrections, formation at lower changes that often

development

and curves preliminary

expensive

to redesign

Oversizingis minimized by repeating the optimization procedureas late as possiblebefore the systemdesignconcept is frozen. Corrected designand performance data are used, and the flight-control vectoring requirement is reviseddownward, if possible,usually by better definition of trajectory events. Thus, the more realistic the inputs in the optimization : procedure,the more nearly correct and usually lighter weight is the final systemdesign.

2.2.1.2 The

SELECTION

chief

impulse, tetroxide

OF INJECTANT

factors

considered

density, storability, and and an aqueous solution

Freon 114-B2, and operational injectants Side

in the

specific

selection

of the

liquid

injectant

toxicity. Prime candidates of strontium perchlorate;

for other

hydrogen peroxide. The basic properties are presented in table IX and discussed

impulse.

Side

specific

impulse

its

the injectant candidates

and below.

is a measure

are

side

are nitrogen are hydrazine,

characteristics

of the

specific

vectoring

of major

power

of the

injectant and is defined as the side force, lbf (N), divided by the injectant flow rate, lbm/sec (kg/s). Reactive injectants have larger side specific impulses than inert injectants. Inert injectants to 1569 solution

or

specific angles

such as Freon 114-B2 deliver N-sec/kg), while chemically nitrogen

impulses less

tetroxide

of

than

180

to

(N204)

300

0.5 ° in Titan

400

side specific impulses of 70 to 160 lbf-sec/lbm (686 reactive injectants such as strontium perchl0rate

lbf-sec/lbm

(1765

III

configurations,

(3923

N-sec/kg)

greater

than

specific location,

impulse depends on how well the design size and spacing of injector orifices,

injectant-stream Density. and

lbf-sec/lbm

significantly

are

more

to 2942 side

have

effective,

N-sec/kg)

specific

been

delivering or more.

impulse

recorded.

values

The

At for

actual

is optimized with respect injection angle, injection

side TVC N204

delivered

to the injector pressure, and

characteristics.

- Injectant

injectors

density

required.

is a major

Storage

space

influence on

on the volume

some

vehicles

has

and been

weight

of tanks,

sufficiently

preclude use of a low-density injectant. Even when storage space was available, larger tanks, piping, and injectors imposed a weight penalty that eliminated injectants from optimization studies. For this reason, the densities of injectants

piping,

limited

to

the required low-density used usually

have been approximately twice that of water. The high density has made it possible to store the injectant in compact tanks and permitted use of relatively small tubing, valves, and injectors. Thus, both weight and space on board the vehicle have been saved. ,

?

Storability.Storability of a liquid expected storage temperatures and materials it contacts. It is the measure LITVC

system

in a state

of

readiness

depends pressures of the over

both on the stability of the fluid under and on its compatibility with the tank capability of an injectant to be stored in the

long

achieved by controlling the purity of the injectant not react with the injectant and that contains reactions.

79

periods

of time.

This

condition

and by providing a tank material no trace elements that could

usually

is

that will catalyze

TABLE IX. - Basic Properties and Characteristics of Main Operational Liquid Injectants

Injectant

//

Property or characteristic

Freon 114-B2

Side specific impulse, (t) lbf-sec/lbm

70 to 160

Density, Ibm/ft 3

134.5

Freezing or crystallization point, °F

-31

Stability in storage

Reactivity metals

with

Strontium perchlorate (solution in water) ,'

Nitrogen

tetroxide

150 to 260

180 to 400

124.5, 62% solution 126.1, 72% solution

90.0

32, 62% solution 50, 72% solution

12

Very stable; nonflammable.

Solution

Stable if dry and without

sealed storage

impurities.

Inert in absence of water.

Noncorrosive to stainless steels and aluminum.

Noncorrosive in absence of water to stainless steels and aluminum

/

/

is stable in

oo O

(ref. 110). Stress corrosion with titanium (ref. 111). Reactivity

with

polymers

Penetrates

and deterio-

rates polymers.

Almost no effect on elastomers

problem

Most elastomers are incompatible with N 204 for long-term storage;

and most

other polymers (ref. 110).

some disintegrate in hours, others in days. Only nitroso compound AFE-110 and Parker compound B-591-8 are acceptable for 90-day storage (ref. 112).

Harmless on contact.

Toxicity

Fumes harmless in moderate amounts.

Solution has low toxicity. No problem with good housekeeping. Dry perchlorate is moderately toxic and irritating

Severely burns skin and eyes on contact. Inhalation of fumes can be fatal.

to the

skin. Vehicle on ,which injectant

is used

Polaris A3 second stage; Minuteman II second

Minuteman ili third stage (66% solution)

stage; Sprint first stage.

(I) Basedon test data for which injection location in the nozzle and injector geometry wereclose to optimum.

Titan I11

Studies

have

been

conducted

to

determine

the

compatibility

of

liquid

various materials (refs. 111 through 119). The results of one such study table X (ref. 120). As shown, Freon 114-B2 is almost completely

injectants

with

are summarized in inert with metals;

however, it should not be stored in metallic materials subject to corrosion, since any water contamination causes hydrolysis and subsequent corrosion. Freon 114-B2 does not affect Teflon materials but does permeate various elastomers, thermosets, and thermoplastics; it leaches plasticizer from the plastics, making them hard and brittle. Both N204 and Sr(C104)2 are reactive. Strontium perchlorate must be contained in stainless steel or titanium storage tanks. It is stable and safe at 350 ° F (450 K), but at higher temperatures it decomposes 811 K), reaction

and

storage

pressurization

temperatures,

Nitrogen

rocket

and

.gives

the

highest

or

percholorate

side

makes purity

range

for

to 1000 ° F (755

all reactive

for any

specific

to 900

crystallizing

of the

impulse

of

liquids.

liquids the

in a 62%

injectants

temperature

solution

In

comparison

that

are

and in readiness at operational pressure tetroxide has been selected for use in the

control is

of N2 04 has been

the

system. limiting

low

temperature

for

storage.

not occur either in Freon or nitrogen tetroxide. Freon K) and N2Oa freezes at 12 ° F (262 K). Strontium

with

with

here.

occur. Elastomeric materials cannot be used for and storage requirements are well established in the

water

crystallizes

out

of the

solution

at 32 ° F (273

- Nitrogen tetroxide burns on contact, and inhalation of fumes Freon 114-B2 is harmless on contact and its fumes are harmless

amounts.

At normal

mentioned

it difficult to handle. It can be stored successfully and container inertness are met; otherwise,

III post-boost

does (238

K to

with rubber that an almost explosive end of the duty cycle in systems with

problem

a problem

for up to 75 days 47 and 114). Nitrogen

Crystallization or separation 114-B2 freezes at -31 ° F

Toxicity. whereas

is not

for the Minuteman

freezing

the

present significant problems. The current practical storability in Titan III operational practice, where the LITVC system

to remain loaded a 30-day hold (refs. engine

is a potential

and degradation will Handling precautions

and do not demonstrated

Within

combines so readily has occurred near the

reactivity, however, requirements for

decomposition long-term seals. industry has been

oxidizer.

decomposition

tetroxide

operational;its only if strict

approved through

a strong

strontium perchlorate occurs. This reaction

gas-generator

The

becomes

Freon

114-B2,

strontium

perchlorate

K).

can be fatal, in moderate

delivers

50%

more

specific impulse, costs half as much, and involves fewer compatibility and storage problems. However, strontium perchlorate is moderately toxic and irritating to the skin. Care must be exercised to prevent the these saturated materials

2.2.1.3

INJECTION

In a typical formed by

perchlorate would burn

PRESSURES

LITVC system, the a convergent round

salt or solution from rapidly if ignited.

AND

INJECTION

saturating

clothing

or wood,

since

ORIFICES

liquiffis injected into the nozzle through an annular orifice outlet with a central pintle, as shown in the injector cross

81

TABLE X. -

Compatibility

of Selected

and Aqueous Strontium

Metals and Nonmetals

with Freon 114-B2

Perehlurate (ref. 120)

Materials Tested Metals

oo t-o

Nonmetals

Ti-6A 1-4V

Hypalon

4130 steel

Neoprenes

4340 steel

Polyvinyl

7505 aluminum

Thiokol ST (polysulfide)

2024

Viton

aluminum

CN and W alcohol

"A"

347 stainless

steel

Tygon ST (polyvinyi

Molybdenum

steel

Teflons

Results after 3-week exposure

Freon

Material

Metals

20

1,6, and 100

at room temperature

114-B2

No visible effect

chloride)

Sr (C 104)2

on any metal.

4130

and 4340

steels showed

some rust; other metals showed no visible effect.

Nonmetals

All specimens showed

except the Teflons

signs of permeation

deterioration.

Significant

of liquid indicates problems.

and pickup

permeability

Polyvinyl

alcohol and Thiokol

showed signs of chemical

ST

reaction

and deterioration; other specimens showed no visible effect. Pickup of liquid was negligible.

sections

in figures

29,

30, and

31. The

central

pintle

acts

as the

gate

of the

injector

valve.

Thus, the full system pressure is applied to the liquid up to the point of discharge through the orifice. The injection pressure, orifice size, and orifice spacing have a significant influence Injection through

on side-thrust

efficiency

system pressure the orifice with

because pressures 121, and

compexity. force best

that drives the liquid side-thrust efficiency.

from 450 to 1500 psi (3.10 to 10.34 MN/m 2 ). Analysis of test firings with LITVC indicates that for maximum side-thrust

injection pressure (ref. 121). Such

these pressures are used, the

system

is important because it provides the the high momentum needed to obtain

System pressures in use range data from small-scale motor efficiency the rocket motor

and

should be set at about high pressures may not

also influence the weight probable loss in side-thrust

twice the chamber pressure be optimum for the entire

of the system

of tanks, tubing, and injectors. If lower efficiency can be estimated (refs. 108,

122).

Efficient development of side force by fluid injection depends mainly on rapid mixing and chemical reaction of the injectant with the hot exhaust gas close to the wall This complex process involves droplet shattering, evaporation, and nonequilibrium chemistry. It should be noted that practically all injectants decompose and react chemically, including the so-called inert injectants, although for these liquids the energy this process and the effects that compose it are found For most efficient fully reacted with

development exhaust gas

released is small. Analytic models of in references 105, 106, 110, and 123.

of side force, the injectant should be thoroughly mixed and in the immediate neighborhood of the wall. For thorough

mixing, the liquid jets should have the highest possible However, to prevent the high-velocity jets from passing

momentum and therefore velocity. out of the immediate neighborhood

of the wall and penetrating too far into the gas stream, where their effects would be lost, the individual jets must be made so small that in spite of their high momentum they will have broken up and become mixed with the gas while still close to the wall. At all flowrates, the momentum per unit mass of liquid discharged remains about the same, since it is dependent on the pressure of the injectant in the system. This momentum contributes to the LITVC effect

by

partially injectant For

delivering

a force

against

the supersonic

stream

that

produces

the initial

shock

and

from

the

diverts the direction of flow. The balance of the LITVC effort results and its reactions producing higher flow pressures acting against the wall.

a well-designed

pintle-type

injector

(figs.

29

and

greatest side-thrust efficiency is obtained at low because at low injector openings the jet maintains discharged but the annular jet stream has a thin

30)

having

a given

orifice

flowrates (ref. 108). This effect occurs the usual high momentum per unit mass section, so that it mixes efficiently and

penetrates only into the gas that is closest to the annular jet increases in thickness, so that it penetrates

wall. At high flowrates, much more deeply into

stream, thereby must be applied

the

carrying the to be useful.

injectant

farther

83

from

size, the

wall

to which

the

however, the nozzle pressure

the gas

effects

Pintle

Erosion resistant insulation_

Injector valve

body

0

%

mechanism and hydraulic valve.operatol Nozzle

Figure

29. - Cross

section

drawing

Passages

of typical

for

fluid

single-orifice

that

powers

injector

mounted

on nozzle

injector

_njectant inlet

Orifice Pintle Nozzle

Figure

30. - Cross

section

drawing

of three-orifice

84

injector

wall

mounted

on

nozzle

wall.

wall.

Ball

screw

helical

bearing IX:

electric

torque field

Injectant

motor

inlets

J

5

/ i Pintle

position

transducer Injector

mount

Figure 31. - Cross section drawing of an electromechanical injectant valve.

Side-specific-impulse openings (ref. 108) The drop advantageous

in

efficiencies have an upper limit at very small orifice because increasing orifice friction reduces jet momentum

efficiency that occurs with to use a large number of small

large flow from orifices. The flow

jets, ,so that in spite of the great flow momentum the main stream; instead, the jets break up close the gas, vaporizes, and reacts to release energy The

large

Increasing

number the

of injectors, number

however,

of injection

add

ports

a single is divided

sizes and valve per unit mass. orifice among

the liquid does not penetrate to the wall, where the injectant that produces higher pressure

to the increases

complexity the

and

injection

the

makes it individual

deeply mixes on the

into with wall.

cost.

efficiency,

provided

that

overlap losses and cosine regions of shock pressure, not the sum of influences

losses are not excessive. Overlap losses result from the overlap of mixing, and reacting. In these regions the local pressure increase is from two separate orifices but a lesser amount, greater however

than

alone

that

for

one

orifice

(refs.

of the LITVC wall pressures around potential side force to be lost because

108

and

124).

Cosine

losses

the nozzle; this spreading opposing force components

85

result

from

the spreading

causes a portion of the cancel. These losses are

called cosinelossesbecausethe local LITVC force is diminished, for TVC purposes,by the cosineof the anglebetweenits direction andthe desiredside-forcedirection. The basic the rocket acting

liquid injection configuration has four nozzle for positive and negative pitch

between

the

simultaneously, and from these injectors.

pitch

and

yaw

planes

or more injectors and yaw control.

require

that

several

spaced Needed

equally control

adjacent

around forces

injectors

flow

the resultant force is obtained by vector addition of the control forces The use of more than four injectors (e.g., six, twelve, or twenty-four

injectors equally spaced around the nozzle) decreases the amount of fluid required, because the injectors that must provide a given control force will more likely be located closer to the direction of the required force; with more injectors flowing simultaneously, each injector will deliver

less flow

The predicted number, and

and

therefore

response of the spacing is reduced

optimization calculations contained in references 47,

2.2.1.4 The

INJECTOR

injector

AND

on the

higher

side-thrust

efficiency.

system to changes in injection to curves and equations for

(sec. 2.2.1.1). 121, 125, and

LOCATION

is positioned

will have

Examples 126.

of

DISCHARGE

nozzle

pressure or in orifice size, use as inputs in the system

such

curves

and

equations

are

ANGLE

wall (fig. 23)

at a location

and

a discharge

angle that

is optimum for the location for injection from the side force.

expected schedule of vectoring for a typical flight. The optimum is a compromise of two opposing tendencies that add to or subtract If the injection point is as far upstream in the nozzle exit cone as

possible, increased.

wall area over as the injection

the nozzle However,

injectant-augmented

portion

of the

which point flow

the pressures are augmented by injection is moved upstream, the shock wave of

spreads

out

around

and

across

the

nozzle

is the

until

it

produces a pressure on the opposite half of the nozzle that subtracts from the desired side force. This cross-interference tendency increases with rise in the ratio of injection flowrate to motor flowrate. For a very low injection flowrate, the optimum injector position on the nozzle the

wall

optimum

126). The at which expenditure

is upstream position most the

and

relatively

is downstream

close

to the

from

favorable injection point total required program

the

throat

but

nearer

for larger the

nozzle

injection exit

flowrates

(refs.

for a particular motor is an intermediate of thrust vectoring is accomplished

107 and

location with least

of liquid.

:The injector discharge (fig. 23) usually is directed 25 °. The 25 ° angle has been found to be optimum Pointing between

throat,

the liquid the exhaust

upstream at angles ranging from in subscale tests (refs. 108 and

jets upstream produces several effects. gas and the liquid jet shatters the droplets

The greater to a smaller

0 ° to 109).

relative velocity size, thus aiding

evaporation and mixing. The injectant is delivered slightly upstream of the injection point, an effect equivalent to moving the injection upstream by that amount. Directing the fluid

86

j_

jet upstream along the wall reduces the depth of penetration of the jet and keeps the injectant mixture and its higher pressures nearer the wall, where they will produce more side force. If the jet is directed too close to the wall, at angles appreciably greater than +25 ° , the beneficial effect of better mixing and improved positioning of the resulting higher pressure region is more than cancelled out by losses (ref. 125). These losses probably result from a reduction in the useful component of the injectant jet reaction force, loss in momentum of the

main

gas stream

momentum The

due

to more

in the injector

optimum

injection

due

direct

opposition

to the larger

location

usually

by the fluid jet,

diagonal

is closer

passage to the

and greater

through

throat

loss of fluid

the nozzle

than

to the

wall.

exit,

with

a value

of optimum X/L _ 0.3 being typical (X = distance from throat to the plane of the injector ports, and L -- distance from throat to exit plane). Motors with submerged nozzles do not permit injection at the optimum location, and a performance penalty is thus imposed. For the Poseidon consideration

C3 motors, the penalty was so as a TVC system, and the flexible-joint

The injection location parameter location, can be misleading when phenomena that divergence angle, LITVC effect. Since their

cause shock

In the usually

effects of injector 108, 122, and 125.

OF LIQUID

system optimization calculations, indicates the relative efficiency

amount

of liquid

the

largest

item

and

from

for specifying injection indirectly related to the

including are more

influence the calculations

location

INJECTANT

convenient it is only

parameters dimensions

angle of injection strongly in the system optimization

curves presenting the contained in references

AMOUNT

while simple and in design, because

the side force. Other angle, and mixing-path

the location and effect is included

2.2.1.5

X/L, used

large that LITVC was eliminated TVC system was adopted.

the expansion directly related

ratio, to the

LITVC side-force efficiency, (sec. 2.2.1.1). Examples of

angle

on

side-force

efficiency

are

REQUIRED

the amount of liquid required is the parameter of each design concept considered. Not only

of weight

that

must

be carried,

but

it determines,

that is the

through

its equvalent volume, the size and weight of the tubing, injectors, and tankage. The latter is usually the heaviest item of inert weight. Thus, the system design conceptJthat requires the smallest amount of injectant liquid usually is the one shown to be gtOst desirable by the optimization calculations. JJ The

amount

of liquid

very conservative of maximum extremely the flight

method expected

unlikely, including

required

depends

on

the

required

for calculating the amount vectoring requirements.

vectoring

of liquid Statistically,

since it provides for the most unfavorable the most irregular launch or separation,

87

program.

uses type the

the such

A simple

worst combination a combination

but is

of event at every stage of most severe weather and

wind shearsat all altitudes, the most eccentricpossiblealignment of vehicleweights,andthe greatestnozzle misalignment.The statistical oddsfor this worst combination usually is very small, typically lessthan 1 in 100000. This "worst-on-worst" method generallyhasresulted in overestimatesof the total side impulse required and in design of systemsthat carry grosslyexcessiveamountsof liquid. Sometimes,after flight experiencehad revealedthis fact asin the Polaris A3 program,the amount of liquid loaded in the tank hasbeenreduced,but useof an oversizedtank continued. A better method of determining the amount of side impulse and therefore the amount of liquid required for vectoring employs statistical techniquessuchasthe Monte Carlo method (refs. 47, 127, and 128). By this method, the amount of liquid required is determinedasa function of the probability that the vehicle will not run out of liquid before the vehicle operation is completed. The calculation considersa random probable requirementfor each separatepart of the vectoring program and sums eachpart to obtain the total amount of injectant required. The calculation is repeatedmany times to develop a statistical basisfor the amount of liquid to be carried. Preliminary estimatesof total sideimpulse required for vectoring have been obtained by assuminga side force of 0.02 of total axial impulse for first-stage motors, 0.01 of total axial impulse for second-stagemotors, and 0.006 of total axial impulse for third-stagemotors. In addition to the liquid that is neededfor vectoring, liquid is carried for ullage, filling of pipes andvalves,andvalveoperation; someinjectant is lost when valvesoperate,becausethe valves cannot open and close instantaneously. This unusable liquid is minimized by designingthe tank, bladder, piping, and valvesto avoid trapping liquid and to haveonly the flow volume required. Also, some valvesleak becauseof imperfect contact between the pintle and the valveseat.This leakagecanbe minimized and with good designshould be too smallto be included in establishingthe amount of liquid. The total required storage tank capacity thus includes'the liquid for vectoring plus the "unusable" liquid required for ullage, systemfill, valve operation, and possibly leakage.A typical procedurefor determining the total amount of liquid is asfollows: (,1) The

\

vectoring

requirement

is determined.

form by deflection angle and time; second, and 0.5 deg for the balance

Preferably

it is developed

e.g., 3 deg for two seconds, of the flight time. For each

1.5 deg for one deflection angle

the required side impulse is equal to the axial thrust times the deflection angle times the time required for this amount of deflection,

\\\\\,

the the

total latter

to estimate (2)

Curves scaling

in itemized

sine of the Sometimes

required side impulse and an average deflection angle are specified. In case, the maximum deflection angle is also specified, since it is needed the

injector

of estimated and replotting

size and

location.

side specific impulse versus deflection angle are developed by available data (refs. 46, 108, 109, 121, 124, 125, and 129).

88

(3) The liquid needed for vectoring each specified deflection angleis calculatedby dividing the side impulse required by the side specific impulse indicated on the curve developed in (2). The amounts of liquid thus determined for the various required anglesarethen summed. (4) The amount of additional liquid required for ullage,filling similar needs is estimated calculations, this amount liquid.

2.2.1.6

AMOUNT

of piping,

leakage,

and

and added to the above usable amount. For preliminary is sometimes estimated at 10 percent of the total usable

OF PRESSURIZATION

GAS REQUIRED

The liquid injectant in the system is kept under high pressures by gas that acts on the liquid in the tank either through a bladder (fig. 23) or piston or directly (fig. 27). The supply of compressed gas is made large enough so that when the liquid is expelled from the tank at the largest expected flowrate, its displaced volume is filled by fresh gas at a flowrate and pressure

sufficient

to ensure

that

the

system

pressure

does

not

fall below

its required

level.

The amount of gas that must be supplied to pressurize the LITVC system 'during operation usually is determined in the final evaluation of a system concept, the pressure the system and the amount of liquid to be injected having already been established. If the

LITVC

to expand pressure 2.2.1.3). required

system

into

the

is to be pressurized volume

occupied

by

by inert the

gas, only

displaced

the exact

injectant

must

amount

its of

of gas needed

be provided.

The

final

should, of course, not be less than the required injection pressure level (sec. If pressurization gas is to be generated by burning solid propellant, more gas will be than that needed for liquid displacement. The amount of gas required is the

maximum expected gas demand rate integrated over the operating time. This demand determined from the maximum expected injectant flowrate, which in turn is obtained the "worst-on-worst" severe vectoring requirements taken at all times through the operating

rate is from motor

time.

If a vectoring program requires only occasional side forces of short duration but large magnitude and if these can occur over a wide time span, the required amount of generated gas can be very much greater than that required to displace the ejected injectant. In some cases, this excessive required amount volume to act as a gas accumulator. compressed

2.2.2 The

inert

system

of the

concept

reduced by taking advantage of excess tank cases, it has been found to be better to use

gas.

