Lecture 01

Introduction to Satellite Communications

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The class notes used in this course are based on two different sets of class notes provided by Dr. Jeremy Allnutt and Dr. James W. LaPean when teaching “Satellite Communications” courses. Material from Leila Ribeiro is also used. All material is used with the permission of the author.

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Agenda • History • Overview and Basic concepts of Satellite Communications • Spectrum Allocation • Satellite Systems Applications • System Elements • System Design Considerations 3 • Current Developments and Future Trends

Important Milestones (before 1950) Putting the concepts together 1600 Tycho Brache’s experimental observations on planetary motion. 1609-1619 Kepler’s laws on planetary motion 1926 First liquid propellant rocket lauched by R.H. Goddard in the US. 1927 First transatlantic radio link communication 1942 First successful launch of a V-2 rocket in Germany. 1945 Arthur Clarke publishes his ideas on geostationary satellites for worldwide communications (GEO concept).

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Propulsion Rocket motors produce thrust in a process which can be explained by Newton's third law (for every action there is an equal but opposite reaction). In the case of rocket engines, the reactionary force is produced by the combustion of fuel in a combustion chamber. This force then acts upon the rocket nozzle, causing the reaction which propels the vehicle. Since rocket motors are designed to operate in space, they require an oxidizer in order for combustion to take place. This oxidizer is, in many cases, liquid oxygen. There are three different types of rocket engines: • 1. Solid propelled rockets • 2. Liquid propelled rockets • 3. Nuclear rockets The advantages and disadvantages of each type are shown below. Solid Fueled Rockets In solid fueled rockets, the fuel and oxidizer both in solid form and thoroughly mixed during manufacture. The section where the fuel is stored is also the combustion chamber. One end of the chamber is closed (the payload of the rocket would be attached to this end) and the other end of the chamber is a rocket nozzle. Advantages of solid fuel rockets include simplicity and reliability, since there are no moving parts and high propellant density, which results in a smaller sized rocket. Among the disadvantages are these: once you turn on a solid rocket motor, you can't shut it off. You have to wait for the fuel to run out. Also, the thrust of a solid fuel rocket decreases greatly during its burn time. Liquid Fueled Rockets In liquid fueled rockets the fuel and oxidizer are stored in liquid form and pumped into the combustion chamber. There are two types of liquid propellent rockets; bi-propellant rockets, which have separate fuel and oxidizer, and mono-propellant rockets, which have their fuel and oxidizer combined into a single liquid. Liquid fueled rockets are superior to solid fuel rockets in many respects; they can be shut off and subsequently restarted, they generally have a higher exhaust velocity, which means lower burn times are required, and they can be throttled to produce more or less thrust, as needed. However, liquid fuel rockets are highly complex, and therefore have a lower rate of reliability. Nuclear Rockets Nuclear rockets work by routing hydrogen through a nuclear reactor. The reactor is at a high temperature, which causes the hydrogen fuel to expand as it leaves the nozzle, producing a high amount of thrust. Nuclear rockets do not need an oxidizer, and they require much less fuel per pound of payload than liquid or solid fuel rockets. This allows a vehicle using a nuclear rocket to be more versatile than one which uses chemical rockets. Disadvantages of nuclear rockets include radiation effects caused by the nuclear reactor, and the high weight of the engine assembly. Odysseus Recent studies have shown nuclear propulsion for Mars missions offers several major advantages over all-chemical propulsion systems. Therefore, a nuclear engine was selected for the Odysseus program. The Oddyseus II engine will produce 1,112,500 Newtons of thrust at a weight of 9100 kg. The engine will be approximately 3m in diameter and 6 meters long. 5

 

V2 Rocket

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Important Milestones (1950’s) Putting the pieces together 1956 - Trans-Atlantic cable opened (about 12 telephone channels – operator). 1957 First man-made satellite launched by former USSR (Sputnik, LEO). 1958 First US satellite launched (SCORE). First voice communication established via satellite (LEO, lasted 35 days in orbit after batteries failed).

