Maxwell St 1

TAILORED FORCE FIELDS FOR SPACE-BASED CONSTRUCTION: KEY TO A SPACE-BASED ECONOMY Narayanan Komerath, Sam Wanis, Joseph Czechowski, Bala Ganesh, Waqar Zaidi, Joshua Hardy, Priya Gopalakrishnan School of Aerospace Engineering, Georgia Institute of Technology

Source: www.nasa.gov School of Aerospace Engineering, Georgia Institute of Technology

OUTLINE 1.

Forces on objects in steady and unsteady potential fields

2.

Generalization: Optical and other E-Mag fields; and acoustic fields

3.

Application Horizons

4.

Near term: Acoustic Shaping: results & applications

5.

Far Horizon: Electromagnetic force fields

6.

Middle Term – Magnetic Fields to demonstrate a particular solution -Sample Problem : the O’Neill Habitat - Architecture

7.

Costing Using a Space-Based Economy Approach

Source: www.nasa.gov School of Aerospace Engineering, Georgia Institute of Technology

INTRODUCTION In space, minor forces exerted over long periods can achieve major results. Generation of forces by interaction with steady potential fields is well-known ESL: NASA MSFC/ LORAL

NASA .

M2P2: NASA / U. Wash.

Solar Sail: NASA

Here we consider: 1.

Radiation Force due to unsteady interactions between beamed energy and matter – near & far term applications.

2.

Quasi-steady magnetic fields: middle term architecture to get to the far horizon .

Laser/ Microwave Sail: JPL

Relevance: automatic construction of large/complex objects from random-shaped materials.

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FORCES IN UNSTEADY POTENTIAL FIELDS 1. Radiation Force Due to Beamed Energy Radiation pressure due to plane wave on surface = k*E. ( E = Energy density) Absorbing surface: k =1. Reflective surface: k=2. Gradient forces: Beam waist acts as particle trap for transmitting particles, due to intensity gradient. Optical Tweezers: Particles are forced to the focus / waist of a CW laser beam -interpreted using geometric optics and refractive index for particles >> λ. -also works using Mie theory where particle size ~ λ -recently found to work for Rayleigh regime – nanoparticles << λ Satellite Positioning: Lapointe, NIAC study 2001.

Ultrasonic beams “Fingers of Sound / Space Drums” Used to hold and manipulate levitated/ suspended particles. R. Oeftering, NASA

Radiation pressure on objects due to coherent beams is used in optics and acoustics. School of Aerospace Engineering, Georgia Institute of Technology

FORCES IN UNSTEADY POTENTIAL FIELDS 2. STANDING WAVE FIELDS: Particles Drift into Stable “Traps”. •For particle size << λ, standing wave trap force ~ 103 times the single-beam force. •Trap stiffness in standing wave trap ~ 107 times the single-beam trapping stiffness. D ( z)

2

1

0

•Source only needs to provide small gain over losses -

1

2

0.02

0.04

Force

0.06

Potential z

Trap regions can be of complex shape: Pressure distribution for a higherorder mode in a rectangular acoustic resonator.

Stable Trap

With standing waves in a low-loss resonator, small input intensity suffices to produce substantial forces on particles. Various mode shapes can be generated by varying frequency and resonator geometry. School of Aerospace Engineering, Georgia Institute of Technology

Acoustic Electromagnetic General

CONSERVATION EQUATIONS ∂ (density of quantity ) + ∇ • ( flux of quantity ) = sources − sin ks ∂t

∂ ∂t

1  ε o E 2

2

1 B2 + 2 µo

Electromagnetic energy density

 E×B  + ∇ •    µo Poynting flux

  = − ( J • E )  work done on Particles by EM field

( )

1 ∂  1 p2 2   + ∇ • ( pu ) = X • ∇ p  u + ρ o 2 2 ∂t  2 ρ o c  Acoustical potential Energy density, ep