Component design

has been In other

has

Design

components been

of the

developed;

i.e.,

LITVC after

89

system the

is begun

injectant

after

has been

the

optimum

selected;

the

LITVC injection

location, angle,maximum flowrate, orifice size and spacing,and systempressurehavebeen determined;the amounts of injectant and pressurizationgashavebeen calculated; and the approximate envelopeavailablefor the componentshasbeen checkedandbeenfound to be reasonablyadequate.Component design,asconsideredin the following section,includesthe detailed design of the LITVC systemas well as adaptation of the rocket motor for LITVC. The componentsof a typical LITVC systemarethe injectors, fittings and piping, tanks with or without bladders, gas supply for pressurization,meters to equalize tank drainage,and provisions for disposal of surplus injectant. The complete LITVC assembly usually is mounted around the nozzle on brackets that attach to the nozzle or the aft end of the motor. Erosion may be moderate or severeat the injectant holesin the nozzle wall, and this area may require special insulation and structure. Also, some form of heat barrier or insulation usually is required to protect the LITVC components from the heat of the exhaustplume.

2.2.2.1

INJECTORS

The injectors streamlined

are automatically operated discharge port, so that full

valves in which injection system

the valve closure is located in a pressure is effective close to the

point of release; thus high hot-gas flow in the nozzle

discharge velocity is imparted exit cone. The design of the

efficiency. A good injector velocity in order to impart

injects liquid in a linear, nondiverging jet at the highest possible high momentum to the fluid jet so that it interacts forcefully on

the

thereby

supersonic

dispersion, A range

gas

and of

stream,

mixing

sizes

and

causing

a shock

types

Variable-orifice injectors. become the most widely applications This

to

vehicle

-

of

injectors

is available

The variable-orifice used because of its

flight-control

are summarized

injector

has

a pintle

in table gate

is approximately cone-shaped, the ahnular orifice. Injector Supply piping flow resistance,

wave

and

liquid injected into the critically affects LITVC

maximum

droplet

breakup,

(fig. 23).

injectors have been designed for use on various or considered as the means of vectoring.

adaptation

to the injector

that

systems.

rocket

injector operating Design

from

control-valve

motors

for which

(figs. 29, flexibility features

of

suppliers. LITVC

was chosen

30, 31, 32, and and consequent this

These

33) has ease of

injector

in various

the

The

XI. moves

so that discharge

axially

in the port

to throttle

flow.

pintle

when moved into the exit throat it reduces or closes can be modulated from almost zero flow to full flow.

and passages usually are sized so that even at high flowrates

large enough to avoid pressure losses due to full system pressure reaches the liquid in the

injector valve and drives the jet through the orifice and into and pintle of the injector are designed with streamlined efficiently accelerated into a narrow, high-velocity stream.

90

the nozzle. The orifice approach contours so that the flow is The injector pintle is controlled

Servo

_o

6) _I_

_

_

_

_

\

Electrical

L__pSri!!!ye_

line I

.....

Control

Control valve

pressure line

kO

Feedback transducer Injector Nozzle

valve

not

shown

Actuator piston

Figure

32. - Injector

valve

assembly

with

hydraulic-powered

actuator.

_

Pintle

!

Hydraulic

Pintle

actuator

t ransducer

location

;. "

/



Injector

t

2

_D bO Electric i;:|



feedback

i/_J Injectant

i!i_ 1

Servo

torque

motor

)ply

i:;!

_:,1 i;I

Hydraulic control

valve

Control fluid

L .....

Note:

Liquid is

used

injectant as

control

fluid Electrical Liquid

Figure

33.

- Servo-controlled

injectant

hydraulic

power

connectors

supply

systems

for

variable-orifice

injectors.

TABLE _1.

Number Motor

of nozzles

Polaris A3 second

Minuteman _D

second

Number of

Number orifices

injectors

per injector

8

stage

- Chief Design Features

of

of Variable - Orifice

Angle of

Injector

injection

weight,

(fig. 23)

Ibm

25 °

4.4

(2 per nozzle) I1

on Operatioml

LITVC Systems

Operating Type of actuation

Electro-

Response

time,

Flowrate,

pressure,

lbm/sec

psig

deflection,

12.

750

0.230

60.

620

0.120

12.5

680

0.080

131

400.

800

0.022

50

signal to full

References

see

48

hydraulic

5.2

0 °

stage

Minuteman

Injectors

Electro-

49,113,130

hydraulic III

20 °

4.0

third stage

Electromechanical

Sprint

0

11.0

°

Electrohydraulic

Titan

II1

156-Inch

24

24

0 °

24.0

Electromechanical

100.

750

0.190

0 °

25.0

Electro-

158.

750

0.400

hydraulic

Note: The first five systems listed are operational; the last was tested in a development

program.

46,128,132

133

by a mechanism that provides signals from the vehicle flight

variable control.

control of the injector flow on command of electrical The control signals may be analog (variable voltage)

or digital. The valve motor may 'be electric, hydraulic, or both. Usually it is electro-hydraulic (table XI). In this case, the valve operation is controlled by a servo mechanism in which an electrically operated pilot valve is used to admit pressurized hydraulic fluid to move the valve closure or pintle injectors usually have

and thus to modulate the three orifices and pintles

orifices and pintles have electro-hydraulic systems, operate

the injectors

In

Titan

the

III

electro-mechanical

been designed the pressurized

(figs. and

32 and

NASA

actuators

flow (figs. 29 and (figs. 30, 32, and

and presumably injectant is used

system

Fixed-orifice

(ref.

could be to provide

fabricated. hydraulic

In some power to

33).

260-in. (fig.

(6.6

31).

m)

Adc

systems,

electric

the

motor

pintle position is sensed by a linear potentiometer connected adjusts the dc current so that the pintle position matches control

30). The servo-operated 33). Injectors with five

injectors

moves

the

are

operated

by

pintle

axially.

The

to an electronic the command

controller from the

that flight

47).

injector.

-On-off

fixed-orifice

development programs and have been been developed to operational status

injectors

proposed for any

have

been

tested

in various

LITVC

for use, but to date no on-off system has solid propellant motor and only one for a

liquid propellant engine (Lance). The two potential advantages of the on-off injector are high efficiency and light weight. The high efficiency is obtained if the valve gate or pintle is withdrawn fully from a countoured orifice so that the flow of liquid is not obstructed by the pintle but is accelerated and orifices must be made sufficiently

interacts small

wall

produces

where

mixing

from the modulation. (2.59 The

and

reacting

simple two-position (The Lance injector

kg/sec)

of hydrazine

disadvantage

of

greatest

wall

actuation that weighs 1.1 lbm (0.50

at 900

on-off

with the gas with maximum force. The size of the so that the jets break up and disperse close to the

psi (6.21

fixed-area

LITVC

frequency

is set outside

the

move

the

the injector The electric

injector

pintle

actuators

ranges

into the nozzle, signal is almost takes

the

flow begins when the pintle first Time for the liquid to accelerate reacting

of the

injectant

with

the

most

is that

that

weight

results

for flowrate of 5.7 lbm/sec

can be made the actuator

side-thrust

modulation

must

The resulting force pulses problems in the vehicle

can cause

time,

trouble. very rapid. The four events included pintle movement,, the movement of

typically

gas is very

94

be

produce a unless the

and the mixing and reacting of injectant instantaneous. The time for the actuator

opens and accelerates to full flow varies nozzle

light

MN/m 2).

Response time. - LITVC system response in response are the electric vector signal, liquid through in the. nozzle.

The

requires no feedback kg) and has a flow rate

accomplished by varying the length of the flow pulses. vibration effect that can cause structural or operating ,,

pressure.

15 to 200

milliseconds.

as the pintle completes from 1 to 10 msec. The

rapid,

ranging

from

less than

with gas drive to The

liquid

its motion. mixing and 1 msec

for

average-sizemotors to 2.5 msec for large motors time

is the

approximate

sum

of these

times

(note

such that

as the Titan III. The total response injectant flow and pintle movement

times overlap) and can be as little as 22 msec (ref. 139 and table time can be obtained by reducing the mass of the pintle, increasing and increasing the injectant pressure. Supplemental just upstream to malfunction.

injector hardware. - Screens of the injector to catch any

In some cases, closures storage or after system

are used activation

usually are installed pieces of solid matter

XI). A shorter response the pintle drive force,

in the liquid-supply piping that might cause the valve

at the injection orifices to prevent loss of liquid during but before motor ignition. For example, the Titan III

LITVC system is designed to be capable of being held at launch readiness for up to 75 days. The stored liquid is allowed to fill the entire system and is sealed from leakage loss at injector outlets by pyroseals sec after ignition (ref. 47).

2.2.2.2

STORAGE

The chief summarized The

liquid

TANK

AND

design features in table XII. injectant

is

(fig. 27).

of

Pyroseals

are fluid-tight

plugs

that

burn

off about

1/4

systems

are

BLADDER liquid

stored

storage

in one

or

systems

more

for

operational

spherical,

cylindrical,

LITVC

or

toroidal

tanks

typically made of stainless steel, titanium, or aluminum. Each tank usually is connected: to a system supplying compressed gas to pressurize the liquid. The gas may be cold and inert, usually nitrogen, or hot and reactive if generated by burning solid propellant. A membrane liquid and

or bladder prevent the

usually is used in each tank to keep the gas separated gas from mixing with, exchanging heat with, reacting

bypassing the fluid. It is advantageous and eliminate a development problem. and the liquid injectant are compatible tank outlet compressed

from the with, or

to eliminate the bladder if possible to reduce weight The bladder can be eliminated if the pressurizing gas and if the liquid is positively positioned over the

as in the LITVC system of the Minuteman helium to pressurize strontium perchlorate

III third stage. This system solution in a spherical tank.

uses The

gravity and acceleration forces apparently are sufficient to hold the liquid over the tank outlet. The bladder usually is a laminate of strong flexible plastic and fiber materials coated with an injectant-resistant material. Typically the internal fiber web has provided the needed mechanical strength and the facing side and an inert permeable seal bladder development, because the been critical to blow by

to the success the liquid and

plastic layers have provided thermal insulation on the gas on the liquid side. Much effort has been expended on dependable separation of liquid and pressurizing gas has

of most systems. enter the piping

95

A ruptured bladder may allow to the injectors, thus causing

pressurizing gas loss of control

TABLE XH.

Liquid

Motor

injectam

Polaris second

114-B2

Chief Design Features

Injectant density,

Amount of liquid

Liquid tank

lbm/ft 3

stored, Ibm

material

134.5

200

Aluminum

of Liquid Storage

Tank shape

third stage

Separation

on Operational

between

Toroidal

Bladder(Viton reinforced

LITVC Systems-

Source

of

pressurization

Initial

Surplus liquid

gas pressure,

jettisoned into nozzle during

psia

flight

Gas generator

NA

Gas generator

NA

Composed

3320

Yes

Dry weight of LITVC system,

139

with

Dacron)

!i

Freon

114-B2

134.5

259

Steel

Toroidal

(17-7PH)

stage

Minuteman

Systems

gas and liquid

stage

Minuteman second

Freon

A3

-

Bladder (Viton AVH reinforced with

111

Sr(Cl04)2 (62% solution

124.5

49.3

Ti-6AI-4V

Spherical

Yes

228

Dacron)

None

helium

No

42

gas

in H20 )

Sprint

Freon

Titan II1

N2 04

114-B2

134.5

160

Stainless

221

Piston

Gas generator

NA

None

Compre_ed

11O0

Yes

Cylindrical

7054

55O0

No

8808

steel

90.0

8424

Stainless

nitrogen

steel (41 O)

156-Inch

No

Cylindrical

N204

90.0

8170

Stainless steel

Cylindrical

Bladder (stainless steel and chlorobutyl rubber)

Notes: Status of systems and references for data are indicated in Table XI. NA = not applicable

gas

Compressed nitrogen gas

Ibm

effectiveness

and

system

pressure.

The

combustion of a reactive injectant. injectant in a system in which the serious result has been the reduction directly

to the

fluid

some of the best 117, and 118). A burst

and

diaphragm

have

at the

been

tank

of bladder

failure

also may

contraction obtained

outlet

of the

with

usually

gas. In bladder

laminated

is used

plastic

to seal

development

and metal

the

fluid

alternate

liquid

the

and

arrangement

pressurizing

having

gas in the

neither same

a bladder

tank

and

nor

relies

a burst

only

the

diaphragm

on gravity

work,

foil (refs.

in the

storage. On system activation, the rise of pressure in the fluid tank breaks and fluid flows through the tubing and manifold and into the injectors. A simpler

be sudden

For example, in an LITVC test using lead perchlorate bladder was eliminated, an explosion resulted. A less of the pressurizing capacity of hot gas by loss of heat

consequent

results

consequence

and

tank

115,

during

diaphragm,

stores

the

acceleration

forces to position the fluid over the outlet. The Titan III system uses this system (fig. 27). The supply tubing, the injectors, and about 2/5ths of the tank are filled with nitrogen tetroxide fluid and then pressurized by addition of compressed nitrogen gas into the remaining tank volume. Leakage from the injectors is prevented by pyroseals (ref. 47).

2.2.2.3

PRESSURIZATION

SYSTEM

High-pressure gas required to pressurize gas such as nitrogen or helium or by systems, the same gas generator is used The

compressed

gas system,

the fluid is provided either by a tank a solid-propellant gas generator (table as a source of gas for roll-control jets.

if independent

of the liquid

tank,

consists

bottle of any convenient shape, a squib valve, and a pressure pressure of the gas is from two to seven times the liquid system and XI), so that after is still greater than operation, the pressure-reducing injection liquid/gas bulk

the the

gas tank required

high gas pressure valve in order

usually is reduced to to obtain reproducible

liquid

has

been

used,

sufficient

With this _rangement, the initial injectant pressure but becomes successively less during cause a certain amount of wasted injectant also, in the case of electro-hydraulic valves variation

in injector

response

pressure

gas tank

or

valve. The initial pressure (tables X

needed, the tank pressure pressure. During motor

the liquid system pressure by a valve operation and to avoid an

pressure so high that it will degrade side-thrust efficiency tank is used (fig. 27), the initial gas pressure is made high

of the

of a metal

regulator operating

has discharged the full amount minimum system operating

of compressed XII). In some

still remains

(ref. 116). If a common enough so that after the for

effective

operation.

pressure is the same as the initial gas supply the TVC duty cycle. This reduced pressure will due to off-peak LITVC efficiency (ref. 133); operated by pressurized injectant, it will cause

time.

Usually the high-pressure tank is left filled remotely just before launch.

empty during storage and handling of the motor Otherwise, for the safety of personnel working

97

and is near

pressurevessels,the tank must be madeheavyweight with a factor of safety ranging from four to six. An advantageof pressurizingwith compressedinert gasis that no bladder or other separationis needed,provided gravity or accelerationforces constantly hold the liquid over the tank outlets for positive expulsion. The mixing of injectant vapor into inert pressurization gas and the dissolving of pressurizing gas into injectant liquid are minor problemsfor which allowancecanbe made(ref. 47). If a solid-propellant gasgenerator is used ir_steadof compressedinert gas as a sourceof pressurizationgas,the systemmay be designedwith the typical low factors of safetyusedin rocketry and also may be storable indefinitely in readinesscondition. The production of gas during motor operation dependson the burning rate of the solid propellant andthe burning surface at the moment. The generator propellant grain is shapedto provide a changing burning surface area that approximately matches the expected program of maximum demand for pressurizationgas.Accordingly, the gasgeneratorprovidesa continuous flow of gas throughout the motor operation sufficient to displacethe largest expectedliquid flow that may occur in each period of the motor operating time. Large vectoring usually is neededonly in the early part of the motor operation. Gas-generatorpropellant grains are designedto producelarge initial gasflows and relatively low flows later in the firing. Since adequategas flow must occur at all times whether gasis usedor not, significantly more gasmust be produced than is neededto displacethe total storedliquid. Whenexcess tank volume is provided to act as an accumulator, the total amount of gasrequiredcanbe reduced becausegas produced at times of low liquid flow demand will be retained for a limited time for useat times of largedemand. The surplus gasgeneratedthat exceedsthe liquid-displacementneedsand the accumulator capacity is diverted by a pressurerelief valve and releasedoverboard, preferably through small nozzles pointed aft so that thrust is recoveredfrom the unneeded gas.A screenis located upstreamof the pressurerelief valveto preventany particles of propellant or residue from enteringthe valveor the remainderof the system. The TVC pressurization system typically is activated either by firing a squib valveat the compressedgas tank outlet or, if a gas generator is used, by igniting the gas-generator propellant. In either casethe releasedpressureactsto break the tank outlet membraneseals (if the tank is so sealed) to fill the lines and injectors rapidly and then provide high momentum to the fluid jets dischargedinto the nozzleexhaustflow. An LITVC systemis not activated until about a secondbefore motor ignition; however,if the systemis activated but not launched,then the fluid and pressurizationdevicesmust be replenishedbefore another launch can be attempted. An exception is the Titan III LITVC system,which is filled with the fluid and pressurizedin the standbystate andrequiresonly electrical activation and the burning off of sealsat the injector port opening(ref. 114).

98

2.2.2.4

LIQUID

STORAGE

EQUALIZATION

When the system liquid distributed shifting excessively.

has two or more tanks, it is sometimes necessary to keep the weight of evenly between the tanks to prevent the vehicle center of gravity from A device such as an interlocked flow-drive positive-displacement pump

is used

the discharge

2.2.2.5

to equalize

DISPOSAL

from

OF SURPLUS

the tanks.

INJECTANT

LITVC systems almost always use liquid at a rate lower than that provided for in the design. This difference occurs because enough liquid must be carried for the worst possible flight control situation. Actual flight thrust vectoring requirements vary from vehicle to vehicle according penalized

to the mission requirements. by having to carry the excess

Some weight

flights of the

needing little vectoring liquid and not benefiting

would from

be the

added thrust resulting from liquid injection. To prevent this unneeded liquid from penalizing the vehicle performance as additional inert weight, provision is made to jettision this liquid and obtain thrust from it during its disposal. Flow meters are installed in the liquid lines to measure the amount of liquid used of liquid used. Flight control repeatedly compares and

signals

the

injectors

to expend

the

excess

motor thrust will be augmented expenditure of the excess liquid injectors and the rocket exhaust.

without and axial

2.2.2.6

MOTOR

Important exhaust dynamic

ADAPTATION

OF THE

advantages

of

LITVC

jet and usually does design of the nozzle.

are

liquid

thrust thrust

FOR

that

and the

an integrator sums the total amount total used with the programmed use

uniformly

around

the nozzle

so that

deflection. The vehicle is lightened is gained as the liquid leaves through

the by the

LITVC

it requires

only

light

protection

not complicate the structural design The design effort required to adapt

from

the

hot

of the motor or the gas the motor for LITVC is

simple and is limited to providing for (1) erosion in the nozzle around the injection ports, (2) shielding of LITVC system components from exhaust plume heating, and (3) possible structural reinforcement of the nozzle and motor aft end to accommodate the fixed loads of the LITVC system and the dynamic loads due to vectoring. The non-axisymmetric pressure in the nozzle due to injection must be provided for in the nozzle design. This pressure creates circumferential bending of the nozzle in a direction in which the nozzle typically has low stiffness. The exit cone diameter will increase in the direction of injection and decrease in the direction at right angles to injection. exit-cone structure may have to be increased. Provisions

for

erosion.

-

the liquid jets are injected within the injection ports

The

injection

In large

ports

into the exhaust-gas in the wall of the

99

nozzles

are the holes

of lightweight

in the nozzle

flow. The injector nozzle (figs. 29,

orifices 30, and

construction,

liner

through

the

which

are safely recessed 31). The interface

between the injector and the nozzle structure usually contains a gas-tight sealsuch as an O-ring. The wall

of the

nozzle

around

and

downstream

produce a characteristic pattern of deep grooves that begin on each

grooves side of

of the

injection

and ridges an injector

ports

erodes

(fig. 34). Typically, port and extend

abnormally

to

there are two aft (sometimes

spreading out in a V-pattern), a crescent of moderate erosion around the leading edge of the port, and a ridge of almost uneroded surface extending directly aft from the port. The chemical and gas dynamic effects that produce these effects have been studied by analysis and test The

(ref.

amount

119). of erosion

depends

on the

material. If a reactive injectant over which the exhaust-gas/injectant

such

reactivity

of the

injectant

and

the

as strontium perchlorate is used, the mixture passes usually has greater than

type

of ablative

entire wall area normal erosion;

typically, this erosion will be twice normal or more. Low-cost materials were considered for the 260-in. (6.6 m) motor, but subscale tests showed that these materials would be severely eroded

(ref.

119).

An inert injectant such as Freon if there were no injection from region

where

the

shock

The edges of holes severe erosion by downstream

edges

wave

will produce a cooling effect, and erosion will be less than the hole at all. However, at the outer edge of the mixture

contacts

the

wall,

the

through which the injectant the hot exhaust gas; this of

the

holes.

If

injection port and the adjacent nozzle The holes usually are tapered conically

erosion

erosion enters erosion

is allowed

is increased

slightly

over

the nozzle can be subject usually is concentrated to

degrade

wall, LITVC performance and are just large enough

the

geometry

normal. to very on the of the

may be reduced to accommodate

(ref. 47). the liquid

jet so that gas circulation and consequent heating in the hole will be minimized. are relatively small, having diameters less than about six times the boundary layer

Holes that thickness,

erode only moderately, because the supersonic gas stream tends to skip over the hole. However, large holes erode severely and are subject to a high rate of heat transfer on their downstream edge, because the high-velocity gas impinges against the downstream edge as if against an obstacle (refs. 134 and a large number of small orifices in efficiency. The problem of erosion overcome by making the holes as material such as graphite/phenolic. Minuteman III third-stage motors. in reference

135). This hole-size effect has provided a reason for using addition to that of obtaining greater side-specific-impulse in the immediate region of the injection ports has been small as possible, and by use of inserts of erosion-resistant This method was used in the A3 Polaris second-stage and Data on erosion of nozzle liners due to LITVC are given

119.

Thermal protection of LITVC system. - The LITVC system must be protected from heating by radiation and sometimes by gas circulation from the rocket jet plume. In some instances, this heating has been sufficiently great that liquid in unprotected tanks and tubing boiled,

100

! _

_iiiiii

ii

i iii_i_!ii¸¸

i

i i_

i ii!ii

i!i¸¸_¸ii¸_i_i¸ii

ii_ii!i_i il_

i i iiii_i

ii_ • _iiiiiii_i_ ¸_¸i i_iii!

!

i_i_%_i_i_i

'_,_,_'_ii_'," _'_"_ __i,,_i_!,_i '

iiiiiiii_i_iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii!!ii!iiiii!!_!_

10t

control

circuitry

burned

and

malfunctioned,

However, the problem is easily solved, weak or negligible gas flow. Adequate as a thin layer plume and the Structural transmit mount motion

the

of sheet cork or rubber. Sometimes LITVC components (fig. 28(b)).

reinforcements.load to the

The LITVC nozzle, the motor

the entire LITVC system between the nozzle and

from

a fraction

lines

of an inch

or expansion

The dynamic nozzle. The

and

joints

bracketry

and

pressure

vessels

failed.

since the heating is passive and accompanied by only protection has been obtained by light insulation such a panel

system aft end,

is installed

between

the exhaust

is usually, supported by brackets or both. Generally, it is advantageous

that to

on the nozzle in order to avoid any problem of differential the motor aft dome or skirt. Such movements have ranged

to several

inches.

When

nozzle

mounting

is not possible,

flexible

are provided.

loads caused by liquid jet produces

LITVC are a reaction

the direct result of injection of liquid thrust like a small rocket motor. This

into the reaction

amounts to a significant fraction of the total side force. It is withstood by the injector mounts to which the injectors are bolted and the adjacent nozzle structure.The emerging jet both blocks and mixes with the flow to produce a pattern of local loads on the nozzle wall (figs. The

23, 24, and 25). character

of this load

can be best

understood

by

considering

the

nature

of the

liquid

injection effect in detail. Close to the hole, the jet acts like a solid object in blocking the main flow. A detached bow shock forms upstream of each jet and causes a large and abrupt increase in wall pressure upstream and along the sides of each injection port. Fluid dynamic shear breaks the drops of liquid into tiny droplets that rapidly evaporate and mix with the exhaust

gas. This mass,

thus

added

and mixed,

increases

the

density

and

pressure

in the

local

gas flow. If the liquid is chemically reactive, it adds thermal energy to the local portion of the main flow, which further increases its pressure. In either case, this portion of the exhaust flow that has been augmented by liquid injection expands and accelerates in a manner

similar

to,

but

more

energetically

than,

the

rest

of

the

exhaust

flow.

It

thus

undergoes a greater change in local momentum than do normal (unaugmented) portions of the exhaust flow, and this change is transmitted to the nozzle wall as increased pressure. The increase of wall pressure due to addition of injectant mass and energy to the gas stream travels

with

the

flow

all the way

to the nozzle

exit,

spreading

out in a broad

fan-shaped

(fig. 24). The

forces

area , ;

described

combine

to

produce

the

total

thrust

vector

control

force

caused

by

liquid injection. If the liquid is reactive, the total side force is 11/2 to 3 times greater than that produced with an inert injectant. The increase is due to higher pressures resulting from reaction of the injectant with the gas. Comparative breakdowns of these effects are shown in table

XIII.

A method wall

that

is presented

has been

used

in reference

for estimating 136.

LITVC

these operation

102

forces

and

produces

their

distribution

asymmetric

on the nozzle pressure

loads

on

Table XIII. -

Side Force Composition

for Inert and Reactive Injectants

(refs. 124 and 127) i

Percent of total side force Side force component Inert liquid

Reactive liquid I

i

a

Reaction thrust of the fluid jets

15 to 30

5 to 15

Pressure from shock waves

25 to 50

l0 to 30

Pressure from addition of mass

20 to 50

60 to 85

and energy to the exhaust flow

the nozzle equal to the vectoring side force. These loads usually are widely distributed and cause stresses that are not significant increases to the stresses due to symmetric gas flow. Other load conditions, including handling and assembly, ground level thrust, altitude thrust, vibration, withstand loads due wall exit

and thermal loads, result in exit-cone asymmetric LITVC loads. However, to LITVC are usually the primary loads cones

designed

for minimum

It is general practice to predict Pertinent test data are then used those for erosion, calculations. The ensure

operating

and sometimes results of the

Performance

Use

test

of

than adequate to the asymmetric nozzles with thin-

weight.

the heating, to check the

erosion, accuracy

and load conditions by calculation. of the calculated results, particularly

to evaluate the validity of empirical constants used in the analyses are used to modify the design, if necessary, to

integrity.

2.2.3

conceptual

designs that are more as mentioned previously, for large-expansion-ratio

data design

Evaluation

dominates

all

to full-scale

operation,

phases

and Testing

of

LITVC

because

103

the

performance technology

analysis of the

from

LITVC

the

effect

early is still

basically empirical. Early in a

development effort, data are obtained from the literature. These data are generalized by nondimensionalizing, cross-related by plotting, and then are transformed to the new operating conditions by use of relationships based on physical laws. This method results in some unavoidable errors. Later, subscale tests are conducted to provide Finally,

data the

under conditions full-scale rocket

capability is demonstrated. the LITVC system operates

2.2.3.1

PERFORMANCE

In the early being made

data

usually

are similar is tested

to those with its

Operating-capability as designed.

DATA

stages of the to determine

performance

that motor

FOR

tests

are

of the LITVC

particular system,

routine

procedures

to ensure

that

DESIGN

development the general

period when optimization configuration of the motor

available

design problem. and its vectoring

are

those

generated

and tradeoff studies are system, the only LITVC

in previous

LITVC

development

programs. Data from at least ten LITVC development efforts are available (refs. 46, 48, 50, 51,107, 109, 121, 122, 124, through 127, 129, 133, and 137 through 142). These data usually are reduced to standard plots and correlations (sec. 2.2.3.2) for comparison with the particular The

motor

methods

being

designed

and

and

correlating

of plotting

for generating LITVC

performance data

estimates

generally

involve

for new converting

systems. the

data

and parameters to dimensionless ratios that eliminate factors of secondary importance LITVC (e.g., the parameters of the main rocket motor). Thus, thrust vector capability

for is

expressed as side-force specific impulse, the thrust vector deflection is the ratio Fs/Fa, and the injection rate becomes the ratio of injectant flowrate to nozzle exhaust flowrate. Similarly, the location of the injection port in the nozzle is expressed as the ratio of its distance from the throat to the distance from the throat to the exit (X/L). In the resulting plots (figs. 35 different basic

through 42), different efficiencies; the upper

sets of data appear as different curves and curve invariably indicates the more efficient

represent injectant

or condition. The side

most force

a form

popular and generally useful to axial force or deflection

that

(sec.

2.2.1.5).

The

next

angle) plot that weight

is ready

most

versus

the

for

use

plot is that angle (figs.

in estimating

common

plot

presents

ratio

of injectant

the

the

of side specific impulse versus the ratio 35, 37, and 42). The data are presented fluid

ratio

flowrate

of side

and,

consequently,

is useful

conditions.

104

of analyst, that have for

and

force

to exhaust-gas

is not as convenient for use by the designer it reduces the scatter in data from motors flowrates

required

comparing

the

to axial

flowrate

maximum

force

(figs.

36

(or and

of in

flowrates

deflection 38).

This

but has the redeeming feature varying chamber pressures and data

from

diverse

sources

or

160 i

I

O_

Freon

O

X

I14-B2

injectant

\ 14(

o o

\

!

Z v

\

E .o

\ 120

o !

i i

_o

\\ i00 °_

°_ U_

O.

8C

4-I

O

6C 0

0.02

L

I I°

0o

,_Data

band of full-scale

Polaris firings

e = 14 X/L= 0.3 • = 0° Pinj=

500-750 Ibf/in.29 (3,447-5.171 MN/m-)

0.04

0.06

I 2°

I 3°

_Small data

0.08 I 4°

I

scale, F a = 1080 Ibf from LOX/RP-I motor

e = I0 X/L= 0.3 • = 0° Pinj = 750 Ibf/in_ 2 (5.171 MN/m _)

Figure 35, - Comparison of small-scaleand full-scale data on injectant specific impulse vs deflection angle and side force (ref. 121).

105

Fs/F a 0

(4804

N)

0

Fs/Fa

Constant 60_

area

pressure,variable

Pinj = 750

50

Pc = 728

injection Ibf/in'2

(5.171

MN/m 2)

N204

Ibf/in. 2

e=

8

Six

orifices

(5.019

MN/m 2)

_

j

NaC 104

7_/o H202

/

NaC I04

50?0 H202

/

NaC i04

307_ H202

40_

30_

Motor parameters (except for N_O 4) P = 375 Ibf/in.2( 2.586 MN/m_)

O /

Freon

e a

jo j 2°

= I0 = 17.5 °

F a = 1080

(4804.1

Wa = 4.0 Ibm/sec d

= 1.50

N)

in.

(1.814

(3.81

kg/sec)

cm)

t Pamb=l.5

ibf/in. 2 (10.342

LOX/RP-I

propellant

kN/m 2)

--

Injection

00

Ibf

--

/ 10

C

I14-B2

parameters

_nj = 2.45 X/L = 0.3 @ = 0°

_

0

0.04

0.08 Injectant Exhaust-gas

Figure 36. - Comparison

O. 12

0.16

Triple

orifice OLo.5 i(1.27

flowrate flowrate

of performance

of inert and reactive

injectants

(data from

refs. 121 and 142).

in. cm)

300

!

Sr

(CI 04) 2 injectant 6.

.

6

E .m ,--4

-j %

cO

'

I i

260

u_ ,m

_ _ 24o "_

x

L

220

-I

_ 2oo _z ---__. 180 ¢ = 25 ° o -.j 160

¢= 0o 140 0.3

0.35

0.4

0.45

0.5

0.55

2.18

2.45

2.73

3.04

3.35

3.68

X/L

6inj 2.14

2.26

Data

at

2.34

a constant jet

Figure

37. - Effects

of injection

2.42

F /F value s a deflection angle

location

2.51

of of

0.026,

which

2.59

M. znj

corresponds

to a

1.5 °

and angle on injectant

specific

impulse

(ref.

108).

Fs/F

0

a

m

I Sr

1 (Cl

1

04) 2 [

I

injectant f

\



\ 5o_

4 ° _

//

3o_

b

\

f f

\

/

0

=

Pinj

/_

Pinj

Mmlm2)

1500 Ibf/In. 2 (10.34 I 800 Ibf/in. 2 (5.516

=

MN/m2)

/

2° -

Y

io_

0 O_ 0

0.I

0.2

0.3

0.4

0.5

0.6

Injectant

P

= c e =

800

a =

20 °

F a

=

Wa =

Figure

38.

2 (5.516

Injection MN/m

2)

7.4

7.9

- Effect

_nj

=

X/L=

ibf

(8896

Ibm/sec

of

injectant

N)

(3.583

i .0

parameters

2.45 0.35

=

2000

0.9

flowrate

parameters

Ibf/in.

0.8

flowrate

Exhaust-gas

Motor

0.7

25 °

Single

orifice

injection

kg/sec)

flowrate

and

108

injection

pressure

on

side

force

(ref.

108).

Fs/F a

0

I Freon

i13

injectant

4 °-

04

2 ° --

O-i o --

00 --

i

0

0.2

0.4

0.6

0.8

X/L

Pinj

=

do/d t Single e = i0 Pc _=

Figure 39. - Effect (adptd.

=

variable

=

Ws/Wa

=

0. i

A

_s/_a

=

0.2

_s/_a

= 0.3

_s/X_a

=

0.073 orifice

375 0°

of injection from

O

Ibf/ino

injection 2

(2.586

MN/m 2) <>

location

and orientation

ref. 109).

109

on side force for different

0.4

injectant

flowrates

140

!

!

Freon

I14-B2

injectant

r-4

Constant

O

injectant

flowrate,Ws/W

I

! tH #m

12C

e = l0

a

: 0.05

Original

data

'

I /

/ I i00

/

/

m 40

v

Transformed 40 O O

data

8O

=

60 400

0

800

Injection

:

_e

e =

e =

The

aata

the

: ein j: _

Pinj(e=7)

were

2 2)

P

= 0° =

c

used

to

calculate

the

I0 2.4 2

375 ibf/in. (2.586 MN/m

values

2)

for

relation

injection

pressures

were

= (Pinj/Pc_=loX

Figure 40. - Transformation (adptd.

145)

25 °

I0

7 by

2 (MN/m 2 x

_me

= 800 ibf/in. (5.516 MN/m

2OO0

1600

2.1

_:

The

pressure,lbf/in.

7

einj: Pc

1200

from

related

110

the

expression

Pc(e=7)

of data on injection ref. 121).

by

pressure vs injectant

specific

impulse

900

I

I Freon

I14-B2

I

800

injectant

I 3

annular

I orifices_

/

700

600 OO

o

_One

ann_u lar

orifice

50O z v

/

4OO U O

300 Note:

°rq

Orifices

circumferential

located line

on

on

a

nozzle

wall

200

I00

/ 2

0

4 Injectant

6 flowrate

(kg/sec

Figure

41.

- Effect function

of

number

x

Ws'

111

I0

ibm/sec

2.2046)

of annular

of injectant

8

flowrate

orifices (ref.

on side force 124).

as a

12

240

Sr

(CI

injectant

04) 2

Contoured Pinj

r-. o_ o

0-__

200

0

_,

Minuteman

= 750

X/L

nozzle

e = 23.5, e i= 12.5 Pc = 500 11 _in. 2 (3.447 Fa

X

_

i

=

16 001

= 290'

Ibf 2 =

data

= 0.55

(71.17

MN/m 2 ) kN)

16°

--E

o0

160 l

Design

z

cur

v

0

Pc = 400 ibf/in. 2 _2.758 MN/m 2) Pinj = 800 ibf/in. (5.516 MN/m 2)

_Q

_ i

X/L = 0.5, _ =25 ° , ein_ = 6.5 _ i = 330, _2 = 230

120

Ibf/in.

2 (10.342

MN/m 2)

bO 80

P

I

"

I

le

da_! _'_

_

--..nj =

,4

o arls

conzca

nozz

e

a a

_.._.........._._

O

.4

P

= 400

Ibf/in.

2

(2.758

MN/m 2 )

C

40 e=

19_

einj= X/L=

6.5 0.5

ibf/in.

= 25 ° =

27.5 °

I

Triple

2

Fa =

H

Wa

1050

ibf (4671

orifice

Variable = 4.0

injection

N)

ibm/sec(1.81

do

kg/sec) -I 0 =

.01

0

.02

.03

tan I .04

Fs/F a .05

.06

I

I

;

i

0o

io





Figure 42. - Transformation of performance data for strontium perchlorate injectant (adptd. from ref. 108).

.07

Fs/Fa

I

e



2 (5.516

MNIm 2 )

Other some (figs.

useful LITVC

graphs design

37 through

are made to meet special design needs parameters on side specific impulse,

40).

The LITVC performance data accumulated represent motor configurations and operating motor and LITVC system being designed modification. The data is transformed from conditions

by applying

one

or more

For inert liquids been shown to

the momentum be the factor

impulse

changes

due

to

momentum principle shown in figure 40.

physical

in flowrate,

used

nozzle

this method is correlated residence

occupied

pressure,

to transform

the

laws that

data

available

appear

to be dominant.

energized

for injectant

or

density

through

(ref.

a change

total nozzle gas flow has changes in side specific 107).

An

in nozzle

example expansion

of the ratio

is

is the dominant effect. Accordingly, the most are based on the relative enthalpies and the fraction flow

for transforming data collected with a parameter representing time

The effects ratio have

by

from previous LITVC development programs conditions that are different from those of the and, therefore, cannot be applied without the original test conditions to the new design

of the injected flow relative to the that could be used to predict the

For reactive injectants, energy release successful data-transformation methods of the

and generally show the effect of force ratio, or thrust deflection

(refs. for one nozzle

mixing

and

143

through

146).

Figure

43 illustrates

reactive injectant. Side specific pressure and thermal energy

impulse and the

reacting.

of changes in nozzle geometry such as divergence angle, contour, and expansion been transformed by use of geometric, gas dynamic, and oblique shock wave

relationships. Some of the changes in nozzle geometry and can be transformed by simple geometric or vector summation

injection methods

geometry and spacing (ref. 107).

For changes in injector location or nozzle length, the coefficient of thrust relationship, separated into portions that are in or out of the injection region, can be used. The injection effect can then be assumed to change in proportion to the fraction of the motor thrust that originates in the injection region. This approach tends to favor injection at upstream locations in the nozzle, making it necessary to include a calculation of the degrading effect on the side force of the shock wave caused by injection when the shock wave reaches the other

side of the nozzle

(refs.

107,

126,

and

147).

A variety of computer programs for predicting the LITVC effect exist, but not one of them has adequately predicted the side force effect, because these programs are limited in the range of phenomena assumptions on which energy shock; reaction

addition; droplet with

thermochemistry,

that they they are

represent based are

displacement without breakup, vaporization, momentum interchange; and

shock

generation.

and the linearized

realism of supersonic

their results. Some of the flow with mass, bulk, or

mixing; boundary-layer separation and induced and bulk formation; mixing, vaporization, and and liquid breakup, mixing, vaporization, Use of these

113

computer

programs

has been

inhibited

2OO

E

O

150

!

J

O

,-4 O.

i00 O

J

U

v

Sr(Cl04) 5£ O 0J

2

Pinj

=



jet

injectant

1500

Ibf/in.

2 (10.342

deflection

MN/m

2)

angle

i

I00

200

(

300

Ps,inj

400

T3s,inj

d

5 00

)1/2

Vinj

Nozzle

parameters

Pc

Ps,inj

Ts,inj

ibf/in.2 einj

Symbol

O ® Z_

2

x

145)

(K

9/5)

ft/sec

(mx39.37)(m/sec

x

6.2

3.00

375

3010

2.66

8800

3.2

2.48

800

44.8

3550

1.83

7940

19

3.0

2.42

375

23.6

3620

3.74

7820

19

3.0

2.42

650

41.0

3620

3.74

7820

19

3.0

2.42

800

50.4

3620

3.74

7820

2. i

2.12

800

85.5

3980

2.57

7200

The

correlation

the

parameters

- Correlation (adptd.

of from

shown listed

injectant ref.

should

8.6

x

in.

j

7

Note:

43.

(MN/m

oR

Vin

19

7

Figure

Mini

d

be considered

in the above

specific

122).

114

valid

only

within

the

range

table.

impulse

with

key

nozzle

parameters

of

3.281)

by

lack

of

empirical

correlation

with

correlations

2.2.3.2

the

data.

for transforming

SMALL-SCALE

Early in information

test

Therefore, data

(ref.

the

general

practice

has

been

to

use

51).

TESTS

development on which to

period, the designer needs only approximate parametric define optimization studies and preliminary designs. Existing

LITVC data are employed as far as possible, transformation-correlating methods being used to transform the data to the current design problem. The transformed data are approximate at best and contain errors that are in proportion to the differences between the motors from which

the

data

came

and

the

motor

being

designed.

As the

design

proceeds,

better

data

are

needed; these data usually are obtained a variety of LITVC arrangements that

from tests of scale models of the motor nozzle with are in the range of design interest. There is little

scaling problem involved Figure 35 shows LITVC full-scale motor.

small-scale model from small-scale

in translating data obtained

A small-scale test series includes sufficient data for construction pertinent features

ranges of variation in the test conditions of the plots and correlations needed

design parameters (sec. 2.2.3.1). that represent its larger counterpart

injection

geometry,

2.2.3.3

and

FULL-SCALE

ambient

Also, the small-scale motor in propellant gas properties,

scaling

are

DEVELOPMENT

eliminated

high-confidence in the horizontal

data at the or vertical

and

possible

earliest position.

LITVC

time. The

tank

and

bladder,

quality

tubing,

insensitive and

design

Static tests orientation

is designed with nozzle geometry,

first opportunity, usually the first tests, errors of data transformation

changes

are detected

and

defined

by

are usually conducted with the motor of the motor is considered in selecting

for the

static

test

to allow

for the change

L ITY TESTS

The operating capability of the parts and determined at various stages of manufacture, relatively

that will provide to establish the

TESTS

the orientation of the LITVC tank and plumbing in direction of gravity force on the liquid.

2.2.3.40PERATING-CAPABI

a

pressures.

A full-scale test of a LITVC system is conducted at the static test of the full-scale rocket motor. In the full-scale and

data to a full-scale counterpart. tests compared with data from

fittings,

to malfunction

flow after

components assembly,

meters,

and

they

have

operability.

115

of the storage, check been

LITVC system are regularly and launch preparation. The

valves tested

have

been

to demonstrate

shown

to be

specified

The

most

critical

components

are

the

injector

valves

and

the

pressurization

system

because

they are sensitive to malfunction. Surveillance tests to monitor the operating capability of these components have been developed (ref. 46). The injectors are evaluated in bench tests with an inert liquid (e.g., Freon) that evaporates and leaves the components clean. While this evaluation is not fully representative of actual conditions, it is sufficient because it provides an

effective

functional

nonevaporating necessary. After on the

motor,

injectant assembly these

response through storage or launch When

test

of the

components

a gas generator

is used

for continuity

pressure checked

is monitored for electrical

A complete check rocket motor; this

and

without

degrading

is used in bench testing, thorough and installation of the injector valves are tested

the electric readiness.

voltage

components

feedback

to pressurize

resistance.

by actuating

loop.

These

the

injectant, of inert

by pressure gages. The squib continuity and resistance.

valve

the

igniter

at the

means

components after without activating

above,

it is possible

to

check

the system has been installed and it or disturbing its launch readiness.

116

the

the

function

charged

with

the

during

at low

is used,

the gas

of the inert-gas

of injector valves sometimes is conducted while check is accomplished by connecting an auxiliary

discussed

desired

is checked

pressure

outlet

or

testing is system

and checking

when

squib

at high

liquid into the LITVC system, actuating the injectors, and noting used is inert and evaporative to avoid contaminating the system. By the

valves

are repeated

gas

If a reactive

cleaning after and pressurization

the injector

tests

If a tank

them.

tank

is

the system is on the supply of pressurized response.

The

of all critical injectant

and

liquid

LITVC gas

but

3.

DESIGN

CRITERIA

and

Recommended 3.1

Practices

FLEXIBLE

JOINT

3.1.1

Configuration

3.1.1.1

DESIGN

OPTIMIZATION

The flexible joint design shall be based on the movable-nozzle constraints and joint, motor, vehicle, and mission design parameters either maximum performance or maximum cost effectiveness, depending The

basic

motor

rate, actuation environmental possible, designer.

on specific and

needs

vehicle

acceleration, conditions)

and characteristics

joint

design

of the program.

parameters

(motor

flight inertia loads, should form the basis

optimization analyses. The following procedure optimum joint design (i.e., the least expensive without violating any imposed restraints): Calculate reference

(2)

Prepare a anticipated parameters:

(3)

Vary

constraints, initial joint

anglel mass design.

actuation properties, Whenever

as explicit design points to the joint must be established on the basis of

is recommended joint that satisfies

for establishing the all mission objectives

against

for this motor should call for state-of-the-art materials, philosophy expected for the operational system, and be for all loading conditons. Calculate motor performance, and

which

the independent

weights

other design

for this

designs

independent

and

optimization parameters

parameters

analyses for use in the

117

motor

design.

will be compared

pivot point, and cone angleand nozzle design, motor performance, tradeoff

at some

preliminary layout drawing of a motor approximately the size for use in the vehicle. This motor is designed to a particular set of motor pressure, joint actuation torque, pivot-point location, and cone

performance,

design

vector

the required nozzle vector angle that will produce a side force position consistent with the vehicle performance requirements.

angle. The drawing embody the design structurally adequate joint

pressure,

envelope for the

the joint design parameters should be provided Otherwise, these interdependent design points

(1)

envelope that result in the choice

- motor

determine and cost to

motor

pressure,

is the

baseline

an optimum

design.

joint

actuation

torque,

their influence on joint design, if considered. Continue to perform

obtain

final

This to select

design.

the

near-optimum

values

of the

Since no parametric weight-scalingequationsare availablefor flexible joints, the basic joint design should be varied geometrically for pivot position, joint diameter, and cone angle; and the effect of these parameters on weight at different motor pressures and spring torques should be calculated. Conduct structural analyses,using the empirical relationships of section 2.1.5 to establish joint component thicknesses.Layout drawings of the nozzle andjoints should be prepared and compared with envelope constraints to establish limits for joint geometry as a function of pressureand spring torque. The joint weights as a function of motor pressure, spring torque, and geometric limits should be included in motor andvehicleoptimization computerprograms. (4) Make new layout drawings basedon the near-optimum values of the operating parameters and check to ensure that computer-predicted weights, lengths and volumes,and performancesarevalid. To ensurethe validity of the design,perform necessary calculations external to the generalized computer program; e.g., structural analysis(sec.2.1.5), detailed weight calculations,and grain design. Steps3 and 4 should be repeatedasnecessary.The joint designcharacteristicsresulting from this procedure must be consistent with the required motor characteristics and with near-optimum systemperformancewhen all stagesareconsidered. The dependent design parameters considered in sections 3.1.2.3 and 3.1.2.4, the independent design parametersconsidered in section 3.1.2.5, the material properties (sec. 3.1.3), and other important parametersincluding internal pressure,axial load on the joint, flight loads, and loads resulting from the particular motor or vehicle configuration (sec. 3.1.4) should be included in the optimization analysis to the extent required by the particular application. Specific recommendedpracticesfor componentcost analysiscannotbe madebecauseof the many complexities involved. Cost-estimatingtechniquespresentedin reference 148(ch. X) should be usedas a guide. The generalrecommendation for cost analysisis to establishthe joint design and then to continue to improve the design with cost effectivenessas the criterion. The mission performanceof the vehicle should be maintained constant for each design alternative evaluated.The analysismust include the cost of all motor components redesignedasrequiredto maintain constantvehicleperformance.