Acoustical kinetic Energy density, ek

Acoustic Intensity flux, I

Work done on Particles by acoustic field

ep =

potential energy that can be stored in the fluid by compressing it

ek =

kinetic energy due to acoustically energized fluid

I= rate at which work is being done by unit area of fluid supporting an externally induced normal stress p and moving with velocity u is pu, i.e. rate (and direction) at which acoustic energy crosses unit area of space School of Aerospace Engineering, Georgia Institute of Technology

IMPORTANT PARAMETERS & ORDERS OF MAGNITUDE Optics

Acoustics z

z

Maxwell’s stress tensor Rayleigh regime diameters: nanometers Mie regime: microns

z

Refractive Index

z

z

Optical intensity From Zemanek (1998): 514.5 nm laser in water; beam waist of 8 wavelengths; glass sphere of radius 5nm; refractive index 1.51; Force = 2.5 *10-22 N.

z

z z

z

z z

z

Radiation stress tensor Rayleigh regime diameters: millimeters to centimeters Mie regime: meters Particle density vs. density of acoustic medium Sound intensity Wanis[1999]: GT acoustic chamber, 156 dB at 800 Hz (1 0 0) mode at 2mm radius rigid particles Force = 3.3 micro-newtons

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Tailored Force Fields (TFF): Time Line / Size / Application Map 1 – 5yrs ULTRASONIC

10-6m

10-3m

5-20 yrs STANDING WAVE ACOUSTCS

20-30yrs STEADY MAGNETIC TELEPRESENCE

STEADY BEAM ACOUSTICS

30- 50 yrs.

LONG-WAVE ELECTROMAGNETIC

FORMATION FLIGHT ISS PARTS

100m

HEAT SHIELDS : HABITAT PARTS/ FUEL TANKS

103m

HABITAT CONSTRUCTION

ASTEROID

105m

RECONSTRUCTION School of Aerospace Engineering, Georgia Institute of Technology

ACOUSTIC RADIATION FORCE: PRIOR APPLICATIONS •Rayleigh – proposed expression for radiation pressure in acoustic fields, analogous to Maxwell’s stress tensor. •King 1934: Theory for radiation force in acoustic fields – formation of dust striations in water tanks. Forces considered to be insignificant except with ultrasonic frequencies and neutrally-buoyant particles in water. •Levitation experiments: Ultrasonic levitators used to lift steel spheres – to demonstrate utility in non-contact melting and positioning within furnaces. •STS experiments: Holding molten drop of metal inside a container in micro-gravity. Problem: Radiation force lost when phase change / cooling occurred. Attributed to reversal of force due to formation of envelope of heated gas around the sphere. [Wang 1998] •Liquid manipulation using ultrasonics: NASA Glenn research •NASA Hybrid electrostatic levitator / ultrasonic manipulator facility.

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ACOUSTIC SHAPING •GT extension: Extended the idea of positioning a single droplet, to the formation of entire walls in a chamber. Question: would particles migrate to point of minimum potential, or remain along entire surfaces of low potential? •KC-135 tests. Flight test proof that entire walls would be formed. Self-alignment seen. No particle spin.

Acoustic chamber

Ground test comparison between predicted pressure contours and measured wall locations

Mode 110 Styrofoam walls formed in reduced gravity School of Aerospace Engineering, Georgia Institute of Technology

ACOUSTIC SHAPING Wall formation process: KC-135 test. Frequency 800 Hz

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SIMULATION: PREDICTED WALL SHAPES

220

110

100+020

320

230+100

110+220

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FAR HORIZON: ASTEROID RECONSTRUCTION? •Solar-powered radio resonators in the NEA region to reconstitute pulverized asteroids into specified shapes. •Formation-flown spacecraft to form desired resonator geometry. •Asteroids pulverized using directed beam energy or robots, •Solar energy converted to the appropriate frequencies. •Materials and structures for such an endeavor must come mostly from lunar or asteroidal sources. Example Point: Particle diameter: 0.1m Wavelength: 2m Particle acceleration: 10-5 g Resonator intensity: 170 MW/m2 Resonator Q-factor: 10,000 Active field time: 13 hrs Beam diameter = 100m Collector efficiency: 10% Collector area w/o storage: 1 sq.km