3.1.1.2

ENVELOPE

The

values

joint

can operate

It is recommended nor

greater

than

for

LIMITATIONS the

inner

and

outer

joint

angles

_1 and

{32 shall

so that

angle/3_

ensure

that

the

as required. that

the

45 °, and

flexible angle

joint

_2 is not

be designed less than

118

45 ° nor greater

than

is not

less than

55 °. (All

40 °

successful

joints to date have operatedbetweentheselimits, but joints with largervaluesfor/31 and t32 may be possible). To reduce consistent with the allowable compression

3.1.2 3.1.2.1

spring torque, the difference (/32 -t31) should stresses in the elastomer and reinforcements

requirements.

Design Requirements ACTUATION

TORQUE

The total actuation torque -consisting offset torque, inertial and gravitational be less than The

be a minimum and any axial

total

actuation

dependent contributing

on

the

torque

available

torque

is the

of foint torques,

from

spring torque, frictional and aerodynamic torques

torque, - shall

the actuator.

summation

of all the

contributing

torques,

each

of which

the specific design of both nozzle and motor. It is recommended that torque, including the variability of the torque constituents, be calculated

is

each for

the full range of motor service life. The service life consists of (1) vectoring for checkout at zero motor pressure and (2) vectoring over the entire range of motor operating pressures. Use the maximum actuation torques (nominal determine total required actuation torque, and actuation necessary

system. statistical

3.1.2.1.1

Joint Spring Torque

The ]oint

A valid statistical analysis data will not be available

spring

torque

shall

be the

plus maximum variability) thus obtained to compare this value with the capability of the

is not possible at this point of design, since until a joint is designed, built, and tested.

minimum

required

to fulfill

motor

the

operating

requirements. The joint spring material properties

torque should be calculated obtained in a subscale test

by the methods of program (sec. 3.1.7.1).

section 2.1.2.1.1; To establish the

use range

of probable variability in spring torque, calculate the joint spring stiffness at zero motor pressure for the maximum and minimum elastomer shear modulus. This range should be assumed to exist at all motor operating pressures. The

spring

actuator. control

torque

at the

maximum

The spring torque system. If the joint

value

of shear

at the minimum is to be vectored

modulus

is used

in the

design

of

the

value of shear modulus affects design of the to different angles during motor operation,

take advantage of the reduction in spring torque due to motor pressure to reduce the actuation power requirements. Calculations using the average elastomer shear modulus must be made of the joint spring torque during motor firing. The expected variability calculated at

zero

motor

pressure

must

be

superimposed

119

on

the

average

values

to

establish

the

maximum and minimum spring torques. It is desirablethat the minimum spring torque be sufficiently large to prevent a negative joint spring stiffness due to pressure.If a joint designedto be vectored at pressureis to be vectoredat zero pressureduring motor preflight checkout, the vector angle at checkout must not result in a joint spring torque greaterthan that occurring during motor operation. 3.1.2.1.2

Friction

The

joint

shall

stability Neither

Torque demonstrate

of the flight

the

coulomb

coulomb

control

friction

and

nor

the

viscous

design. Both frictions should be measured time of relatively constant motor pressure three

or

four

different

cycles at each actuator force actuation

rates.

viscous

friction

consistent

with

the

system.

The

wave

friction

can

be

estimated

during a static firing. be selected and that

form

should

for

preliminary

It is recommended that a the nozzle be actuated at

be sinusoidal

and

run

for

at least

IIA

rate to avoid the force transients that occur at the start and stop points. Plot variation with either vector angle or actuator stroke for one cycle at each

rate,

and

determine

the

average

actuator

force

at zero-degrees

vector

angle

(fig.

14(a)). The test data should be smoothed and the actual instantaneous actuation rate at zero-degrees vector angle determined either by calculation or by use of a plot of vector angle Variation with time. The variation of actuator force at zero vector angle with actuation rate should

be plotted;

friction

(fig.

3.1.2.1.3

record

the

zero

intercept

as the

friction

and

the

slope

as viscous

14(b)).

Offset Torque

The flexible-joint and movable-nozzle consistent with reasonable manufacturing A value

coulomb

for

determine

offset

torque

pressure

cannot

distributions

offset torque shall practice and cost.

be calculated around

the

unless

movable

be a minimum

air cold-flow nozzle.

For

tests joints

are

value

conducted

to

up to 22 in. (55.88

cm), the offset torque is small compared with the joint spring torque, and it is recommended that it be ignored in estimating actuation torque. For larger joints, an assessment should be made of the offset torque, pivot-point movement (sec. 2.1.2.3) being considered

and

measured at

worst-on-worst

during

a minimum

requirements, 3.1.2.1.4

by and

Inertial

The actuator the

the

moving

bench

tolerances test

maintaining motor

being

program.

assumed.

The

It is recommended

minimum

tolerances

offset that

consistent

torque

should

also

the offset

torque

be kept

with

design

due

to the

practice,

cost

requirements.

Torque torque

shall

provide

for

the

nozzle.

120

maximum

torque

inertia

be

of

The inertial torque should be estimatedfrom the massof the movablenozzle assumedto be rotating about the geometric pivot point. It is recommendedthat half of the weight of the flexible joint be included with the movable section in calculating movable nozzle weight, center of gravity, and dynamic moment of inertia. It is recommendedthat the maximum inertial torque be included in the actuation torque. 3.1.2.1.5

Gravitational

The actuator accelerations. Calculate

the

Torque

torque

axial

and

shall

lateral

provide

accelerations

vehicle pitch accelerations

and yaw. The torques should be calculated

recommended

that

3.1.2.1.6

the

maximum

Insulating-Boot

for

the

at the

acting in the

gravitational

maximum

nozzle

insulating

modulus of requirements.

boot

torque

must

be

fabricated

insulating boot must be the bellows used, a wrap-around insulating boot that

even

It is difficult

to estimate

due

to

of gravity

that

pivot point for inertial

be included

in the

vehicle

result

from

due to torque.

actuation

these It is

torque.

Torque

such

elasticity and thickness) and If a material such as silica-filled

recommended allows.

center

at the geometric same manner as

The insulating-boot torque shall be a minimum requirements and available motor envelope. The

torque

with

the

this

that

consistent

it has

with

the

a minimum

stiffness

yet is thick enough butadiene acrylonitrile

to

a bellows-type

insulating-boot

diameter, with a bellows fabricated recommended that the insulating-boot

of

torque.

boot

For joints

be used

up

(product

of

satisfy insulation rubber is used, the

type, whereas if a silicone rubber such (fig. 7) will result in low boot torques.

material

insulating

when

as DC 1255 is However, it is the envelope

to 30 in. (76.2

silica-filled butadiene acrylonitrile torque be assumed to be 35 percent

cm)

in

rubber, it is of the joint

spring torque. With the same insulating-boot material for joints approximately 90 in. (2.29 m) in diameter, it is recommended that the insulating-boot torque be assumed to be 15 percent of the joint spring torque. For designs using low modulus silicone rubber, it is recommended spring torque. 3.1.2.1.7

Internal

A ctuator The and

that

aerodynamic propellant

the

insulating-boot

Aerodynamic

torque

shall

include

torque

be

assumed

to be

25

percent

of the joint

Torque the effects

of internal

aerodynamic

torque.

torque must be estimated as a function of vector angle, motor pressure, grain/nozzle configuration for the maximum expected vector angles during

121

motor operation. The torque should be determined from a knowledge of the pressure distribution along the nozzlesurfaces,using the methods outlined in section2.1.2.1.2 (i.e., air cold-flow testsor two-dimensionalmethod of characteristics). When a joint has a forward pivot point, the total aerodynamictorque must be addedto the actuation torque, so that the actuator can be sized properly. When a joint has an aft pivot point, the aerodynamictorque should be ignored.

3.1.2.1.8 The

External

Aerodynamic

Torque

external

aerodynamic

torque

during For

in which

the

nozzle

cause

a negative

is not

shrouded

by

a motor

torque in the high dynamic pressure region that This torque should be determined from a knowledge

along the nozzle external surfaces internal aerodynamic torque. The pressure

region

3.1.2.2

NOZZLE

The

not

actuation

torque

flight.

all motors

aerodynamic estimated.

shall

must

be less than

VECTOR

vector

angle

and total

the joint

ANGLE

shall

should be aerodynamic

be

large

spring

AND

PIVOT

enough

skirt,

the

external

occurs during flight must be of the pressure distribution

calculated torque

stiffness

case

in the stiffness

to ensure

same manner as the in the high dynamic

positive

actuation.

POINT

to cause

sufficient

side force

for

vehicle

steering. The vector angle required for steering either must be given in the motor requirements or calculated from a trajectory analysis that considers pitching requirements and worst-case winds. A method for calculating the required vector angle is given in reference 149. If

the

vector

angle

is given

in the

motor

(normal distance from the line of action vehicle center of gravity) or the required It is assumed that the side force causing point,

and

the

effective

pivot

point

requirements,

the

control-force

moment

arm

of the motor thrust for a vectored nozzle to the steering moment must be stated as a requirement. a steering moment acts through the effective pivot

should

be calculated;

from

this location,

the geometric

pivot point should be determined. The geometric pivot point should be as far aft as possible consistent with optimum vehicle performance. However, envelope restrictions on actuators and exit cone movement must be considered. It is recommended that a forward pivot point be

used

submerged

for

nozzles

nozzles

with because

little the

or exit

no cone

submergence, movement

122

and requires

an aft

pivot

less envelope.

point

be used

for

3.1.2.3

AXIAL

DEFLECTION

Clearances effects Joint

axial

between

the

movable

and fixed

nozzle

components

shall allow for

of axial deflection. deflection

is the

compressive

response

of the

flexible

joint

motor is pressurized. The clearances between the movable and must be sized to allow for this movement as well as for rotational The required clearances the nozzle as it deflects The

axial

considers

should be studied through axially and in the vectored

deflection the

should

geometric

be calculated

changes

loading. As soon as possible axial-deflection characteristics spring

stiffness

3.1.2.3.1 The

must

nozzle

caused motor

be known

Misalignment

nozzle

shall

have

must

be

by motor pressure.

assembled

pressure

Efforts occurs

should be made during in a nozzle, since the

excessive follows:

during

which

misalignment

(1)

Estimate effective

(2)

Estimate

layouts

overlaid

analysis

(sec.

in at least

joint

that

the

the

to show

2.1.2.3)

four

of the guidance

control

that

increments

of

at zero

system.

pressure

that

in the

motor

at some

vector

angle

length actuators will result that the pressure at which

results

in

vectoring

such

the

vectoring

that

in alignment alignment

at a selected occurs be the

occurs.

the joint design to estimate the amount of misalignment that orientation of the actuator to the nozzle could result in A recommended

procedure

for estimating

misalignment

the axial compression of the joint (sec. 2.1.2.3) and pivot point (sec. 2.1.2.3.1) during motor pressurization. the

when

pressure.

nozzle

angles.

occurs

should be bench tested to measure the compressive spring stiffness. The axial

misalignment

pressure and fixed It is recommended

average

loading

that

fixed nozzle components movement of the nozzle.

of two

a finite-element during

for the design

motor

the use position.

program, a joint obtain the axial

a vectoring

at a selected

with

of the joint

in the and

Nozzle

alignment The

the

spring

torque

stiffness

(sec.

the

is as

approximate

2.1.2.1.1)

during

motor

determine

graphically

pressurization. (3)

Assuming nozzle operating

(4)

Assume

vectoring

nozzle

is aligned

misalignment

as the

at zero motor

pressure, is pressurized

to maximum

the

expected

pressure. that

the

nozzle

as the misalignment calculate the actuator

misalignment

that occurs null length.

required

at the

123

selected

at zero motor

pressure

zero-misalignment

is the

same

pressure,

and

The actuator null length must be checked during the static firing test program. The recommendedprocedureto determinethe actuator null length is asfollows: (1) Estimate the effective pivot point at the motor pressureat which the nozzle and motor center lines are to be aligned (sec.2.1.2.3). (2) Align the nozzle to the motor at the pressurefrom item (1), and calculate the vector angleand actuator length at zero motor pressure,consideringthat the pivot point movesfrom the effective pivot to the geometricpivot point. (3) Prior to the firing, actuatethe nozzle in the motor and determine :

per inch

of actuator

the vector

angle

stroke.

For the static firing, set the actuator length as determined in item (2) and measure the vector angle change of the nozzle at various motor pressures during the firing,

(4)

the pressures being selected held at the trial length from (5)

Compare

the

pre-firing

to give as wide a range as possible item (2) for at least one half-second.

and

firing

data

to calculate

the

at its natural

frequency

with

amount

the

actuators

of zero-pressure

misalignment.

3.1.2.4

FREQUENCY

The

nozzle

RESPONSE

shall

not

be subject

to excitation

The stiffnesses

of all parts

of the nozzle

are higher

the

frequency

than

natural

should

of the

be designed

hydraulic

so that

actuator

frequency is almost equal to the natural frequency of the nozzle and the actuator system will occur and will produce frequency is less than the system will occur. Further, mechanical destructive The

natural frequency the nozzle natural

frequencies of the motor and vehicle failure of the nozzle results.

natural

firing. The consideration

frequency

of the

nozzle

assembly should be of the control system

and

motor

subjected response,

assembly

their

system.

natural If the

frequencies nozzle

that

should

to a frequency but if this is not

is known, a notch filter should be incorporated vectoring commands at or near the natural frequency.

124

of the natural

coupling with the guidance be greater than the natural no coupling

that

be measured range known,

into

the

could

prior

cause

to static

determined from it is recommended

that a frequency range from 2 to 100 Hz be tested. If the motor is too large frequency response tests, the natural frequency must be calculated. When frequency suppress

natural

actuator system, coupling instability. If the nozzle

of the actuator, frequency must to ensure

of vibration.

control

for practical the natural system

to

3,1.2.5

ENVIRONMENTAL

3,1,2.5.1

Thermal

Thermal

PROTECTION

Protection

protection

temperature

of

limits

the

for

joint

the full

shall

enable

duration

it to remain

motor

gases

be sufficiently motor shade

and

maintain

thin

the

to minimize

joint the

vectoring. For region in order

that reduce the the fixed nozzle

the radiation to minimize

additional stagnant

The

temperature.

torque

An

component

that a radiation gas. This practice

boot torque. Provide component to allow

protectors a result of

(fig. 7(b)) vectoring

insulating

due shield allows

to the

motor

gas as the joint

boot boot.

a clearance gap between for joint axial deflection

the and

must be located in a stagnant gas as the joint is vectored. must be or motor

sufficient pressure;

to prevent otherwise,

be located in a circumferential

is vectored.

Aging Protection joint

elastomeric

oxidation

during

Polymerization conditions that determined

material

shall

pre-fabrication

of uncured maintain

early

shear specimens properties. (2)

not

be subject

to adverse

and post-fabrication

(sec. 2.1.7.1) Store uncured

by

the

following

steps:

from new elastomer elastomer at different

of aging and

storage.

elastomer should be minimized by the elastomer within specifications.

in a program

effects

storing These

(1) Fabricate stock to conditions

the elastomer under conditions must be and

establish for the

test quadruple-lap initial elastomer time period it is

anticipated the elastomer will be stored during the program. (3) Fabricate quadruple-lap shear specimens from the stored elastomer stock to establish the elastomer properties. (4) Select storage conditions to be included in the processing To

must If the

(fig. 7(a)) be used to use of thinner, more

torque is generated. It is recommended that the joint protectors region in order to reduce the size of the protectors and to minimize

of the

3.1.2.5.2

ablative protectors (fig. 7). The the erosion by the flow of the

shield to be effective, the gap circumferential flow of the motor

The gap between sacrificial thermal contact of adjacent protectors as

flow

at allowable

additional

envelope allows space, it is recommended the insulation boot from the hot motor

pliant boot materials radiation shield and

allowable

of the firing.

Protect the joint with an insulating boot or with sacrificial insulation material must be sufficiently thick to withstand hot

at or below

minimize

and test change in elastomer

specifications. changes

in joint

performance,

select

elastomeric

materials

for which

long-term

aging data are available. To protect the joint against changes in the elastomer properties surfaces exposed to ozone or oxygen, it is recommended that the joint be covered by impervious

coating

such

as chlorobutyl

rubber

125

or Hypalon.

at an

3.1.2.6

PRESSURE

The 'joint

SEALING

shall

pressure

and

not

leak

vectoring

It is recommended

that

when

subjected

to either

a pressure

load

or a combined

load.

reliable

joint

sealing

be

accomplished

by

joint molding process until unbonded areas are at a minimum to ensure that this process is continued on all subsequent should be performed to bonding of the elastomer, after joint molding by

experimenting

determine unbonded areas. For joints fabricated inspect the elastomeric pads before joint molding C-scan ultrasonic techniques (ref. 22). Joints

by secondary and the bonds fabricated by

only by cutting joints fabricated

processes

the

inspected

on

a sampling

basis

to

ensure

debonded

area

have

not

the

and then establishing controls manufacture. An inspection

compression molding and injection molding can be inspected and inspecting the elastomer surface. It is recommended that be

with

that

molding

apart a joint by molding

process

has

not

changed. Quantitative

criteria

for

that the photographs an acceptable joint, two examples

of unacceptable

Material

3.1.3.1

ELASTOMERS

for structural rate, and joint

shear

rate

properties

problem minimum

It is recommended shows shows

joints.

material

The important mechanical are secant shear modulus reinforcements shear strain

established.

Selection

elastomeric

needed actuation

been

presented in figures 44 and 45 be used as a guide. Figure 44(a) figure 44(b) shows a marginally acceptable joint, and figure 45

3.1.3

The

the

loading at temperature,

rate,

and

maximum

joint

loading

the minimum

the critical as imposed

in a quadruple-lap temperature (sec.

be determined

(ref. 78 and sec. values for these

actuation

at least

mechanical

motor pressure, by design factors

properties

vector angle, of safety.

properties to consider in the selection of the elastomeric material at 50 psi (0.345 MN/m 2 ), shear strength, and bonding to the metal

- all measured and operating should

shall possess

joint

2.1.2.1.1). mechanical temperature

as evaluated

if joint

shear specimen tested at the appropriate 2.1.7.1). The effect of compression on the

instability

due

to motor

pressure

is a potential

The materials should be selected on the basis that the properties at the critical motor pressure, vector angle, are

not

by appropriate

less

than structural

those

required

analyses

(sec.

to withstand 2.1.5).

The specific material mechanical properties should be established from pre-existing on the selected elastomer material, or these properties should be established from

126

the

test data specimen

t"--

_4 er 0

¢O r_

E o m

0

2_

¢,a

2_

E X

o |

u5 L_ 2_ °_ t,I.

128

tests (sec. 2.1.7.1). section 2.1.3.1.

3.1.3.2

Materials

that

have

been

used

in successful

joint

programs

are given

in

REINFORCEMENTS

The

reinforcement

properties angle,

material

needed

for

as imposed

The important are the modulus

shall

structural

by design

possess

loading

factors

at

at the

least

the

critical

minimum

motor

mechanical

pressure

and vector

of safety.

mechanical properties to consider in the reinforcement material to be used of elasticity, the compressive yield strength, the ultimate tensile strength,

and, for composite reinforcments, the interlaminar shear strength. For joints with metal reinforcements, the required buckling stress of the reinforcement can be calculated (see. 2.1.5.2) from the modulus of elasticity and joint dimensions. For joints with composite reinforcements, the allowable compressive MN/m 2 ). The true allowable compressive from bench testing a joint to failure (sec. basis

that

the

minimum

values

and vector angle are not evaluated by appropriate The specific representative

material mechanical of the selected

evaluation of reinforcements. composite

3.1.3.3 The

specimen Aluminum

tests. alloys

reinforcements

ADHESIVE adhesive

that

the

mechanical

be assumed to be 60 000 psi (414 laminate used must be determined materials should be selected on the

properties

at the

those required to withstand analyses (sec. 2.1.5). properties material, Steel should

critical

the maximum

should be established or these properties

motor joint

pressure loading

as

from existing data that should be established

are by

or composite materials are recommended as also be considered for reinforcements but only if

are impractical.

BOND bond

properties needed angle; as imposed To ensure

for the

less than structural

stress should stress for the 2.1.4.1). The

SYSTEM system

shall

possess

at

for structural loading at the by design factors of safety.

adhesive

bond

system

is stronger

least

the

critical

than

minimum

motor

the

mechanical

pressure

elast0mer

and vector

material,

all failures

in a specimen test program (sec. 2.1.7.1) must be cohesive. The processing of the specimen must be as nearly identical to that of the joint as possible. To maintain the quality of the adhesive bond system, controls on the system materials must be established. Systems recommended for use with injection-molded joints, compression-molded joints, and secondary-bonded

joints

are described

in section

129

2.1.3.3.

3.1.3.4

JOINT

The

The

THERMALPROTECTION thermal-protection

materials

properties

joint

needed

to maintain

joint

important

thermal

properties

diffusivity, flexibility have been

shall possess

temperatures

for the joint

at least the minimum

at or below

thermal-protection

thermal

allowable

limits.

materials

are low thermal

high heat of ablation at strain levels anticipated in service, and mechanical with minimum char fracture at temperatures expected in service. Materials that used in previous programs are recommended; these are presented in section

2.1.3.4.

3.1.4

Mechanical

3.1.4.1

GENERAL

Design

CONSIDERATIONS

The flexible joint shall possess the combination of weight and structural that contributes most to optimum motor and vehicle performance. The

flexible

joint

subjected to accompanying integrity section

the

should 3.1.5.

should

be

designed

to

have

the

required

structural

critical design loads of motor pressure and vectoring environmental conditions. Analytical verification of be made;

the

recommended

practices

for

structural

strength

capability and the the joint analysis

while

effects of structural are given

in

If axial compressive deflection is a requirement that cannot be met by a joint sufficient for structural strength, the thickness of the elastomer layers should be reduced, the result being an increased number of elastomer layers. The number of reinforcements will be increased, and these in section

should be designed 3.1.5.2. Compliance

demonstrated Because the the amount limiters storage

for structural capability according to practices recommended with the axial compressive deflection requirement must be

by test. joint has little axial stiffness in tension, the design .must incorporate limiters oia of tensile axial deflection that can occur as a ,result o;f ground handling. The

must

also

ensure

that

the

cannot

over-vector

the

joint

during

horizontal

or transportation.

The joint design should be established close to zero as possible. However, the

nozzle

guidance

less-than-optimum

control joint

system design

and

to obtain positive margins of safety since the joint design is interdependent optimum

will result

motor

in optimum

130

performance, motor

design.

it

(sec. 2.1.4.1.1) with design is

possible

as of that

3.1.4.2

DESIGN

The joint specified

FACTOR

shall

have

joint

OF SAFETY at least

the

minimum

factor

of safety

required

A design factor of safety should contingencies (e.g., approximation

be used in the design in estimation of joint

of

loading

developed variables

through involved.

(i.e.,

operational

or

handling);

these

that

define

elastomer

ring thickness,

The

reliability

the

the

joint

structural

and joint

cannot

tests and joints involved. convergence of the curves upon

number

capability

geometric

be demonstrated

failures

The not

upper

After each probabifity

and lower

3.1,4.3

have

understanding of the is not available, it is

design factor

than is applied to of safety is 1.25,

factor should be applied be applied redundantly

(e.g.,

material

been

mechanical

to the to the

properties,

explicitly

because

that the reliability

allowed

during

of the

prohibitive

number

reliability be demonstrated levels. The upper reliability the

development

and

reliability

levels

should

be set up before

of

by the level is

production

the lower reliability level is based the development and production

test, the reliability from all test results is plotted and extrapolated of achieving the required reliability. A test program to establish

FLEXIBLE-JOINT

The joint combination

safety

tolerances).

It is recommended for upper and lower of

joint. must

programs and must be greater than the required reliability; upon the calculated reliability from test results during programs. show the

of

a history of successful designs and a knowledge and Since in the design of flexible joints this history

then a factor of 1.5 should be applied to the motor pressure and to the vector angle. It

based

factor of safety could to joint performance

factors

recommended that a greater factor of safety be applied to the joint the overall motor design. For example, if the overall motor design

joint

for in

the required reliability (ref. 150). Unfortunately, there is insufficient of how these variables affect joint performance, and a single factor of safety Usually design factors of safety are specified in a design for specific classes

conditions

parameters

the

of flexible joints to account stresses, undetected variations

material properties, and undetected manufacturing deviations). The be established from a statistical study of all variables contributing correlated to understanding is recommended.

to obtain

reliability.

development

program

to the

is begun.

LOADS

stress profile shall of design loads.

include

all

individual

design

loads

or

the

worst

All design loads (see. 2.1.4.1) should be used to determine the critical design stresses. The critical joint loading condition, or worst critical combination loading, should be defined by summation of a load/time history of the joint. This profile should be prepared by tabulating all design loads, temperature exposure, critical-loading condition for each structural

and vectoring conditions element of the joint should

131

encountered. The be used in the joint

structural analysis(sec.3.1.5) than

3.1.5

Structural The joint

The

theories

should

that

margins

of safety

for the joint

are not less

be

design

Analysis stresses

necessary analyzed

preliminary and 82). The

to determine

zero.

to with

dimensions

following •

factors

Loads

shall not analyze the

and

of

joint

empirical with

be included

should

the allowable

a flexible

reanalyzed

should

used

use

exceed

stresses.

have

not

relationships

nonlinear

loads

(i.e.,

formulated.

(refs.

17

finite-element

in the requirements

be design

been

loads

79)

methods

for the

limit

and

The

structural

times

joint

to obtain

(refs.

80, 81,

analysis:

appropriate

factor

of

safety). •

Combined

loading

should

be analyzed

The maximum permissible minimum 3-standard-deviation quadruple-lap shear strain The

maximum

limited ultimate •

The loads

shear rate.

maximum should

specimen

permissible

to the loads.

shear

0.2 percent

permissible be the lesser

to determine

the resultant

stress in the elastomer should values of the failure shear stress

(sec.

2.1.7.1)

at the

tensile

stresses

in metal

yield

stress

compressive

appropriate

at limit

loads

stress

in metal

of the 0.2 percent

yield

ELASTOMER

The

elastomer

adequate The shear calculated

shear

THICKNESS thickness

shall

be limited measured

to the

and

and

should

ultimate

reinforcements

stress

to the from a

temperature

reinforcements and

be

stress

at

at ultimate

the buckling

The maximum permissible stresses in composite reinforcements assumed to be 60 000 psi (414 MN/m 2 ) and must subsequently the reinforcement laminate in bench tests to failure.

3.1.5.1

stresses.

stress.

should initially be determined

be for

..... not

be

greater

than

the

thickness

that

provides

strength.

stress in the elastomer at ultimate conditions.

due to combined motor The empirical method

132

pressure and and procedure

vectoring must be given in section

2.1.5.1 are recommended.When calculating the shearstressdue to vectoring,allow for the reduction in joint springtorque due to motor pressure(sec.2.1.2.1.1). Although the allowable shear stress at failure is increased when compression is superimposed,ignore this increasewhen establishingallowableshearstresses.

3.1.5.2

REINFORCEMENT

The

reinforcement

adequate :

The '

THICKNESS

and

procedure stress due

shall

hoop

and buckling

compressive

compressive

pressure

thickness

stress

vectoring

on

the

must

inner

be

2.1.2.1.1).

The

allowable

compressive

stress

,

from

bench

tests

of the

at ultimate

of joints

ADVANCED

The

The

design

analyzed t methods.

finite-element

method

thickness, thickness,

provide that

by

loads

to combined empirical

When calculating spring torque due

for metal

motor

method

and

the compressive to motor pressure

reinforcements

tensile stresses and fracture

methods

of analysis

must

be the

shall

involve

description be divided

should

be the

as shown must

in be

are important. The allowable mechanics properties of the

be

confirmed

be divided into and reinforcements that the analysis 2.1.5.3 be used.

average

calculated

a sufficiently

by

a minimum be divided

include

stress

133

refined

of the internal into a minimum

stresses for combined motor pressure stresses as described in sections 3.1.5.1 should

The

nonlinear



each reinforcement and both elastomer

The calculated the allowable

due

conditions.

to failure.

empirical

an accurate each elastomer

layers. It is recommended methods outlined in section

comparison

reinforcement

ANALYSIS

finite-elemen

panels to recommended

provides

and the buckling stress calculated stress for composite reinforcements

If a joint is to be used a number of times, the tensile stresses must be based on the fatigue reinforcement material.

3.1.5.3

that

:

at ultimate

lesser of the 0.2 percent compressive stress section 2.1.5.2. The allowable compressive

thickness

strength.

surface

be calculated

minimum

given in section 2.1.5.2 are recommended. to vectoring, allow for the reduction in joint

(sec.

determined

the

various

of nodes

and

stress distribution. It is of four layers across the of into

three layers across the a minimum of t 2 radial

nonlinear

and vectoring and 3.1.5.2. at the

grid

centroid

effects

and

that

the

should be compared with The applied stresses in this of each

panel.

3.1.6

Manufacture The

joint

joint

fabrication

and program

process

shall

be the

most

cost

effective

for

the

particular

needs.

An engineering study of fabrication fabrication processes that afford the costs. The engineering study should

processes should be accomplished best compromise between fabrication include detailed tradeoff evaluations

to select the schedule and of fabrication

methods;

reliability

status

past

program: fabrication, The

behavior

included

experience

research, tooling, of the

material

as a tradeoff

3.1.6.1

with

development, and facility

and

the

various

processes;

when

parameter

it is exposed

when

to various

alternative

fabrication

structural

materials

reinforcement

particular Metal

joint

reinforcements

fabrication

processes

limiting axial recommended recommended the material required

should

be

are evaluated.

are

either

compression for research

prior

reinforcements

shall

be

those

most

suitable

heat

treated

treatment

considered

thin

or thick,

requirement or small

the

difference

having

the

an influence

(sec. 2.1.4.1). Hydroformed development programs. Spun

programs. condition,

to final

should

be

to the required will cause

in the

for

assembly

on

the

Thin reinforcements are defined as reinforcements that can or spinning (sec. 2.1.6.1) and will be used in joints with a

for production in a normalized

properties

processes

reinforcements reinforcements

some of

are are

For both types, the forming should be made with and the material should be heat treated to the

machining. machined

from

plates

for

research

or small

programs. The plate should be normalized for rough machining and heat required properties prior to final machining. For production programs, thick should be stamped to the required shape with the material in the normalized

Heat

the and

needs.

possible method of fabrication. be fabricated by hydroforming

then

of

on schedules;

REINFORCEMENTS

The

Thick

of

or production; effect of the processing costs versus the joint configuration.

properties

prior

distortion

of the

a joint

by

spots and then assembling the reinforcements elastomer thickness will be circumferentially Although composite reinforcements have and molding, and molding with a mixture

to final

so that uniform.

the

treated to the reinforcements condition, and

machining.

reinforcements.

inspecting

development

This

reinforcements

all the

high

spots

distortion for high

should and

are aligned

be low

and the "

been fabricated by winding and molding, lay-up of chopped fiber and resin, it is recommended for

134

all production programs that composite reinforcements be fabricated by laying resin impregnated cloth cut into specific patterns into a matchedmetal mold and curing under pressure at a temperature and time suitable for the resin. However, in research or development programs, consideration should be given to compression molding with a compound of choppedfiber andresin.The sacrificial ablativeprotector (sec.2.1.3.4) should be fabricated asan integral part of the reinforcement.

3.1.6.2

JOINT

The joint The

joint

ADHESIVE adhesive

adhesive

SYSTEM

system

shall

system

not fail before

must

be

the elastomer

evaluated

prior

to

material. joint

fabrication

by

use

of

quadruple-lap shear specimens (sec. 2.1.7.1); an acceptable system must fail cohesively. The specimens must duplicate the thickness and cure condition of the elastomer and bond system in the joint. Fabricated joints should be bench tested at least to ultimate pressure and vectoring conditions to demonstrate the structural capability of the adhesive bond system. Failures

can

thickness,

the

occur

when

viscosity

the

bond

of the

sprayed on the reinforcements, these items should be included Each

lot of adhesive

and quadruple-lap variation.

3.1.6.3

FLEXIBLE

The joint

system shear

is either

and the

too

adhesive,

thick

the

or too

rate

materials to

should

ensure

be tested

quality

and

prior to

thin.

at which

and the time for spraying should in the joint fabrication specification.

tests

to use

maintain

To

these

control

the

materials

are

be monitored;

limits

in a joint

by peel

a record

of

on

tests

lot-to-lot

JOINT

fabrication

of the particular

system

primer

process

shall be consistent

with

the needs

and

characteristics

joint.

The molding process selected must depend primarily upon the number of elastomer layers, and the thickness of the elastomer rather than on the scope of the joint program. Joints with thin

dimensions of the joint, the layers and reinforcements elastomer layers (layers that

cannot be fabricated by injection molding) should order to improve the bond to the reinforcements.

by compression molding in molding has been successful

on joints up to 60 in. method is recommended programs. molding

Injection method.

be fabricated Compression

(1.52 m) in diameter with thick and thin reinforcements, and this for research and development programs as well as for production

molding Secondary

is a proven production bonding is a proven

135

technique process

and should be evaluated and should be evaluated

as a as a

molding method, particularly for large joints where significant cost savingshave been indicated. Prior

to

molding

process molding,

the

injection

on elastomer thickness the first development

This practice done by the Advantages

3.1.7

by

and joints

allows examination injection process, and disadvantages

or

compression porosity should

processes,

the

effect

should be evaluated be cut open to show

of

the

(sec. 2.1.6.3). After the joint cross section.

of the elastomer layer thicknesses, and if molding determination of the effectiveness of the elastomer of the joint

fabrication

processes

molding

are listed

in table

has been injection. VIII.

Testing

3.1.7.1

SUBSCALE

The

subscale

mechanical

TEST

PROGRAM

specimen

test

properties

The important mechanical failure, and the strength QLS specimens should in the joint. The bond QLS specimen Joints

should

have

been

used

program

shall

provide

values

for

the

elastomer

in design.

properties of the bond

for the elastomer are the shear between the elastomer and the

modulus, shear stress at reinforcement material.

be tested at the strain rate and over the temperature range expected between the elastomer and reinforcement should be cohesive, and the be used

to develop

designed

and

a satisfactory

tested

adhesive

successfully

and bonding

without

including

system. the

effects

superimposed compression and shear. However, if a joint is to be designed to operate pressure to take advantage of the reduction in spring torque due to pressure, the change shear modulus due to pressure must be measured. The reduced shear modulus is used predict spring torque 2.1.2.1.1). A method reference 78. If aging data are not be initiated as soon

and that

the has

of at in to

motor pressure at which the spring torque is unstable (sec. been used to measure the changed shear modulus is given in

available, a subscale test program to evaluate aging as possible in the motor program. This program

aging characteristics life and (2) several

of (1) several lots of the cured lots of the uncured elastomer

storage months

cured elastomer, the recommended test intervals are monthly up to six thereafter. For the uncured elastomer, the recommended test intervals

life. and

For the annually

are weekly

until

A subscale

test

and to establish

the shelf program acceptance

life has been should

be used

elastomer in order

characteristics must should evaluate the

to enable prediction to define uncured

of service elastomer

established. to evaluate

criteria.

136

lot-to-lot

variation

of elastomer

material

3.1.7.2

BENCH

Bench

TEST

tests

production the nozzle A joint establish The

of

]oint

characteristics

joints and shall verify clearance envelope.

bench axial

test

PROGRAM

that the

test program must be deflection characteristics,

for

compressive

axial

shall

establish

effective

acceptance

pivot

point

set up during the motor vectoring characteristics,

deflection

should

be

freely

about

to conducting measure the null

its effective

the vectoring actuator force

position.

The

pivot

point

while

tests, a pressure test and hence the offset

in a test

vectoring

tests

should

fixture

with

an

pressure and associated that allows the joint to

as it would

should torque

with

development program to and joint pressure sealing.

conducted

oriented

for

is compatible

unloading piston (fig. 21) so that the joint is subjected to the motor axial load. The vectoring test should be conducted in a test fixture rotate

criteria

be in the

motor.

Prior

be conducted in the same fixture to necessary to maintain the joint in a

be conducted

with

and

without

the

joint

ihermal

protection to determine the effect of the protection on actuation torque. In addition to axial deflection, vector angle, and actuator force, the hoop strain on the inner surface of each reinforcement should be measured. To ensure that only reliable joints are used in a motor, a stringent be conducted after The

same

criteria

tests

for

should

the

tensile-pressure leak the axial compression

should

be

joints.

If

be removed,

It is necessary should

that

be made

operating follows:

(l)

the

position

fails

target

light,

motor

acceptance used

effective

average

recommended

the

test

program

in the

should

as acceptance

elastomer,

the

elastomer

again. pivot

motor

production

this test

be determined

operating

procedure

to

pressure, find

the

for each

joint.

and maximum effective

pivot

A test

expected point

is as

target on a part of the test arrangement that is rigidly end ring and is near the theoretical pivot point. The

leg is to be aligned

coincident

with

the

center

line

of the

fixed

joint

ring.

Pressurize the

an

of the

pressure,

The

during

reinforcements

Mount a cross-hair-shaped connected to the movable end

(3)

a joint

the

pressure.

axial

(2)

conducted

and

at zero

test (sec. 2.1.7.2) is recommended; and vectoring tests.

nozzle and

Interpret

the

test

arrangement

vectoring open the

and

actuate

requirement.

the Camera photograph

shutter

the joint

Illuminate for one

as indicated

to an angle

the

cross-hair

complete

actuation

in the

sketch

in figure

at least

target

with

as large

as

a strobe

cycie. 46 to find

the

pivot

point. It is recommended between fixed and

that acceptable movable nozzle

limits on pivot-point components, rather

137

location be based than on clearances

on the tailored

clearances to fit the

Reference

line

+ Effective

pivot

point _ Axial point

pivot-

coordinate Reference

Figure 46. - Sketch

illustrating

determination

factors

of effective

138

involved pivot

in experimental

point.

line

measured pivot point. The clearance past with the purpose of providing radiation then should be established to be compatible The

recommended

set of layouts

design

practice

of the nozzle.

The

the radiation shield should be fixed in accordance protection, and the pivot-point acceptance limits with the required clearances.

to study movable

the effect

of pivot-point

components

are drawn

location on one

is to prepare

sheet

and

a

the fixed

components on another sheet. Superimpose the two sheets with an axial deflection appropriate to the pressure being considered, and successively pin the two sheets together at a series of pivot points. The limiting pivot point should be one that just permits the movable component

3.1.7.3

to rotate

to the

STATIC-FIRING

The

static-firing

requirements interact with Measurements misalignment coefficient develop

nozzle

program

shall demonstrate

and shall provide the nozzle. be

made

requirements, the nozzle,

a statistical

vector

angle.

PROGRAM

should of

required

that

the

data

needed

during

the

static

the joint

design

to design

firing

other

fulfills

the motor

components

program

to

that

determine

friction characteristics, natural frequency, and axial deflection, and vectoring capability. Sufficient

variation

should

be

obtained.

requirements. The final design of the guidance the results of the static firing tests.

control

Compare

measured

system

should

results

nozzle damping data to and

motor

be in accordance

with

The actuation power requirements should be established during the static firing. Certain increments to the actuation torque-friction and insulating-boot torque--cannot be calculated. With a bellows-type design (fig. 7(a)), the boot torque has been as much as 50 percent of the spring torque for joints up to 30 in. (76.2 cm) diameter (ref. 13). Therefore, when a bellows-type insulating boot is exposed to the motor environment, it is recommended that the actuator be capable of developing 50 percent more torque than the sum of the calculated increments to the actuation torque (sec. 2.1.2.1). When an exposed wrap-around insulating boot is used with joints up to 30 in. (76.2 cm) diameter, the actuator should be capable of developing 75 percent more torque than calculated. For an insulating boot protected by a radiation shield (fig. 7(a)), the insulating material usually is a soft silicone rubber (e.g., DC 1255), and for joints up to 30-in. (76.2 cm) diameter the recommended calculated.

3.1.7.4

actuator

DESTRUCTIVE

Destructive

testing

should

be

capable

of

developing

25

percent

TESTING shall demonstrate

join t failure

139

characteristics.

more

torque

than

The joint can fail in the mode can be demonstrated should

be mounted

angle

elastomer layers in an actuation

in an actuation

at various

pressures

up

or in the reinforcements bench test. The joint

bench

to

the

test

fixture

maximum

and

(sec. without

actuated

expected

2.1.5). Each failure the insulating boot

to the

operating

maximum

pressure

vector

MEOP.

At

pressures in excess of the MEOP, the vector angle should be increased in the ratio of the test pressure to the MEOP. Pressurization and vectoring should be increased at least up to the design ultimate pressure to demonstrate minimum compliance to motor requirements, and up to pressure producing joint failure usually identified by failure of the joint

3.1.7.5

AGING

The

joint

if the failure characteristics to maintain a pressure seal.

are required.

Failure

is

PROGRAM aging

program

shall

demonstrate

that joints

possess

acceptable

storage

life. Bench

tests

since

changes

should

be conducted

in joint

spring

on joints torque

that

have

been

formulation (sec. intervals and the

2.1.2.5.2). It is recommended spring torque measured. The

versus

time,

the

motor

specifications

and

3.1.8

Inspection

3.1.8.1

INSPECTION

The inspection initial ,material necessary

results

extrapolated

for the required

have

been noted

stored for

joints

service

using

environment,

a natural-rubber

that stored joints be vectored changes in spring torque should

to demonstrate

joint

in the

that

the

joint

at selected be plotted

will remain

within

life.

PLAN master plan procurement

to assure

shall incorporate through final

conformance

to design

inspection processes for use from joint acceptance to the extent

requirements.

Inspection processes should be used throughout the joint program beginning with material procurement and continuing through fabrication, process control, and final acceptance. Each phase :can use different inspection techniques with different acceptance or rejection standards. For this reason, an overall master plan for the use and management of the quality-control

program

the master plan and orientation master alertness planned

plan

should

of the

should

be established

prior

should be established on the basis of defects encountered, and the require

operators;

requirements

and

the

periodic

it should

evaluation

also provide

procedures.

140

to the

start

of fabrication.

The

scope

of

of the required reliability level, the type process sensitivity required. Also, the of the

for random

equipment checks

and on the

of the execution

skill

and

of the

Particular caution should be usedin planning the inspection requirements and in applying the inspection program so that material characteristicsand fabrication processesthat can affect the integrity of the inspection are identified. As an example, an inspection of elastomer thicknessthat is too infrequent could result in joints that weremarginalbecause of elastomerlayersthat varied in thickness.

3.1.8.2

INSPECTION

The

For the

For

PROCESSES

inspection

processes

reinforcements,

the



Spherical elastomer



Concentricity.



Thickness



Flatness.



Inner

the

shall

have

following

and outer

elastomer,

capability

minimum

radius at sufficient rings in a joint.

at various

the

inspection

positions

to

the

minimum

inspection

should

The

inspection

minimum deflection,

between

performance joints porosity

minimum

performance actuation, tests

should

be

inspected

the

dimensional end

attachment

rings,

inspections recommended and tensile-pressure seal

should taken

defects.

is recommended:

establish

expected

thicknesses

of

diameters.

su_faces,

concentricity

all critical

positions.

joint without adhesive on the reinforcement thicknesses and evaluate porosity visually.

recommended

of detecting

be

used

apart

to ensure

that

to verify

and

the

quality

cover then

for and

thickness

the

elastomer-to-reinforcement

141

joint

maintained.

is overall

flange-to-flange

envelopes.

porosity.

it. Measure

are the bench tests test (sec. 2.1.7.2).

clearance

is being

and

disassemble

At

Mold

a

elastomer

length,

parallelism.

the The

for compressive axial The data from the intervals, bond

production and

elastomer

3.2

LIQUID

INJECTION

3.2.1

System

3.2.1.1

SYSTEM

The

design

THRUST

VECTOR

CONTROL

Design

OPTIMIZATION of the

liquid

injection

system

shall be based

on a vehicle

optimization

study (including vehicle performance parameters, reliability, external constraints, and cost) that results in optimum vehicle performance. The recommended presented in chart

sequence of steps form in figure 47.

The design requirement based on a statistical allowance determined

for determining

because almost

optimum

should be defined as the maximum analysis of the operation of the vehicle

for the expected variation correctly at an early date

avoided, increases

the

envelope

LITVC

system

strongly side-thrust

affects impulse.

is

required vectoring capability on its various missions with

in the environments. This requirement and the use of inflated initial estimates

the vectoring requirement linearly with the required

design

the

design.