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Can we generate radio waves intense enough?

z

z z z

In 1974, the Arecibo observatory transmitted a message into outer space Power of transmission was 20 trillion watts Courtesy of the NAIC - Arecibo Observatory, a facility of the NSF. Frequency 2380 MHz. David Parker / Science Photo Library Wavelength of ~12.6 cm Signal duration: 169 seconds

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Space Based Economy Self-sustaining Economy Support/Service Economy

Time

Space Habitats Lunar Manufacturing

Lunar Mining

Lunar Power

Lunar Launcher Lunar Resources GEO Station Maintenance Com-sats

Space Station Research

Orbit transfer vehicles Robotics

Fuel

Exploration

Military

Repair Sensing

GPS

Earth Launch

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Middle Term Test Case for Costing: ELECTROMAGNETIC CONSTRUCTION OF A 2KM DIAMETER, 2KM LONG RADIATION SHIELD At the 10-30 year horizon, force field tailoring can be used to build the first large human habitat at a Lagrangian point of the Earth-Moon system. Gerard O’Neill proposed such habitats and explored their construction in the 1970s.

Features of the O’Neill [1975] habitat concepts: •Economic opportunities as motivator •Moon as first source for extraterrestrial resources, •L5 as the logical location for the settlement. • “Bernal sphere” + toroidal agriculture stations on either side. Near 1-g at equator •Shell made of aluminum and glass (to admit sunlight ) •Support structure made of aluminum ribs and/or steel cable •Projected earth-LEO launch costs of $110/lb •Lunar-based mass driver to send much of the required mass into Space

Radiation shielding dominated mass of the settlement. School of Aerospace Engineering, Georgia Institute of Technology

PRESENT APPROACH TO BUILDING HABITAT #

1975 models

Present model using Tailored Force Fields (TFF)

1

$110/ lb Earth- LEO

$1,300 - $14,000 per lb to LEO

2

Human labor on-site for all construction.

Robotic with Earth-based telepresence supervision

3

Construction at L-5

Shell construction at L-2 followed by slow move to L-5

4

Lunar mass driver gas-powered; H2 from Earth.

Lunar-equatorial Solar-power fields . 20 launchers; round-the clock launches;

5

Baseball-size loads. High Isp. 30g; 10km run

Railcar-sized loads. 8-g, 40km track.

6

Entire interior pressurized for “shirtsleeves” comfort.

10 to 30 meters at rim pressurized, 30-meter bubbles for micro-climates.

7

Machinery required to make panels etc.

Solar-heated powder sintering & furnaces, robotic manufacturing on the Moon.

Such a project becomes feasible as the centerpiece of a coherent plan for a Space-based economy of the future.

School of Aerospace Engineering, Georgia Institute of Technology

Shield Construction: 1 •Structural strength comes from a Grid of cables made on the Moon and deployed in orbit at EarthMoon L-2. Rings of 12.5mm dia. cable segments, 1km in radius, spaced 4 meters apart, will be connected by longitudinal cables. • Grid deployment: Cables with attached mini-thrusters are deployed from lunar-launched “box-cars”. First 4 lunar-launched segments

Micro-thrusters separate cable rings and start rotation, Tension kept low until first boxcar ring is complete.

Each regolith-filled “boxcar” is brought by a hybrid gas/ emag “shepherd” craft, and guided towards the grid.

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Shield Construction:2 •Cable Grid is powered by solar panels, with gas thrusters for orbit corrections. Rotation holds the grid in tension during shell construction. •Each arriving load-train is captured by a winched tether attached to the rotating grid. Axial momentum is transferred to radial and tangential momentum, bringing the load to the periphery at 1kmph, into the space between the outer grid and an active, powered electromagnetic “construction grid. •Electromagnetic interaction between the loads, the construction grid, and the shepherds, moves the loads into position against the outer grid. The shepherds leave the grid. •Robots attached to the construction grid complete the attachment of the box-cars.

Ring of boxcars joined to form ribs

Winched tether Captures load: Momentum transfer

E-mag grid

“Spider” Final positioning

Shepherds maneuver boxcars into place using e-mag field

School of Aerospace Engineering, Georgia Institute of Technology

Shield Construction:3 Regolith-laden boxcars being delivered by “Shepherd” The “End Caps”

Thrusters

Assembled boxcars Structural Support

Side Wall Filled with regolith / water

Radial Cables carry grappling tethers & winches.

E-Mag Spider

Inner Active E-Mag Grid

Outer Cable Grid

Legs Gripping Cable

School of Aerospace Engineering, Georgia Institute of Technology

Construction Parameters • Radius = 1km

•Solar Panel area for grid = 350 m2

• Length = 2km

•Boxcar :2m x 2m x 20m

• Shield Depth 2m

•Mass per load: 160,000 kg

• Rotates at 0.945 rpm for 1g

• Regolith sp.gr.= 2

• Grid current = 15 amps

•10 launchers operational at any time (20 total around lunar equator)

• 500 loops of cable; • Cable dia =12.5mm

• Shepherd unit current required: 15 amps • Time to build: 10 yrs.

•Lunar Solar-Power Fields made by robotic rovers around the equator •Lunar metal extraction plants; cable manufacture using robotic plants. •Lunar launcher construction initiated. •Load preparation system developed on the Moon •First cable-set deployment and spin-up. •First ring of loads completed; rigid framework for subsequent cables and loads. •Solar collectors, thrusters; hub system with tethers and “Construction Spiders” attached. •Oxygen / other propellant gas extraction from regolith to supply thrusters. •Cylinder completion; endcap framework sealed with regolith and water-filled bags; Oxygen/Earthshipped N2 atmosphere bubbles for habitation spaces near 1-G rim; micro-g axial facilities. •Human habitation commences. School of Aerospace Engineering, Georgia Institute of Technology

Bootstrapping Infrastructure

Credit: D. Rawlings

School of Aerospace Engineering, Georgia Institute of Technology

Reduction in Public Expenditure Due to Private Industry. zLunar

Power: (Ignatiev et al, NIAC Phase 1, 2000) $0.40/KwH Strip Mining on the Moon (extrapolated from 1979): $ 8 B

z

z

Lunar Launcher System $ 37 B

zMetal

cost for cylinder structure: $40B

zTotal

Cost: $150 B

Development cost of Alaskan oil facilities: $67B, total revenue to-date $267B, incl. $55B Fed. Tax. (revenues from known precious resource) Space Business total annual revenue 2000: $116B (AW&ST, April 2001 revenues from industries & technologies which were created by the new capability NASA Lunar Base construction cost estimate (published): $112B

Lunar Power Generation

100 $B (Y 2000)

Compare with:

80 60 40

Mining

Mass Driver

20 0

10

12

14

16

Years School of Aerospace Engineering, Georgia Institute of Technology

“Competitive Delivered Cost” Approach Cost of Launch Cost from Earth to Moon: $12,000 / kg z Cost of Lunar Launch: $45 /kg in first year reducing to $37/kg by fourth year ( Cost Assessed dictated by the lowest cost from available Earthbased alternatives ) Competitive “Delivered Cost” of Shield: $ 2.5 trillion (!!) z

Using Past Assessments and a Collaborative Space Economy Approach Business plans of Space Businesses patched into the network of a Space based Economy Survival of service providers depends on the survival of limited customer base. The business plan of a single industry that may appear risky when viewed by itself, becomes realistic when patched into the network of a Space based Economy Justin Hausaman 2001

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Summary of Industry & Infrastructure Bootstrapped by Habitat Project 1. Power plant. 2. Metal mining. 3. Flexible manufacturing facilities for cables, metal panels, box cars, rails. 4. LEO – GEO – Lunar Orbit shipping industry 5. Tether system for delivery to the Moon. 6. Electromagnetic rail launchers – nucleus of circumlunar ground transport system. 7. Oxygen extraction plants on the Cylinder and the Moon 8. Solar panel production 9. Repair, exploration and prospecting facilities on the Moon. 10. Habitat sized for eventual population of 10,000 people in orbit. 11. Means to ship construction materials anywhere in the vicinity of Earth