The

should should

system

be be

weight

The likely LITVC-system design options should be laid out without detail but should include basic design parameters such as type of injectant, injection pressure, source of pressurizing gas, number and spacing of orifices, injection location and angle, and tank type and

shape.

General

design

injector should

(including

motor

data,

candidate

injectant

specific

injection Initial

vehicle performance of these evaluations

configuration, design

amount

provide represent

the

of a system of data

tank should

for

LITVC

(e.g., should

range, payload, be used as the

shape,

and

be based

the pressurization on performance

systems

an empirical basis for design motor geometry and operating

final basis

is available

velocity), reliability, and for selecting the injectant,

data

(sec.

thrust

deflection

deflection angle

angle

be limited

cost. the

method. from

2.2.3.1)

previous and

programs.

should

be used

A to

analysis. The available data, however, will always conditions different from those of the motor for

which the new LITVC system is to be developed. Therefore, those data must or scaled to the geometry and operating conditions of the present motor section 3.2.3. The

impulses,

weight variation with flowrate, and tank weight variation with volume and pressure) be assembled. Each possible design choice must be evaluated in terms of its effect on

the desired The results

large

information

can be as much to 6 °, because

as l0 °, but the

142

efficiency

it is recommended as measured

by

be transformed as described in

that injectant

the

thrust specific

Define design requirements vectoring capability, motor meters, space envelope, constraints) .

Identify

the

(each option combination

LITVC

design

design

options

injectant, injector

loca-

available er'or i

ance data

data and to formulas

component and

weight curves

to

design

problem.

adapted

Determine

the

weight

and

capability option,

and

of each tion of

option on the rocket

Calculate

side-thrust

for each establish

the

(range, reliability,

payload,

for each optimum

option LITVC

Figure 47. - Recommended

and

will include one of design parameters

including type of injection pressure, tion, etc.).

i

(required para-

LITVC the

the configuramotor.

vehicle or

design effects

performance

final cost to system

as

velocity), required

determine design.

sequence of steps for determining

143

the

the optimum

LITVC

system design.

=.

impulse (refs.

drops 46,

3.2.1.2

to low

108,

and

The

The

shall

consistent

injectant

flowrates

required

for larger

deflections

deliver

maximum

with

material

side

specific

impulse

compatibilities,

and

storage

have

the

highest

requirements,

and

toxicity.

IX summarizes selection

high

OF INJECTANT

in]ectant

allowable

at the

122).

SELECTION

density

Table

values

_

the

of the

relevant

injectant

data

must

on the

consider

major the

operational

efficiency

injectants.

of the

injectant

in delivering

side

specific impulse. The relative efficiency of a candidate injectant may be known from existing data (secs. 2.2.1.2 and 2.2.3.1); if not, it should be checked by small-scale tests. Data on the relative efficiencies of various injectants are given in references 109, 121, and 141; figure 48 presents Isp(s) values for a number of inert and reactive liquids. The relative efficiency of a new injectant should be estimated from chemical-equilibrium calculations; various approaches and typical results are described in references 144, 145, and 146. Judgement make no injectants. injectant. and that

must be allowance

used in interpreting for the variation

the results in evaporation

of equilibrium calculations, rate and reaction time

Excessive time delay in energy release reduces the potential It is recommended that calculations be used only to screen the final evaluation be made by test firing.

since they of different

effectiveness of an injectant candidates

The injectant should be selected for highest density, so that the fluid tanks, valves, and tubing can be made as small as possible to save both space and system weight. A preliminary estimate should be made of the volume required for the liquid injectant, and the storage tank that will contain this volume should be designed and fitted around the nozzle so that the envelope

constraint

can be evaluated.

The liquid selected must long-term storage when kept of the Vehicle. As examples perchlorate in water boils at 70 ° F (294 should

not

propellants

crystalizes at temperatures K) at a pressure of one

be important

The compatibility neighboring systems on

places. If positive injectant cannot

not chemically decompose, evaporate, or crystalize during within the temperature and pressure limits specified for storage of typical limiting conditions, a 62% solution of strontium

with

of the should

contact.

sealed

systems

under

candidate injectants be checked, because

Danger

to

personnel

approaching atmosphere

32 ° F (273 K), and hydrazine (ref. 115). The latter limitation

pressure. with certain

may

be

the motor, propellant, reactive injectants ignite important,

especially

and other some solid in

safeguards against inadvertent spillage of an effective but highly be provided, then the injectant will have to be eliminated

144

confined reactive from

The for

Isp(s ) listed the following ,250;

emj=

is for typical booster stages (Pc _ 800 conditions: single orifice injection;'Pin

2.5;

Fs/F a

= 0.02

psia, j =

e _12) 1800 psia;

.

320 --

UDMH

+

N2H 4 (EXOTHERMIC

DECOMPOSITION)

Decomposition _.._under /These /difficul_

280

--

MHF-3

occurs

only

certain conditions. I s- values are to achieve.

(EXOTHERMIC

DECOMPOSITION)

240 NITROGEN

TETROXIDE

--

200

HYDROGEN

STRONT LEAD

PEROXIDE

IUM

PERCHLORATE

PERCHLORATE

+

+

METHANOL

WATER

MHF-3

1--

FREON 12, BROMINE

120-FREON

I14-B2

(INERT)

--l---

UDMH

+

FREON

113

(INERT)

N2H 4

N ITROMETHANE UDMH

--

FREON 114-12 (INERT) P E RCHLOROETHYLENE

l80--

BENZENE

I-

ISOPROPYL IRFNA ZINC WATER

40

ALCOHOL

(ENDOTHERMIC BROMIDE OR

DECOMPOSITION) IODIDE (INERT)

(INERT)

I

Isp(s

Injectants performance

Figure

48.

for is

- Values (data

which well

of from

),

lbf-sec/lbm

Injectants

TVC

performance

defined

side refs.

specific 121,125,

impulse and

145

for 129).

reactive

for is

and

which

TVC

not

well

inert

liquid

defined

injectants

consideration. For example, a toxic fluid such as nitrogen tetroxide or bromine shouldnot be selectedunless it is practical to provide protection to personnel and the environment during loading, checkout, ground testing, launch, and possibleother releasedue to mishap. The liquid must be compatible with every tank or bladder material with which it comesin contact. The tank or bladder materials must neither react with the liquid nor catalyzethe liquid's decomposition. The materials should resist decompositionby the liquid and remain impermeable,becauseliquid that has permeateda material is not available for injection. Resultsof investigationsof the permeability of variousbladdermaterialsgiven in references 115 through 118 should be consulted.

3.2.1.3

INJECTION

The

PRESSURES

injection

the orifices

pressure, shall

the

For

greatest

control orifice being tests.

orifice

maximize

The most efficient pattern circumferential line on the efficiency,

AND

INJECTION size,

the side

for injection nozzle wall

these

orifices

and

thrust

circumference

be estimated

number,

should

for minimum optimization

injector weight

and

of

have

omniaxis

control

orifices located in a 121, 124, and 125). rather

than

pitch-yaw

overlap losses should be 7 to 14 times the be studied and transformed to the system

If this is not possible, the spacing effect should be evaluated that cosine losses due to spreading the orifices around by vector

addition

system weight should be compared with pressures, and the overall optimum pressure three-orifice

and grouping

is obtained from many circular (figs. 29 and 31 and refs. 109,

of the

estimated

The injection pressure should be about twice the rocket side-thrust specific impulse (figs. 38 and 40 and refs.

The

spacing,

efficiency.

(ref. 142). Minimum spacing to avoid diameter, but the available data should designed (sec. 3.3.3.1). It is recommended

the

ORIFICES

since

simple

but

plumbing,

it provides this

effects.

chamber pressure to achieve highest 108 and 121). However, hardware

loss in side-thrust should be used.

is recommended,

side-force

in the

efficiency

excellent

effectiveness

must

for

lower

side-thrust

injection

efficiency

be confirmed

by an

study.

The simplest LITVC injector arrangement has four injectors 90 ° apart. However, thrust deflection may be required in any plane, not just the pitch and yaw planes. In this event, the side force is the vector sum of the forces produced by the two injectors. Two such injectors operating single

simultaneously

injector

As noted flowrate

to produce

will use injector the

previously, injection or side-force level,

same

liquid

at a rate

approximately

_/_'times

that

of a

side thrust.

is more efficient the number of

146

at low flowrates per injectors is increased,

orifice. then

If, for a given the side-thrust

efficiency is increased.The efficiency of a number of injectors usedto produce a singleside force is estimated by vector addition of their side-force contributions. Each injector is considered to produce a side force at its location independent of the adjacentinjectors. Therefore,the efficiency of multiple-injector LITVC can be estimatedfrom the equation

Cosineefficiency =

(12) n inj

where llin j =

I_/i

=

number

of injectors

angle between injector

operating

total

side force

and

the

side force

produced

Equation (12) does not include the efficiency increase due to reduced or efficiency decrease due to overlapping of adjacent mixing and shock

3.2.1.4

INJECTOR

The injector

LOCATION location

AND

DISCHARGE

and discharge

angle

side-thrust

For highest side-thrust efficiency, locate the injection orifices nozzle as is possible without incurring significant corss-nozzle vector deflection. (Cross-nozzle effects are pressure increases

(1)

Use the empirical

ratios

for X/L

listed

(refs.

X/L

Nozzle Small thrust deflection (about I °)

17.5°

0.3

0.4

27.5 °

0.2

0.3

Large thrust deflection (about 6° )

X = distance (along nozzle axis) from throat to point of injection

147

efficiency.

over.) One or more of location of the injector

108 and

divergence half-angle

L = distance from throat to nozzle exit plane

per injector

as far upstream in the rocket effects at maximum thrust on the wall of the opposite

that cross the optimum

below

Optimum

flowrate areas.

i TM

ANGLE

shall maximize

side of the nozzle caused by shocks and injectant following three methods should be used to estimate the nozzle exit-cone wall:

by the

125)"

the on

(2)

Estimate

the

Generate such that

a straight the line

curves

optimum

Use the

methods

shock

and

injector

location

by

use

of

empirical

curves

49. The

injection

point

at which

site (refs.

of fluid

mechanics

injectant-mixture

the line reaches

107 and

only

49).

and gas dynamics

disturbance

the

nozzle

for inert

wall is the

147).

in the

to estimate

nozzle

from

the path various

injection points; however, check the method selected against known before it is applied to the design problem. One such method utilizes computer program (ref. 151); however, in its present form the formulated

(fig.

line from the nozzle rim opposite the proposed injection point crosses the nozzle centerline at the angle X obtained from the

for _ in figure

probable

(3)

optimum

of the possible

test results the Boeing program is

injectants.

The optimum discharge angle (figs. 23 and 37) results in the greatest collision effect and mixing of the motor gas and injectant. From various studies (refs. 107, 108, and 125), the discharge angle should be 25 ° . However, as the discharge angle influences the location of the injectors and the discharge evaluated

3.2.1.5

their plumbing, envelope angle. For systems that

be a factor in the selection the discharge angle should

of be

by test.

AMOUNT

The

considerations should must be an optimum,

OF LIQUID

amount

maximum

of vehicle

liquid flight

INJECTANT

in]ectant duty

shall

REQUIRED be the

minimum

amount

necessary

for

the

cycle.

The weight of liquid injectant required must be calculated from the maximum required vectoring capability of the motor, the injectors and their location having been selected as described in section 3.2.1.4. The vectoring requirements will be given explicitly as thrust deflection The

angle

following

(1)

0 for

procedure

pitch

and yaw

is recommended

and

required

side thrust

for calculating

Fs, each

the weight

as a function

of injectant

of time.

required:

For each candidate liquid injectant, determine the side specific impulse Isp (s) as a function of deflection angle, and plot the results. Examples of such plots are given in figure

42.

(2)

Noting the motor vectoring requirements time t, use the results of item (1) to obtain function of time.

of deflectionang!e 0 as a function the estimated side specific impulse

of as a

(3)

Noting the motor side force requirements injectant weight flowrate _¢_ as a function

F_ as a function of time.

the

:

148

of time,

calculate

60 ° I

=25 °

50 ° __.__.__.----I

_

v

4oO

,[

0 ¢0 0 0

30 ° --

t4 0 4-I

qJ p-4

20 °

10 c __

O,







Largest

Notes:

'

'

The rim

required



deflection

diagonal from the injection is not the location of the





angle

0ma x

port shock

to the nozzle wave (cf. fig':23).

Figure is based on data from conical and contoured nozzies having e= 7 to 20, _ =18 to 28°,and _ both inert and reactive injectants.

Figure 49. - Relation

of thrust

deflection

angle to injector location

149

(refs. 107 and 147).



Integrate estimate

(4)

the injectant the amount

determine

the

achieve The

(5)

The

the

of injectant

gas flow

of

of the

for the injector and transformed

the

injectant

liquid

side impulse

into

the tank warm-gas

cold

gas under

required

success.

for vectoring,

including

that

and valve vectoring.

for tank

ullage,

leakage, must be For preliminary

should

be carefully

estimated

for the motor

being

tank

within

of liquid

shall

expel

the liquid

the specified should

generator,

high

GAS REQUIRED

or

pressure

be from the

at a rate

response

gas

is the

a tank can

be

source

that will produce

time. of compressed contained

of the

inert with

gas used

gas or from

the

liquid

pressure be sufficient

The ......... of regulator so that

tank

may

a

in

to pressurize

gas should have a volume at LITVC operating pressure equal to the total volume, the volume of the piping and the manifold, and volume of liquid

in the

to

purposes.

OF PRESSURIZATION into

angles

to to

configuration and location selected by use of available test for application to the current design problem (sec. 3.2.3).

expelled. Because the specified injection point and be sustained acceleration and flow friction injectant should

available

10% for these

impulse

solid-propellant common tank.

injectant

not

of flight

deflection

add

gas flow

liquid, the own stored

probability

for the various

estimates,

AMOUNT

If a tank

of side impulse

ignition to the end of firing or use statistical methods

piping and valves, and for valve operation and added to the amount needed for

the required The

_Vs from motor injectant required,

for filling calculated

designed and, data, correlated

The

amount

specified

amount

side specific

3.2.1.6

flowrate of liquid

a

the of its to be

injectant pressure must be delivered to the fluid at the during sudden demands for large flows, the effects of liquid should be evaluated. The pressure applied to the liquid

have,

to

be

significantly

higher

at the injector valve. The piping sizes, to respond to the worst conditions.

the

than

the

gas supply

minimum

required

rate,

pressure

and

the gas delivered to the liquid tank should be reduced by a pressure liquid is not injeCted at pressures excessively above the pressure level set by

the design. The real

weight of gas so required should be calculated from one of the equations of state of a gas, such as the Beattie-Bridgeman equation or the equation of state with

compressibility factor contained in reference error

(ref. 152). An example of such 153. An estimate of the weight

< 10%, can be obtained

from

the ideal-gas

150

equation

a calculation for a LITVC system of the gas required, usually with of state:

is an

CPM p

-

(13)

RT

where p = density,

lbm/ft

P = pressure, M = molecular R

= universal

T = absolute

generator

3)

psia (N/m 2) weight

of the gas, Ibm/ibm-mole

gas constant,

1545.3

temperature,

C = conversion

If a warm-gas

3 (kg/m

lbf-ft/lbm-mole-°R

(8314.3

J/kg-mole-K)

°R (K)

factor,

is used

(kg/kg-mole)

144 in. 2/ft2

in place

of cold

(1 J/N-m)

compressed

inert

gas, a larger

total

quantity

of gas will be required than that calculated above. This condition arises because the supply of gas must be maintained at the maximum expected demand level through all periods of firing time, even though the actual demand for pressurization gas usually will be much lower than the maximum. The propellant grain in the warm-gas generator must be designed to produce vectoring overboard

sufficient

pressurizing

requirements (ref. through a pressure

gas

to

cause

154). The gas that relief valve.

the

injectant

is produced,

to but

not

If a common liquid/gas tank with no separation between the allowance should be made for the dissolving of part of the evaporation for example, N204

the real

of some in the

vapor methods and

not

with

used,

should

ideal

properties

of dissolving and evaporating of mixtures (ref. 152). Care of the

gases

in order

to avoid

the

motor

be released

liquid and the gas is used, gas in the liquid and for

of the liquid into the gas. The latter phenomenon Titan III system at 70 ° F (294 K), the pressurizing

(ref. 47). These effects of the thermodynamics the

comply

usually is negligible; N2 contains 1.5%

should be calculated by should be taken to use the substantial

errors

at high

pressures.

3.2.2

Component

The

size

represent

Design

of LITVC

components

the LITVC

system

shall

be based

to be designed.

151

on

verified

empirical

curves

that

The empirical curvesmust provide adequatedata of sufficient accuracyfor selectionof type of injectant fluid, injector location, number of orifices, injection angle, and injection pressure.Any additional data required must be generatedfrom subscaletests (sec.3.2.3.2). These curves must be based on test data, becauseavailable analytical methods do not reliably predict LITVC performance. Data for these curvesshould be obtained from earlier developmentprograms and subscale tests.These data should be plotted and correlated, then transformed for usein the current design(sec.3.2.3.1). After the first complete set of LITVC components has been designed, it should be fabricated, assembled,and evaluated in a full-scale test (sec. 3.2.3.3) at the earliest opportunity to confirm the design and to verify performancedata for usein further design improvementor performanceprediction.

3.2.2.1

INJECTORS

Injectors

shall

velocity

within

deliver

injectant

the required

The injector valves should flowrate as determined by satisfactory

accuracy

to the

response

be sized methods

for design.

The

exhaust time.

flow

in columnar

jets

at maximum



no larger described

than necessary for the in sections 3.2.1.3 and

injectors

must

contain

flow

maximum required 3.2.1.4; use data of

passages

and

orifices

that

are specially contoured and streamlined to accelerate the fluid to the maximum possible velocity on discharge. The pintles or gates must likewise be contoured and streamlined to achieve maximum acceleration of the fluid, so that on discharge the fluid is travelling at the highest

obtainable

pressure

The use of variable-flowrate side-thrust Off-on

center-pintle capability

injectors

vectoring (ref.

that

as little

to injection

as possible.

be

control

preferred

in

with

different

of actuating response,

the

from the inert

the natural

shock

cases

injector weight

frequencies

valves

must

penalty,

cost

76).

152

way,

or electro-mechanical these injectors can

minimal

certain

In this

the

system

momentum.

type injectors with servo is recommended, because

and versatile may

diverge

converted

because

These injectors should be of the center-pintle when fully open. To avoid vibration problems,

be set in a range method

in jets

efficiently

efficiency

simplicity. momentum

The

speed

will be most

of

their

of the structures

constraints,

for high

weight

and

loading.

type designed their operating

be determined

control provide

from and

low

for maximum flow frequency should of the vehicle.

the required

flight

control

speed limitations

of

Screensshould be installed in the liquid supply entranceto eachinjector valveto catchand hold any debris that might causetrouble in the injector valve. Measuresfor the control of contamination of fluid, components, and system may suffice in lieu of active screensor filters.

3.2.2,2

STORAGE

The

liquid

TANK in]ectant

during vehicle operation.

AND tank

storage

BLADDER shall

preserve

and provide

positive

The shape of the tank should of injectant to be carried

be selected should be

recommended

that,

amount

spherical

be used,

tanks

if

the

because

the

the

liquid

without

expulsion

of the

degradation liquid

to result in minimum weight. determined as described in

of

liquid

sphere

required

is the

most

shape;

during

motor

The required amount section 3.2.1.5. It is

is relatively efficient

or loss

small, but,

one

or

if a large

more

amount

of liquid must be carried, the tank should be toroidal, since this is the shape with the largest volume that fits around a nozzle. In intermediate cases, cylindrical tanks are suitable. The tank should be designed according to the recommended practices of reference 155, fabricated from a lightweight or high-strength alloy such as aluminum or stainless steel, and be compatible with the liquid. If the tank is to be left pressurized during storage or standby conditions when personnel may be near, the tank must be designed to meet the prevailing pressure-vessel safety code. To avoid this requirement so that a low factor of safety can be used, provision should be made to pressurize the tank when the vehicle is prepared for launch and after personnel have been cleared from the vicinity. If

a cool

depended be allowed

inert

gas

is used

for

pressurizing

upon to keep the liquid puddled to contact the liquid directly.

A bladder to separate the gas from warm gas, because the gas loses replenished

by

more

warm

gas.

if gravity the

outlet,

or

acceleration

reactive

injectants

forces

it is recommended

the liquid is recommended if the liquid heat to the liquid rapidly, contracts,

With

provide a positive seal because contact combustion or explosion in the tank. and plastic.

and over

and

warm

gas,

that

can be the gas

is pressurized and must the

bladder

by be must

between liquid and gas could result in failure through The bladder should be fabricated from laminated fiber

Special means should be provided to completely seal the injectant liquid in the tank. The filling and trapped-gas vent fittings should be designed with provision for positive closure (e.g., crimped or soldered metal closures). The tank outlet should be sealed with a metal diaphragm 156).

scored

to break

open

without

loose

153

fragments

when

the liquid

is pressurized

(ref.

3.2.2.3

PRESSURIZATION

The

SYSTEM

pressurization

injectant

When the LITVC in time for the high-pressure

within

shall, the

study The

system

the

pressure

prescribed range

time,

the injectant must be brought signal. The pressurization a warm-gas

given

tank

in section

system

pressurize

for injection

generator.

The

into

the

the nozzle.

up to operating system can be

choice

that considers pressurization system performance capacity of the pressurized-gas storage volume

to practices

If a high-pressure

or

within

design

system is activated, first vector-control

inert-gas

optimization performance. according

system

to a level

should

pressure either a

be based

and weight should be

on an

and LITVC determined

3.2.1.6.

is used,

the

tank

outlet

should

be sealed

by a squib

valve that

is opened by an electric signal or system activation. The gas flow from the high-pressure tank should be stepped down to the design injectant pressure level by a pressure-control valve. If there is any possibility that harmful debris might come from the tank, valve, or line, screens should be installed ahead of the controller. An inert gas such as nitrogen should be used weight unusual If

a

in a high-pressure

tank

system

to minimize

corrosion

is important, helium should be used, but special ability of helium to diffuse through materials (ref. common

liquid/gas

tank

optij..n_m for the system. liquid is used should be deflection.

is to

be

used,

the

range

and

compatibility

attention 118).

should

of pressures

and be

be given

provided

Also, the minimum pressure remaining when sufficient for effective injector-valve operation

Warm-gas generator systems usually employ solid propellants solid rocket motors. The warm-gas generator should

problems.

to the

should

almost all and thrust

If

be

of the vector

are designed like miniature designed to deliver the

gas-flowrate/time profile that is calculated as described in section 3.2.1.6 and reference 157. The propellant grain shape should be adjusted to cause the flowrate to vary to fit the desired curve (ref. 154). Usually a high rate is needed initially to provide for launch or staging pertubrations;

this

condition

is followed

when only vector trim and course generator should be a clean-burning 1922 K)) propellant alloy-steel tubing and will be usable only if safe levels. Otherwise The gas pressure

by a period

of low demand

corrections are needed. low-flame-temperature

during

the

rest

of flight

The propellant for the warm-gas (2000 ° F to 3000 ° F (1367 K to

that does not produce deposits and that is not too hot to use with valves. Propellants that burn at temperatures above 2500 ° F (1644 K) the operating period is short enough to limit heating of steel parts to insulation or high-temperature metals will have to be used.

flow from the generator should regulator designed to step down

pass through the pressure

(ref. 156). Since the production of gas by the generator of actual gas demand, the surplus gas must be diverted

154

a screen to catch debris and into a to the design injection pressure level is predetermined and independent through a pressure relief valve for

disposalto the environment. If possible,this unneededgasshould be releasedfrom a small nozzle pointed aft, so that a small increment of thrust canbe recoveredthrough its release. However, if the vehicle has a coast period and if the gasgenerator bums after the rocket motor has burned out, the small exhaust jet could cause unwanted changesin vehicle attitude. This condition should be preventedby exhaustingthe unneededgasthrough two equal orifices that areoriented in opposite directions. If the main vehicle system requiresa supply of gasfor roll control, the possibility of using the samegasgeneratorfor this purposeand for LITVC pressurizationshould be considered.

3.2.2.4

LIQUID

Flow

from

vehicle

If there prevent

STORAGE

and

inertial

is more offsetting

EQUALIZATION

sloshing

in multiple

tanks

and

large

lateral

than one tank, provision must the vehicle center of gravity.

be made Uniform

to drain expulsion

tank is dependent on the ability of the bladder to deflect circumference of the toroid during expulsion. The bladder so that one sector freely movement could generate

3.2.2.5

DISPOSAL

collapses on the liquid undesirable sloshing,

OF SURPLUS

injectant

flow

shall not

change

rate

should

the tanks at equal rates to of liquid from a toroidal

and fold uniformly around the should not be allowed to buckle

while other the sloshing

sectors should

are restrained. be inhibited

If vehicle by baffles.

INJECTANT

Injection system destgn shall provide flight weight and to obtain additional

The

tanks

properties.

for disposal thrust.

be measured

and

of surplus

integrated

over

injectant

time,

so that

to reduce

at any instant

of flight time the total amount of liquid actually used will be known. A computer or control device should continuously compare the amount of liquid used with the maximum that could

be

control nozzle The

used

up to that

time

without

jeopardizing

the

completion

of the

mission.

should then signal the injectors to expend the excess liquid equally around so that the motor thrust will be augmented but there will be no thrust deflection.

axial

thrust

added

by jettisoning

the surplus

expression:

155

liquid

can be estimated

with

Flight the

the following

aFa =

lsp(s ) (o = o*) Ws tan

a

(14)

inj

where /kF a

lsp(s)

(o

= axial

thrust

= specific

= o°j

impulse

deflection, lb f-sec/lbm = flowrate Odlnj

This

equation

added

by surplus

injectant,

of the liquid

estimated (N-sec/kg) of liquid

from

injectant,

lbf (N)

injectant a plot

in the side direction

of Isp (s)versus

lbm/sec

0 (e.g.,

at 0 ° figs. 35 and 42),

(kg/sec)

= the equivalent half angle of the nozzle from the injection point to the exit, determined as the angle between the nozzle centerline and a line from the injection point to the exit rim, deg

is applicable

to both

extrapolated to 0 ° deflection augment axial thrust. These

angle effects

conical

and

contoured

nozzles

(ref.

126).

The

Isp(s

)

is used because it best represents the LITVC effects that are the increased pressures on the exit cone caused by

injectant energy and mass and by injection shocks. I_p (s) values obtained at larger deflection angles should not be used in equation (14) because these Isp (_) values have been reduced by losses in measured side forces due to the circumferential spreading of the side forces around the nozzle. Such losses detract from side thrust but not from axial thrust. Correlation the data in reference 121 shows an accuracy within -+ 10% for nozzles with expansion

with ratios

up to 10. Equation (14) may underestimate the added thrust when applied to long contoured nozzles having expansion ratios greater than 20 with injection far upstream from the exit. This result occurs because the wall angle at the center of this region of added pressure usually is significantly pressure nozzles,

larger

than

the

equivalent

half-angle

OLin j.

The

center

of the

region

of added

generally is located a short distance downstream of the injection orifices. then, the value for the half-angle used in equation (14) will be less than

For such the local

wall angle at the injection point but greater than _inj as defined above; this effective half-angle is estimated from experience. The added thrust due to expending injectant in the nozzle is more accurately estimated by the use of data from subscale tests or, if an adequate mathematical model exists (sec. 2.2.3), by integrating the product of the added pressure and the tangent A detailed

of the

wall angle

performance

over

analysis

the

nozzle

wall

of a liquid-injectant

47.

156

area

affected. dump

system

is presented

in reference

3.2.2.6

ADAPTATION

The

motor

for system

OF THE

design

shall

MOTOR

provide

FOR

injector

LITVC

mounts

and ports

and

external

brackets

support.

The nozzle design should make provision for holes and mounts for the injectors. The metal orifice ends of the injectors should be recessed sufficiently inside the injection port (fig. 29) that they will not be damaged by heat flux. The heat flux at the inside end of the injection port should be estimated (refs. 134 and 135). The port hole should be made conical to fit the shape of the liquid jet and only large enough to permit the jet to be discharged without momentum losses due to wall friction. Small port hole size will minimize heat transfer into the

hole

and

the

exhaust-gas

Provide liner.

will minimize

erosion

at the

hole

edges

that

results

from

impingement

of

flow.

a gas-tight

The injector wail should

the

seal such

as an O-ring

mount, to which the have sufficient strength

at the interface

between

the

injector

and

the nozzle

injector will be bolted, and its attachment to the nozzle to withstand the full injector reaction thrust in addition

to other loads. If possible, the entire LITVC system should be mounted on the nozzle avoid any problems of differential motion between the nozzle and the motor aft dome skirt. If this mounting is not possible, provide flexible lines or expansion joints.

Mechanical and thermal analyses made of the nozzle and related LITVC

system

the major part these vectoring

The

only

that

occurs

and

to the

(i.e., stress, gas flow, heat transfer, and erosion) should be portions of the motor. Loads due to the weight of the

intermittent

TVC

Pressures

on the

of the vectoring force must be included in these pressures on the exit-cone wall can be estimated

thermal

problem

around

and

of consequence immediately

to or

due

downstream

to LITVC of the

exit

cone

walls

analyses. The (ref. 136).

is the

severe

injection

port

that

heating holes

produce

distribution

of

and erosion (fig.

34).

The

amount of erosion depends on the exhaust flow properties, the reactivity of the injectant, and the type of ablative material used. To predict this erosion, use methods for predicting erosion that include the capability for treating the effects of chemically reactive injectant and exhaust-gas mixtures (refs. 158 and 159). The analysis should be cross checked by scaling known LITVC hole erosion to the relationships being used as the scaling factors. typical

heating

and erosion

patterns

is shown

design condition, appropriate heat-transfer A design of an injector mounting pad with in figure

157

50.

Injector surface

Eroded

mounting-pad

surface

V/I/I//lllA

7075

aluminum

alloy

silica/phenolic Graphite

cloth/phenolic

Figure 50. - Typical LITVC port configuration showing erosion and char patterns.

3.2.3

Performance

Test

data

shall

operational Test

data

from

be

demonstrated

3.2.3.1

support

the

and Testing

LITVC

system

development

and

demonstrate

capability. other

being designed determine the should simulate

Evaluation

LITVC

should general

systems

be used configuration

transformed

for

supported by data from actual motor conditions. at test

conditions

PERFORMANCE

Performance to the LITVC

data

from

system

other

FOR

actual

correlated

by analysis

to the LITVC

design and motor tradeoff system. As soon as possible,

subscale tests The full-scale

simulating

DATA

and

conceptual of the motor

conducted under motor operating

flight

studies to these data

test conditions that capability must be

conditions.

DESIGN

LITVC

programs

required..

158

shall

be demonstrably

applicable

Existing LITVC data that canbe transformedto the required LITVC systemshouldbe used for motor optimization studies,tradeoff studies,and preliminary conceptual design.These studiesmust be conducted early in the program to determinethe adequacyof the data and to define neededadditional data so that a test programcan be commenced. The data obtained from various sourcesmust representthe variation of side-force specific impulse with injectant flowrate, injector location, injection angle,injection pressure,orifice size, and orifice spacing.The available test data should be transformed to dimensionless form except for the side-force specific impulse, which is retained in units of lbf-sec/lbm (N-sec/kg). Each of the designvariablesshould be presentedas a family of curves,wherein all other parameters are constant at one or more arbitrary configurations. These configurations should be selectedto representarange that includesthe optimum design.An example of this practice is shown in figure42 for an evaluationof injection pressure.Other plotting formats as illustrated in figures 36 through 40 should be used if they are more convenient. Data that have originated from rocket motors that were significantly different from the designmotor should be transformed; use the dominant physical lawsasdescribed in section2.2.3.1 to make them applicable. The suitability of the transformed data to the design motor must be evaluated for consistencyand agreementby using data from different sourcesplotted on the samegraph. If the results form a continuous plot with little scatter, the results can be usedwith confidence. If the scatter is larger than can be tolerated within designspecifications,a test program must be initiated to generatedata in the expecteddesignrange.Awaiting test data could result in a delay in a program, and in such a period the transformeddata will be the only availabledata. Thesedata must be usedfor initial optimization studiesandpreliminary design;useengineeringjudgement to allow for an amount of error defined by data scatter. The results obtained with such data must be reevaluatedwhen test data in the expected designrangebecomeavailable.

3.2.3.2

SMALL-SCALE

Small-scale provide Small-scale transformation injection the test

tests

design tests

TESTS using

data not

should of other

system

parameters

otherwise

available.

be conducted test data. The

in

to obtain test motors

the

expected

data should

design

that are use rocket

range

shall

not available nozzles and

from LITVC

geometries that are scale models of the expected full-scale design configuration; motor chamber pressure should be the same as that of the design motor; and the

test propellant exhaust gas should be similar to that of the full size motor in temperature and in oxidizing species that are free to react. To obtain valid data, the test motor need not be a solid-propellant motor but can be a liquid propellant motor, a change that usually results

in cost savings

and

test

convenience

(ref.

159

121).

3.2.3.3

FULL-SCALE

A full-scale An

firing

evaluation

of the

DEVELOPMENT

TESTS

test shall evaluate

the LITVC

full-scale

LITVC

system

system

should

design.

be conducted

on

the

first

static

test

firing of the motor, so that design changes can be incorporated without causing significant program delays or increased costs. Measurements must be made of all parameters affecting design of the LITVC system and the results used to reevaluate the injector valves, injectant requirements, and injectant tank size. If the motor is to operate at high altitude, the test should be conducted at the corresponding ambient pressure. The final LITVC design must be evaluated in static test firings, so that its actual performance and characteristics can be known

for flight-control

may be necessary

3.2.3.4

use. Vertical

OPERATING-CAPABILITY

Procedures operation

orientation

of the motor

or at least

of the liquid

tanks

for such-tests.

for

the

TESTS

component

of the LITVC

system

testing,

assembly

shall be developed

installation, and

checkout

and

documented.

The functional capability of all components of the LITVC system should be determined by test before assembly. These tests should employ pressurized gas and liquid supplies and control connections as necessary to simulate operating conditions. The bench testing should be performed with an inert liquid (e.g., Freon) clean. If a reactive or nonevaporating injectant thoroughly

cleaned

after

testing.

After the system has been should be checked during satisfactory documented. The

other

that will evaporate and leave the components is used in bench testing, components must be

operating The critical

assembled and installed on the motor, storage or launch readiness as often

capability. components

components

including

Procedures for these are the gas pressurization the

meters,

check

piping, and fittings are important but they are not procedures for correct installation, filling, operation, the rocket motor should be documented. If a gas generator is used, and resistance. If a tank pressure checked The

more

monitored

gage, should for continuity sensitive

be monitored, and resistance.

electric

by feedback

the igniter squib should of inert gas under high

portions

and

of the

the

squib

injectors

signals.

160

valves,

the critical components as necessary to ensure

check operations subsystem and injectant

should be the injectors.

tank

and

bladder,

nearly as sensitive to malfunction. Also, and unloading of the LITVC system on

be checked at low voltage for continuity pressure is used, its pressure, sensed by valve

should

at its outlet

be actuated

should

be electrically

and their

movements

APPENDIX Conversion

Physical

quantity

of U. S. Customary

U.S. customary

Angle

degree

Density

lbm/ft

Force

lbf

unit

3

A Units

to Si Units

SI unit

Conversion

radian

1.745x10

kg/m 3

16.02

N

4.448

factor a

-2

t

in.

cm

2.54

ft

m

0.3048

lbm

kg

0.4536

Ibm/Ibm-mole

kg/kg-mole

1.00

Peel strength

lbf/in.

N/cm

1.75

Pressure

atm

N/m 2

1.O13x10

psi

N/m 2

6,895x103

psi

N/cm 2

0.6895

lbf-sec/lbm

N-sec/kg

9.80665

Stress

psi

N/m 2

6.895x103

Temperature

oF

K

oR

K

K= 5(°R)

oF

K

K= 9"_--(°F )

oR

K

K = 95---(°R)

in.-lbf

m-N

0.1 130

Length

Mass

Molecular

Specific

weight

impulse

Temperature

Torque

difference

s

K:-_9(°F

+ 459.67)

aMultiply value given in U. S. customary unit by conversion factor to obtain equivalet_t value in SI unit. For a complete listing of conversion factors, see Mechtly, E. A.: The International System of Units. Physical Constants and Conversion Factors. Second Revision, NASA SP-7012, 1973.

162

APPENDIX

B

GLOSSARY*

Definition

Symbol A

Appears

reinforcement material constant value of elastomer shear modulus superimposed

eq. (3)

pressure

C

conversion

d

distance from point of liquid nozzle exit, in. (cm)

do

diameter

of the discharge

injector,

in.,(cm)

factor,

throat

t44 in. 2/ft2

diameter,

eq. (13)

injection

orifice

dt

nozzle

E

hoop modulus of elasticity ment, psi (N/m 2)

F a

axial component lbf(N)

U S

affecting with

In

to

of the

in. (cm)

figs. 39 and 42

fig. 36

of reinforce-

of the rocket

fig. 43

motor

fig. 19

thrust,

figs. 35,

36, 37,

38, 39, 40, and 42 and eq. (14)

side force due to liquid injectant, i.e., component of the total rocket motor thrust perpendicular to the motor axis,

figs. 35 - 42

lbf(N) G

effective subjected

G o

elastomer to external

shear

modulus

pressure,

elastomer secant shear modulus (3.45 x 10 s N/m 2) shear stress

when

at 50 psi and no

externally applied pressure, at the temperatures expected in operation, psi (N/m 2) Divided into three sections:

Symbols, Material Designations,

163

eqs. (2) and (3)

psi (N/m 2)

and Organization

Abbreviations

eqs. (1), (3), and (6)

Def'mition

Symbol lsp(s)

side specific

impulse,

Appears

ratio

of side force

produced by injectant to injectant flowrate causing side force, lbf-sec/lbm (N-sec/kg)

integral

i@

values

ible-joint I _1)

and 1 032)

for calculation

of

table VIII, figs.40 and 48, and eq. (14)

table

fiex-

In

V

:

spring torque

integral

values

at angles

eq. (1)

fll and/_2,

respectively

I% i¢,

correction

factor

a function

of cone angle

correction

factor

a function

of cone angle

distance

L

from

plane,

weight

Ibm/Ibm-mole Math

Mini

eq. (7)

to reinforcement

nozzle

fig. 18 and

stresses,

throat

stresses,

to nozzle

exit

in. (cm)

molecular

M

to elastomer

number

at the point

of pressurization

gas,

,

fig. 18 and eqs. (9) and (10) figs. 35, 36, 37, 38, 39, and 42 eq. (13)

(kg/kg-mole) of the rocket of secondary

expected

exhaust

gas

fig. 43

injection

MEOP

maximum

operating

pressure

MS

Margin of Safety: fraction by which the allowable load or stress exceeds the design

text eq. (5)

load or stress, MS -

number

n

1 R

of elastomer

1

rings in a flexible

joint number

ninj

P

Pal/l

Pc

b.

of injectors

operating

eqs. (6), (9), and (10) eq. (12)

pressure,

psi (N/m 2)

eq. (13)

ambient

air pressure

fig. 36

motor pressure: bustion chamber

pressure in the comof the rocket motor

eqs. (4), (7), and (9), figs. 25, 36; 38, 39, 40, 42, 43, and 48

164

Definition

Symbol

liquid injectant injector valves

Appears In

pressure

delivered to the

figs. 35,36138_ 40, 42, and 43

39,

static pressure of gas flow in the nozzle

fig. 25

static pressure of gas flow in the nozzle at the injection location

fig. 43

QLS

quadruple

various places in text

R

(1) ratio of design load or stress to the allowable load 0r stress (2) universal gas constant, lbf-ft/lbm-mole °R (J/kg-mole-K)

eq. (5)

inner joint radius

fig. 12

outer joint radius

fig. 12

pivot radius of joint measured from geometric pivot point, in. (cm)

fig. 12 and eqs:: (6), (7), (9), and (10)

Ps

_,ai

Rp

- lap shear:

eq. (13)

Ro+Ri 2

Rp-

eqs. (1) and (2)

ri

Rp -

nte/2

ro

Rp + nt_/2

eqs. (1) and (2) J

T

absolute

eq. (13)

Tq

flexible-joint (m-N)

temperature, °R (K) spring torque,

eqs. (1) and (2)

in. - lbf

• ,r,.

Ts,

inj

static temperature of the gas flow in the nozzle at the point of injection, °R (K)

fig. 43

time from start of motor

calculation procedure in sec. 3.2.1.5 ,



t_

A

thickness of elastomer

operation,

ring in flexible

joint, in. (cm) tr

thickness

of reinforcement

joint, in. (cm)

165

in flexible

sec

figs. 12 and 19, eqs. (6) and (7) figs. 12 and 19, eqs. (6), (7), and (10)

Definition

Symbol Vinj

velocity point

AppearsIn

of gas flow in the nozzle

of injection,

weight

flowrate

the rocket

ft/sec

fig. 43

(m/see)

of the exhaust

motor,

at the

_ '_ i :

lbm/sec

gas from

figs. 36, 38, 39,40, and 42

(kg/sec)

weight flowrate of the injectant injector into the rocket nozzle,

figs. 39, 40, and 41

from the lbm/sec

and eq. (14)

(kg/sec) X

distance

measured

line from containing ports, O/

O/1

O/inj

along

the nozzle

the nozzle throat to a plane the centers of the injection

divergence

half-angle

of nozzle

exit cone,

figs. 36, 38, and 49

fig. 42

divergence half-angle cone measured near

fig. 42

of a contoured exit the exit cone lip, deg

equivalent nozzle half-angle from the injection point to the exit plane, determined as the angle between nozzle centerline and a the injection

deg; for a conical angle,

point

nozzle,

to the exit

joint,

the angle between

the nozzle

rim,

fig. 12 eqs. (9) and (10)

deg fig. 12 and eqs. O),

inner and outer joint angles defining flexible joint geometry, deg shear

eq. (I4)

Otinj = ot

centerline and a line from the geometric pivot point to the middle of the flexible

strain

quadruple-lap A

deg

divergence half-angle of a contoured exit cone measured near the nozzle throat, deg

joint

and 42

in. (cm)

line from

3'

figs. 35 - 39

center-

incremental

in elastomer shear change

166

measured

(2), (4), (9), and (10) in

sec. 2.1.7

test in a quantity

eq. (14)

Definition

Symbol

X

angle between

Appears

the nozzle

centerline

line from an injection port side exit-plane rim, deg e

nozzle

expansion

of exit plane

ratio,

and a

In

fig. 49

to the opposite-

defined

area to throat

figs. 25,35,38,39, 40,42,43, and 48

as ratio

area

/

e inj

expansion

ratio

of the nozzle

exit cone

at

the plane of the injection ports, defined as the ratio of the area at this plane to the throat area 0

(1)

angle between motor centerline and centerline of nozzle when nozzle is rotated

(2)

P

about

density,

lbm/ft

fig. 13;eqs.(1),(2), (6),and

and

figs. 35,36,38,39, 42, and 49;eq.(14) eq. (13)

applied

motor

pressure

eqs. (3) and (4)

configuration

compressive hoop stress in reinforcements due to motor pressure, psi (N/m 2)

eqs. (9) and (10)

resultant compressive hoop stress forcements due to motor pressure nozzle vectoring, psi (N/m 2)

eq. (1 1)

in reinand

o_

compressive hoop stress due to nozzle vectoring,

in reinforcements psi (N/m 2)

eqs. (10)

7"

shear

as measured

sec. 2.1.7

stress

in elastomer

quadruple-lap

re

rr

shear

shear

psi (N/m 2)

resultant

shear

shear

stress

vectoring,

due to motor

stress in elastomer and nozzle

in elastomer psi (N/m 2)

167

in

and (11)

test, psi (N/m 2)

stress in elastomer

pressure,

motor pressure (N/m 2) rv

(10)

point,

3 (kg/m a)

relating

and flexible-joint

O" r

pivot

deg angle between motor centerline deflected thrust vector

parameter

Op

the effective

figs. 36,40,43, and 48

eqs. (7) and (8)

due to

vectoring,

due to nozzle

eq. (8)

psi

eqs. (6)and

(8)

Symbol

Definition

(1) (2)

Appears

flexible-joint cone angle, deg discharge angle of the injectant relative to the nozzle centerline,

Rp 2"4 cos

_2 :

3283

eq. (12)

fl

:

eqs. (9) and (10)

tr 3 + tr COS2 /3{Rp 2 (f12 -

/31) 2 - 3283

tr 2}

Identification

205,305,

220,231,and

608

trade

names

of Hughson

name

fiber

(polyethylene

DC 1255

trade

designation

elastomer

polymeric its length

: ERL 2256

of

E. I. du Pont

FM4030-190

material

:

44125

and

trade

of Fiberite

trade

designation

adhesive

epoxy

trade

molding

E. I. du Pont

designation

compound 20-WS-45).

Inc. for a polyester

(now

168

of General available

for silicone

can be stretched

to twice

length

terpolymer

Corp.

Carbide

Corp.

rubber

to its original

diene

Carbide

for bisphenol-A

Corp.

for

for phenolic

epoxy

epoxy

resin

resin

viscosity

impregnated

chopped

material

of FMC Corp.

of

& Co.,

temperature quickly

propylene

of Union

designation

Corp.

at room return

trade designation modifier

trade name fluorocarbons

Freon

that

for ethylene

S-glass compression FMC 47

de Nemours

of Dow Corning

trade designation of Union with viscosity modifier

:,_ERR4205

Co. for primer

terephthalate)

and on release

abbreviation

EPDM

Chemical

systems trade

Dacron

GTR

38,39,40,42,48, and 49

and the side

Material

Chemlok

fig. 12 and eq.(4) figs. 23,35,36,37,

jet deg

angle between side force resultant force vector of the ith injector

1

In

for epoxy

resin system

de Nemours

Tire only

and from

& Co.,

Rubber B.

F.

Co.