School of Aerospace Engineering, Georgia Institute of Technology

Concluding Remarks z z z z z z z z z z z

z

z

Tailored electromagnetic force fields enable massive automated construction at low recurring cost. Theoretical approaches to acoustic, optical and electromagnetic force fields unified into a common Rayleigh regime prediction capability (Phase 1) Resonators offers large increase in force and trap stability Acoustic shaping proven in flight and ground experiments Optical trapping proven in microscopy. Microwave and radio wave TFF are efficient in solar-power usage for construction Costing using a Space-Based Economy approach illustrated using the middle term radiation shield project. Quasi-steady magnetic fields enable telepresence-controlled construction of the radiation shield for human settlements near Earth. Overall cost becomes practical when lunar- and Space-based industries are included. Unlike exploration-focused government programs and isolated business plans for private ventures, a Space-Based Economy approach can unite public support for Space enterprise. As more business visions are enabled by the assurance of a massive market provided by the infrastructure project, the level of public funding needed comes down, even before tax revenues. Coherent plan needs to be articulated for developing a mutually-supportive network of economically-useful projects, with synergistic markets, risk evaluation and pricing.

Please visit http://www.adl.gatech.edu/research/tff/ School of Aerospace Engineering, Georgia Institute of Technology

BACKGROUND

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TAILORED FORCE FIELDS: CONCEPT In Space, minor forces exerted over long periods can achieve major results. Force fields of various kinds can be used to build large structures. Steady potential fields: Objects Radiation Force Due to Beamed Energy: Coherent beams exert pressure on scattering objects. •Laser propulsion •“Fingers of Sound / Space Drums”

Interact with a steady force field. •Electrostatic Levitation •Magnetic attraction •Electromagnetic sails D( z)

2

1

Standing wave fields: particles accumulate into walls along stable “traps”. “Acoustic Shaping”

Electromagnetic Shaping??

0

1

2

0.02

0.04

0.06 z

•Complex surface shapes can be tailored. • Source only needs to provide small gain over losses -

fR ~ IkR3

•Radiation force in a standing wave field can be > 1000 x that of the source beam. •“Stiffness” of the stable nodes can be 7 orders of magnitude higher than in single-beam. Present Project: Integrate these technologies to show how very large structures can be built for human habitats – in the context of a Space-Based Economy

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Sample Planning Architecture for SBE stakeholders Scope of the Project: Business scenarios, Rationale. Functional View: Role of the Organization in SBE. What will it achieve? Business View: Economic motivation, Costing, Business Drivers, Organization structure/hierarchies

Technology View: Technologies required, Components, Activity areas, R&D.

Deployment: Schedules, Construction plans, Implementation plans

Operations: Detailed procedures, Production plans, Maintenance plans.

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Power

Technology Options Metal Mining & Extraction •Preferred Option:

Preferred Option: •Lunar Solar-Power Fields made by robotic rovers. - 20 power plants around the equator Cost estimate: $0.40 per kilowatt-hr (Ignatiev et al) Alternatives: •Nuclear Power Plant on the Moon •Beamed Power from Space Solar Power Plant

•Lunar open-pit mines for iron (est: 4 – 15% of lunar soil is Fe, occurring mostly as oxides). •Solar-heated metal extraction processes – vapor separation more viable than chemical reduction? •Robotic fabrication plant shipped to the Moon for box-cars, launcher rails, structural cables, conductors and magnets for launcher Alternatives: •Pre-fab delivery from Earth using tethers.

Delivery to the Moon Preferred Option: •Tether system. Alternatives: •Chemical rockets.

•Steel production on Mars, delivery to Moon. • Start with earth-delivered boxcars to build initial structure; Ship Fabrication plant to cylinder site; ship steel rods from Mars to cylinder site; land boxcars on Moon and reuse; •Asteroid resources.