Inc.

for

a series

for natural

Goodrich

Co.

of

rubber as BFG

Material

Identification

f

GTR V-45

trade designation butadiene/acrylonitrile

of

General Tire and Rubber compound (now produced

Co. for silica-filled by HiU-Gard Rubber

Co.) trade

Hypalon

name

of

E.

chlorosulphonated IRFNA

inhibited

K1255

trade

LOX

liquid

oxygen,

MHF-3

mixed

hydrazine

Neoprene CN _ _ and Neoprene W

trade

red fuming

designation

name

synthetic

1-1 copolymer

nitroso

AFE-110

carboxy-nitroso Laboratory now

rubber

:_: S-glass

_':: S-901

rubber

acid, propellant

grade

grade

Corp.

&

Co.,

Inc.

for

per MIL-P-7254

for silicone

rubber

per MIL-P-25508

de Nemours

& Co., Inc. for general

of trifluoronitrosomethane polymer

purpose

developed

a butyl

by

rubber

by Parker-Hannifin high-energy

high-strength

and tetrafluoroethylene the

Air

Force

Materials

OH)

B-591-80;

an elastomer, either the hevea brasiliensis

trade

Nemours

(polychloroprene)

kerosene-base MIL-P-25576

Fiberglas

de

synthetic

fuel

(WPAFB,

Parker

Pont

Carbide

propellant

manufactured RP-1

nitric

of E. I. du Pont

rubber

B-591-8

du

of Union

rubber

nitroso

Parker

I.

polyethylene

used

for

O-rings;

Corporation

hydrocarbon

a synthetic tree

compound

fuel,

or a natural

MgO-A1203-SiO2

glass

propellant

compound

developed

by

grade

obtained

per

from

Owens-Coming

Corp.

designation

of

Owens-Corning

with aging surface

finish

S-904

trade designation non-aging surface

of Owens-Coming finish

$34/901

trade

of Owens-Corning

designation

glass fiber cloth

169

Fiberglas

Corp.

for S-glass fiber

Fiberglas

Corp.

for

Fiberglas

Corp.

S-glass

for woven

fiber

S-901

Identification

Material

TCC TR 3005

trade designation of Thiokol Corp. for natural

Teflon

trade

name of E. I. du Pont de Nemours

tetrafluoroethylene Thiokol

ST

Tonox 6040

rubber formulation

& Co., Inc. for a series of

polymers

trade name of Thiokol Corp. for polysulfide trade name of Uniroyal, Inc. for a blend curing agent for epoxy and urethane

elastomer of aromatic amines used as a

resins

_

Tygon ST

trade name of U. S. Stoneware

Co. for polyvinyl

UDMH

unsymmetrical

Viton A

trade name of E. I. du Pont de Nemours & Co., Inc. for a copolymer vinylidene fluoride and hexafluoropropylene

17_PH

semi-austenitic

301 304 347

designations

410

martensitic

2024

wrought

4130 4340

high-strengtl_

6061-T6

wrought aluminum temper T-6

alloy with Mg and Si as principal

7075-T6

wrought T-6

alloy with Zn as principal

dimethylhydrazine,

precipitation-hardening for austenitic

chromium aluminum

170

grade per MIL-P-25604 of

stainless steel

nickel-chromium

steels

steel

alloy with Cu as principal

martensite-hardening

aluminum

propellant

chloride

alloying element

low-alloy steels

alloying elements,

alloying element, temper

ABBREVIATIONS Identification

Organization

ABL

Allegany

ABMA

Army

AEDC

Arnold.Engineering

AFRPL

Air Force

Rocket

AIAA

American

Institute

BOWACA

Bureau

CPIA

Chemical

DAC

Douglas

ICRPG

Interagency

JANAF

Joint

Army-Navy-Air

JANNAF

Joint

Army-Navy-NASA-Air

JANAF-ARPA-NASA

Joint

Ballistics

Ballistic

Laboratory

Missile

Agency

Development Propulsion

Center

Laboratory

of Aeronautics

of Weapons

Advisory

Propulsion Aircraft

and Astronautics

Committee

Information

Agency

Company

Chemical

Rocket

Propulsion

Force Force-Advanced

National

Aeronautics

LMSC

Lockheed

Missiles

and Space

Company

LMSD

Lockheed

Missiles

and Space

Division

LPC

Lockheed

Propulsion

NAVORD

Naval Ordnance

Command

NOTS

Naval Ordnance

Test

SAE

Society

and Space

UTC

United

WPAFB

Wright-Patterson

of Automotive

Company

Station Engineers Center

Air Force

171

Group

Force

Army-Navy-Air

Technology

for Aeroballistics

Base

Research

Administration

Project

Agency-

REFERENCES 1.

Anon.:

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Amick, Located

4.

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6.

7.

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Podell,

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Fuller,

12.

13.

14.

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Interactions TDR-63-22

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Vector

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Space

Vehicle.

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Space

Vehicle.

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16th

JANAF

Solid

1964.

System.

1960,

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Div.,

J. E.; and Murray, J. A.: Integral Rocket Ramjet Booster System Demonstration (U). DCN-N-37-23, Annual

Exploratory Development (CONFIDENTIAL)

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Program, Div.,

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'and

Chemical

Motor Demonstration Chemical Corp./Wasatch

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24. Miltenberger,

Thiokol

100-Inch Thiokol

an Elastomeric Seal Lockheed Propulsion

Fabrication

of Large Solid

Anon.: Final Nozzle for Corp./Wasatch

TWR-2486,

R.:

(AD-502027L),

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and

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C3 Joint Venture July 1967.

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source material

28. White,T. C.:ThrustVectorControl- Elastocomposite Joint(U).DCN-N-17-6, AnnualExploratory Research Report- 1971,Vol.2, Hercules Inc./ABL,February1972,pp. 1-68.(CONFIDENTIAL) 29.Miltenberger,L. E.: Elastocomposite Joint-Thrust Vector Control (U). DCN-N-26-2, Annual Research andExploratoryDevelopment Report- 1972,Vol.2. Hercules Inc./ABL,December 1972, pp. 119-202. (CONFIDENTIAL) 30. Hurley,L. H.; and Kimmel,N. A.: Applicationof ControllableSolidsin ReentryMeasurements Program (U).Rep.TR-0059($6816-89)-1, Aerospace Corp.,Aug.31,1970.(CONFIDENTIAL) 31. Bertocci,R. P.: The Nike-ZeusPropulsionandJetheadControl Systems(U). Bulletinof 18th JANAF-ARPA-NASA SolidPropellant Group,Vol. 1 (AD-330129), CPIA,June1962,pp.161-179. (CONFIDENTIAL) 32. Kirchner,W. R.: Development of Advanced PolarisFirst StagePropulsionSystem(U). Bulletinof 18thJANAF-ARPA-NASA SolidPropellant Group,Vol. 1 (AD-330129), CPIA,June1962,pp.3-27. (CONFIDENTIAL) 33. Ellis,R. A.: Development of a Carbon-Carbon Nozzlefor the TridentI (C4)ThirdStageMotor(U). CPIAPubl.242,Vol. I, CPIA,November 1973,pp.89-115. 34.

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1965.

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N,

(AD-371800), 41.

Waldeck, Rep.

Diameter

AD-365662,

August

Final

(AD-376999), 40.

Report,

Thiokol A.;

June

Submerged

Chemical

Slegers, Air Force

L.;

1962,

pp.

and

and

Thrasher,

R. V.; Deslauriers, Corp.,

113-122. Program.

Nozzle

I.:

AFRPL-TR-65-4 Thiokol

Development,

Div., June D.

JANAF-ARPA-NASA

Air Force

E. J.; and McVey,

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175

D.C.),

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(5 vols:

AD-365660,

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Div.,

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D. BSD-TR-66-31/C

1966.

Gimballed

(Edwards

Solid

(CONFIDENTIAL)

AD470452),

Gimbal

Command,

of 18th

Nozzle

Corp./Wasatch

Systems

Pneumodynamics

Bulletin

Movable

AD-365663,

G. H.; Hensley,

6602-1,

System.

I (AD-330129),

AD-365661,

39.

Skybolt

Integral

Nozzle.

Base, CA),

F. D.: Flexible

September

1959.

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December Skirt

1965. Nozzle

(CONFIDENTIAL)

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Skirt

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Program

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1960.

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43.

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:,

1960. 44.

G. H.:

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Rocketdyne

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Div., G. H.:

.., _./._.: k(AD7373908), 46.

6602-k,

(CONFIDENTIAL)

Spann,

• : .

Rains,

Grain

North An

D. A.: Solid Solid

Advanced

American

Nozzle

1966,

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Omnivector

CPIA , June

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Chemical

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1968.

Phase II Design Compliance Report, Fleet Ballistic Chemical Corp., Mar. 16, 1971. (CONFIDENTIAL)

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OD

\

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1971.

Anon.:

*99.

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*101.

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Command,

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1969.

44125,

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• 102. _ Anon.:

104.

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Natural

Lockheed

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Systems

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Natural

Ordnance

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October

Spaid,

ARS

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A.:

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Methods

for

the

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1967.

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of

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Sizes

in Liquid

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1968.

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Vector

and Second

Lockheed

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Aspects

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Jets

Atomized

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in Low

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Stress

Technology

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(U). LMSC 804506,

Lockheed *110.

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Streams

Zeamer,

Report "109.

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of

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1961.

1964.

Effectiveness

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Vector

Control

Data

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800877,

(CONFIDENTIAL)

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May 1961,

Secondary

and Space

Vector

Co., August

CA),

Stage

Missiles

(U).

July

Rep.

1961,

Final

Nos.

R-l,

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R-2, 1961. III).

and R-3

of P-27,

Dynamic

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United

10, 1969.

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*120._

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"121.

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• 122.

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123.

"124.

and

Water

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C. A.: Determination CR-72792, DeCember

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Aerojet

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LMSC

BSD-TR-66-93,

Subcontract

for

the

of Liquid

Surveyor

Thrust

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"126.

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on TVC

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on Nozzle

Memo,

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(U). TM 53-42-4,

"125.

Parameters 1965.

Vernier

Interoffice

Panel

LMSC 803311,

Vector

R. G.: Preliminary Results of P-29 Fluid Injection Lockheed Missile s and Space cO., November 196i.

Effect of Some Nozzle and TVC Hercules Inc./Magna, September

18-10703,

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Perchlorate.

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United

IDC 52-30, Lockheed ' .... '_ ' _ ....

Membranes.

Bladders

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181

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Report.

_

114.

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source material

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R.

L.:

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and Space

Anon.: Weapons GM-TR-0165-00478, Anon.:

Item

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Co., May

Thrust

System 133B, Aerojet-General

Detailed A6658,

Second Corp.,

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6, 1972.

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Anon.: 156-5.

134.

Charwat, A. F.; Roos, J. N.; Dewey, F. C.; Flows - Part I - The Pressure Field. J. Aerospace

135.

Charwat, Flows-

F.; II-

Rep.

IDC-57-11-59,

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(Titan

III

Wing VI Motor Data 1969. (CONFIDENTIAL).

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Solid

Book

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Model

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Technology

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(U).

SR-73-AJ-I

(CONFIDENTIAL)

Anon.: TVC System December 1970.

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P-10.

Stage/Minuteman Revised March 21,

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Test

1961.

C/D).

UTC

4404-70-330,

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Final 1966.

Center,

Results,

Motor

and Hitz, J. A.: An Investigation of Separated Sci., vol. 28, no. 6, June 1961, pp. 457-470.

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pp. 513-527. "136.

Zeamer,

R. J.:

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138. "139.

140.

Anon.:

156-Inch

October

1965.

Anon.:

Hibex.

McQueen, Inc./ABL,

142.

Injection

Fiberglass

Rep.

Thrust

Inc./ABL,

LITVC

D2-99600-1

Vector

August

Control,

Starrett,

D.: Final

Report

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(AD-371266L),

Co., October

Anon.:

Polaris

Space

Co., March

- Sprint

Fluid

1964. Injection

Missile

Distribution

of Loads

Due

to Vectoring.

1963. AFRPL-TR-65-192,

The Boeing

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and Space 141.

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Operation

Control

Study

Co., March Report

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Thiokol

Chemical

Corp.,

1966.

(U). Rep.

LMSC

ZM-656-401D,

665480,

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Missiles

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Vector

:Control.

Rep.

LMSC

800550,

Lockheed

Missiles

and

1961.

Speisman, C.; and Kallis, 63-1942.27-28, Aerospace

J.: Preliminary Results, Corp., (San Bernadino,

Quadrant Interaction CA), June 3, 1963.

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Unpublished.

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143. Hair,L. M.; andBaumgartner, A. T.: An EmpiricalPerformance Modelof Secondary Injection Thrust Vector Control (CONFIDENTIAL) "144. ! Green, August 145.

146.

C. J.i Desired 1960.

Green, C. Preliminary Walker,

R. E.; and

Rep.

Properties

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(U).

of the

4-64-014,

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Injectant.

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Missiles

4511-196,

and

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Test

Shandor,

M.: Influence

64-112,

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AIAA

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148.

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149.

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152.

Obert,

153.

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154.

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155.

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156,

Anon.: Valves.

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157.

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D. K.; and Lipow,

Scaling

of Injectant

Solid

147.

Effects.

Procedures

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of Cost

M.: Reliability:

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4511-195,

Analysis.

Management,

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for Fluid

U.S.

Naval

Thrust

(Palo

Alto,

Ordnance

RM-3589-PR

for Launch

Methods

Injection

Conference

Station,

(AD

Vehicles

of Thermodynamics.

McGraw-Hill Expulsion

Internal

Tank

Book

Co. (New

Performance.

UTC

Ballistics.

Components.

York),

Station,

411554),

RAND

Prentice-Hall,

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Criteria

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Criteria

Prediction.

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Solid

1960.

Relief Valves, Check •Valves, Burst Disks, Monograph, NASA SP-8080, March 1973. and

Jan.

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and Mathematics.

Vector

CA),

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for 1964.

of Additives on Propellant Performance and Motor Operating Conditions. Report 1DP1210, U. S. Naval Ordnance Test Station, December 1960.

No.

Secondary 1960.

LMSC

NASA

Unpublished.

Space

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and Explosive

Vehicle

Design

source material

FirstStageMotor. "158. Anon.:StructuralandThermalAnalysisFinalReport,Poseidon Data

Item

October

159. Heaton,

No. SEO25-A2A00HTJ,

Rep.

1, Hercules

Inc./Thiokol

Chemical

Corp.

Vol. III - Nozzle. (A Joint Venture),

1970. H.

(AD-510749),

S.; and

Daines,

Hercules

W. L.: Flow

Inc./Magna,

Field

September

Analysis 1970.

of Rocket

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184

Motors

(U).

AFRPL-TR-70-98

(CONFIDENTIAL)

Unpublished.

Collected

source

material

NASA SPACE VEHICLE DESIGN CRITERIA MONOGRAPHS ISSUED TO DATE

ENVIRONMENT SP-8005

Solar

SP-8010

Models

of Mars Atmosphere

SP-8011

Models

of Venus

SP-8013

Electromagnetic

Radiation,

SP-8017

Magnetic

SP-8020

Mars Surface

SP-8021

Models

SP-8023

Lunar

SP-8037

Assessment

SP-8038

Meteoroid Environment October 1970

SP-8049

The Earth's

SP-8067

Earth

SP-8069

The Planet

SP-8084

Surface Revised

SP-8085

The Planet

Mercury

SP-8091

The Planet

Saturn

SP-8092

Assessment June 1972

and

(1968),

Models,

(90

March

(1970),

to

Lunar

March

1969

km),

Revised

Surface),

to 2500

March

1973

Magnetic

(1970),

(Interplanetary

Radiation,

July

December

1971

(1971),

(Launch

March June of

Fields,

September and

1970

Planetary),

1971

Extremes

Control

Earth

1972

1969

Model-1970

and Emitted

185

(Near

of Spacecraft

Ionosphere,

Atmospheric June 1974

September

May 1969

and Control

Jupiter

Revised

May

Atmosphere

1971

1968

and Extraterrestrial,

Models

of Earth's

May

May

Model-1969

Fields-Earth

Albedo

(1967),

Atmosphere(1972),

Meteoroid Environment March 1969

Surface

Revised

1971

and

Transportation

Areas),

1972

1972

Spacecraft

Electromagnetic

Interference,

SP-8103

ThePlanets Uranus, Neptune,andPluto(1971),November 1972

SP-8105

Spacecraft ThermalControl,May1973

SP-8111

Assessment andControlof Electrostatic Charges, May1974

STRUCTURES SP-8001

BuffetingDuringAtmospheric Ascent,Revised November 1970

SP-8002

Flight-Loads Measurements DuringLaunchandExit, December 1964

SP-8003

Flutter,Buzz,andDivergence, July 1964

SP-8004

PanelFlutter,Revised June1972

SP-8006

LocalSteadyAerodynamic LoadsDuringLaunchandExit, May 1965

SP-8007

Bucklingof Thin-Walled CircularCylinders, Revised August1968

SP-8008

Prelaunch GroundWindLoads,November 1965

SP-8009

Propellant SloshLoads,August1968

SP-8012

NaturalVibrationModalAnalysis,September 1968

SP-8014

EntryThermal Protection,August1968

SP-8019

Bucklingof Thin-Walled Truncated Cones,September 1968

SP-8022

Staging Loads,February1969

SP-8029

Aerodynamic andRocket-Exhaust HeatingDuringLaunchandAscent May1969

SP-8030

Transient LoadsFromThrustExcitation,February1969

SP-8031

SloshSuppression, May1969

SP-8032

Bucklingof Thin-Walled DoublyCurvedShells,August1969

SP-8035

WindLoadsDuringAscent,June1970

SP-8040

FractureControlof MetallicPressure Vessels, May1970

SP-8042

MeteoroidDamage Assessment, May1970

186

SP-8043

Design-Development Testing,May1970

SP_044

Qualification Testing, May1970

SP-8045

Acceptance Testing,April 1970

SP-8046

LandingImpactAttenuationfor Non-Surface-Planing Landers,April 1970

SP-8050

StructuralVibrationPrediction, June1970

SP-8053

NuclearandSpace RadiationEffectsonMaterials, June1970

SP-8054

Space RadiationProtection, June1970

SP-8055

Prevention of CoupledStructure-Propulsion Instability(Pogo),October 1970

SP-8056

FlightSeparation Mechanisms, October1970

SP-8057

StructuralDesignCriteriaApplicable to a Space Shuttle,Revised March 1972

SP-8060

Compartment Venting,November 1970

SP-8061

Interactionwith Umbilicals andLaunchStand,August1970

SP-8062

EntryGasdynamic Heating,January1971

SP-8063

Lubrication,Friction,andWear,June1971

SP-8066

Deployable Aerodynamic Deceleration Systems, June1971

SP-8068

BucklingStrengthof StructuralPlates,June1971

SP-8072

AcousticLoadsGenerated by thePropulsion System, June1971

SP-8077

Transportation andHandlingLoads,September 1971

SP-8079

StructuralInteraction with ControlSystems, November 1971

SP-8082

Stress-Corrosion Cracking in Metals,August1971

SP-8083 SP-8095

" DiscontinuityStresses in MetallicPressure Vessels, November 1971 PreliminaryCriteria for the FractureControl of SpaceShuttle Structures, June1971

187

SP-8099

Combining AscentLoads,May1972

_...

SP-8104

Struc, tural InteractionWith Transportationand Hand!ingSystems, January1973

GUIDANCE ANDCONTROL SP-8015

Guidance andNavigation for EntryVehicles,November 1968 "

SP-8016

Effectsof StructuralFlexibilityon Spacecraft Control

Systems,:

April

1969

SP-8018

Spacecraft

Magnetic

SP-8024

Spacecraft

Gravitational

SP-8026

Spacecraft

Star

SP-8027

Spacecraft

Radiation

SP-8028

Entry

SP-8033

Spacecraft

Earth

SP-8034

Spacecraft

Mass Expulsion

SP-8036

Effects

Vehicle

Torques,

Torques,

Trackers,

July

Control,

May 1969

October

November

Horizon

1969

1970

Torques,

of Structural

February

March

1969

1969

Sensors,

December

Torques,

Flexibility

1969

December

1969

Launch

Vehicle

on

Control

Systems,

1970

SP-8047

Spacecraft

Sun Sensors,

SP-8058

Spacecraft

Aerodynamic

SP-8059

Spacecraft 1971

SP-8065

Tubular

SP-8070

Spaceborne

Attitude

June

Torques, Control

Spacecraft

Booms

Digital

1970 January

During

(Extendible,

Computer

Systems,

1971

Thrusting

_ Maneuvers,

Reel

Stored),

March

1971

" _:, February

February

1971

i

SP-8071

Passive

SP-8074

Spacecraft

SP-8078

Spaceborne

Gravity-Gradient Solar

Libration

Cell Arrays,

Electronic

188

May

Imaging

Dampers,

February

1971

Systems,

June

197!

1971

SP-8086

Space

Vehicle

Displays

SP-8096

Space

Vehicle

Gyroscope

SP-8098

Effects of June 1972

SP-8102

Space

CHEMICAL

Design

Structural

Vehicle

Criteria,

Sensor

1972

Applications,

Flexibility

Aceelerometer

March

on

October

Entry

Applications,

Vehicle

1972 Control

December

Systems,

1972

PROPULSION

SP-8087

Liquid

Rocket

Engine

SP-8113

Liquid 1974

Rocket

SP-8107

Turbopump

SP-8109

Liquid

Rocket

SP-8052

Liquid

Rocket

Engine

Turbopump

SP-8110

Liquid

Rocket

Engine

Turbines,

SP-8081

Liquid

Propellant

SP-8048

Liquid

Rocket

SP-8101

Liquid 1972

SP-8100

Liquid

Rocket

Engine

SP-8088

Liquid

Rocket

Metal

SP-8094

Liquid

Rocket

Valve Components,

SP-8097

Liquid

Rocket

Valve

SP-8090

Liquid

Rocket

Actuators

SP-8080

Liquid Rocket Pressure Regulators, Disks, and Explosive Valves, March

Engine

Systems

Rocket

Fluid-Cooled Combustion

for Liquid

Engine

January

Turbopump

Engine

189

Turbopump Tanks

1974 December

1973

1972 March

Shafts

Gears,

and

March

1971 Couplings,

September

1974

Components,

August

May

1974

1973

Assemblies,November and Operators,

November

May 1971

Bearings,

and Tank

1972

1974

March

Turbopump

August

Turbopumps,

Inducers,

April

Devices,

Engines,

Flow

Gas Generators,

Chambers,

Stabilization

Rocket

Centrifugal

Engine

Combustion

.1973 May 1973

Relief 1973

Valves,

Check

Valves,

Burst

SP-8064

SolidPropellant Selection andCharacterization, June1971

SP-8075

SolidPropellantProcessing Factorsin RocketMotorDesign,October 1971

SP-8076

SolidPropellant GrainDesign andInternalBallistics, March1972

SP-8073

SolidPropellant GrainStructuralIntegrityAnalysis, June1973

SP-8039

SolidRocketMotorPerformance AnalysisandPrediction,May1971

SP-8051

SolidRocketMotorIgniters,March1971

SP-8025

SolidRocketMotorMetalCases, April 1970

SP-8041

Captive-Fired Testingof SolidRocketMotors,March1971

190 *U.S.

GOVERNMENT

PRINTING

OFFICE:

1975

-

635-275/53

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