•Nuclear rockets

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Launchers from the Moon Preferred Option: •Electromagnetic rail launcher sized to launch boxcar-sized loads at 8G, with carriage returning to starting point. •Power from local plants. •20 launchers placed around lunar Equator to enable round-the clock operation. Alternatives: • Tethers (problem: counterweight mass; repetition rate needed) •Nuclear rockets (need propellant gas)

•80-90% of power plant capacity utitlized by Cylinder project for 10 years; • Rest used for export of oxygen & tether counter-masses •Tethers and launchers form transportation system for industrial development on the Moon.

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Total market for lunar resources due to the Cylinder Project •

Steel 2.8 million tons over 11 years

•

Or Ti: 1.5 million tons over 11 years

•

Regolith: 50 billion tons over 11 years

•

Power: 44,600 GWh just for launch services; plus power for manufacturing.

•

Manufacturing: 314,000+ boxcars; 1600km of e-mag rails.

Notes: 1.

Radiation shield of 2m regolith is extremely conservative, and used only for illustration of very large-scale mass transport. Concepts for lunar hotel radiation shields use 0.4m of water with 0.1m rock wall. Shipping H2 from Earth and producing H2O in the cylinder site may cut the mass requirement by a factor of 30.

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Calculations

z Using

the E-mag Force Equation:

n1 := 1.51 n2 := 1.332 m :=

n1 n2

λ ( a) := 20 ⋅a k ( a) :=

wavelength

2 ⋅π λ ( a)

wavenumbe

c = speed of light in vacuum, m/s rho = density of material being shaped (sand = 2000 kg/m^3)

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Cost-Technology Matrix Approach •Consider the implications of synergizing technologies, with each providing assured markets / supplies / raw materials for others. •Alternative technologies for each major component of the project. •Risks mitigated by laying out alternative products and intermediate markets for each major technology developed for the project. •Cost-Technology Matrix Approach (C-TMA)TM - factors risks and market elasticity, to select from available technologies. •Weighs technologies quantitatively on the basis of cost, and ranks qualitatively by risk-rating against Technology, Ecology and Political Environment. The Cost Structure divided into 4 components: •Conceptualization Costs. •Capital Costs Operational Costs •Terrestrial Administrative Costs

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Estimating the required area needed using solar cells

z z

Solar Intensity from Sun at 1 AU is 1367 W/m2 Uncertainty in Solar Cell Efficiencies – Present Day Earth-Built Cell Tech. (32%) – Present Day Lunar-Built Cell Tech. (5%) – 30 Year Lunar-Built Cell Tech. (29%)

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ACOUSTIC FIELD RESULTS In micro-gravity, solid particles in a resonant chamber assume stable locations along surfaces parallel to nodal planes of the standing-wave. Liquids in finite-g form walls along nodes – which are regions of lower static pressure.

Irregular grain: microgravity

Hollow Al2O3 and Al spheres: microgravity

Powder suspended in water: 1-g

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School of Aerospace Engineering, Georgia Institute of Technology

OBSERVATIONS & CURRENT PLANS – ACOUSTIC SHAPING •G-Jitter effects – For a given jitter amplitude, walls survive high-frequency jitter better than low-frequency jitter because particles stay inside the nodal trap. •Long-duration micro-g needed to harden solid objects. •SEM experiment “Student Experiment in Microgravity” Powered experiment being developed for STS launch in 2003. Miniaturized, automated electronics package; small cylindrical resonator to produce hardened disk of cured resin. Total < 6lb. •GAS experiment “Getaway Special”. Larger 30lb payload. More instrumented experiment, being developed for 2004 timeframe. •Common objectives: •Bring back solid sample for materials / structural analysis. •Record formation and curing process.

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Continuing Work Areas •Acoustic & E-mag Simulations into the Mie regime & complex modes. •Mechanics of E-Mag construction: antenna & resonator design •Pulverization of asteroids •Melting/sintering in place to harden structures. •Conceptual Design: Space Experiment on E-Mag construction •Technology / market risk analysis - Long waves for asteroid reconstitution - Lunar power options - Lunar launch & delivery options - Shepherd spacecraft options •Costing approaches including synergy effects of Space-based economy plan

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