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Sputnik - I

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Explorer - I

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Important Milestones (1960’s) First satellite communications 1960 First passive communication satellite launched into space (Large balloons, Echo I and II). 1962: First non-government active communication satellite launched Telstar I (MEO). 1963: First satellite launched into geostationary orbit Syncom 1 (comms. failed). 1964: International Telecomm. Satellite Organization (INTELSAT) created. 1965 First communications satellite launched into geostationary orbit for commercial use Early Bird (re-named INTELSAT 1).

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ECHO I

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Telstar I

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Intelsat I

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Important Milestones (1970’s) GEO applications development 1972 First domestic satellite system operational (Canada). INTERSPUTNIK founded. 1975 First successful direct broadcast experiment (one year duration; USA-India). 1977 A plan for direct-to-home satellite broadcasting assigned by the ITU in regions 1 and 3 (most of the world except the Americas). 1979 International Mobile Satellite Organization (Inmarsat) established.

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Important Milestones (1980’s) GEO applications expanded 1981 First reusable launch vehicle flight. 1982 International maritime communications made operational. 1983 ITU direct broadcast plan extended to region 2. 1984 First direct-to-home broadcast system operational (Japan). 1987 Successful trials of land-mobile communications (Inmarsat). 1989-90 Global mobile communication service extended to land mobile and aeronautical use (Inmarsat)

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Important Milestones (1990’s) 1990-95: - Several organizations propose the use of non-geostationary (NGSO) satellite systems for mobile communications. - Continuing growth of VSATs around the world. - Spectrum allocation for non-GEO systems. - Continuing growth of direct broadcast systems. DirectTV created. 1997: - Launch of first batch of LEO for hand-held terminals (Iridium). - Voice service telephone-sized desktop and paging service pocket size mobile terminals launched (Inmarsat). 1998: Iridium initiates services. 1999: Globalstar Initiates Service. 2000: ICO initiates Service. Iridium fails and system is sold to Boeing.

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Iridium

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Overview and Basic concepts of Satellite Communications

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Main orbit types:

GEO

36,000 km

MEO

5,000 – 15,000 km

LEO

500 -1000 km

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USEFUL ORBITS 1: GEOSTATIONARY ORBIT In the equatorial plane Orbital Period = 23 h 56 min. 4.091 s = one Sidereal Day (defined as one complete rotation relative to the fixed stars) Satellite appears to be stationary over a point on the equator to an observer Radius of orbit, r, = 42,164.57 km

NOTE: Radius = orbital height + radius of the earth Average radius of earth = 6,378.14 km

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USEFUL ORBITS 2: Low Earth Orbit (>250 km); T ≈ 92 minutes Polar (Low Earth) Orbit; earth rotates about 23o each orbit; useful for surveillance Sun Synchronous Orbit(example, TirosN/NOAA satellites used for search and rescue operations) 8-hour and 12-hour orbits Molniya orbit (Highly Elliptical Orbit (HEO); T ≈ 11h 38 min; highly eccentric orbit; inclination 63.4 degrees

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MOLNIYA VIEW OF THE EARTH (Apogee remains over the northern hemisphere)

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Molniya Variants (HEO’s) Tundra Orbit – Lies entirely above the Van Allen belts. The Russian Tundra system, which employs two satellites in two 24-hour orbits separated by 180 deg around the Earth, with an apogee of 53,622 km and a perigee of 17,951 km. The Molniya orbit crosses the Van Allen belts twice for each revolution, resulting in a reduction of satellite life due to impact on electronics the Russian Molniya system employs three satellites in three 12-hour orbits separated by 120 deg around the Earth, with an apogee of 39,354 km and a perigee of 1000 km.

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Molniya Variants (HEO’s) The LOOPUS orbit.The LOOPUS system employs three satellites in three eight-hour orbits separated by 120 deg around the Earth, with an apogee of 39,117 km and a perigee of 1238 km. The ELLIPSO orbit

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A Highly Elliptical Orbit (HEO) A satellite in HEO typically has a perigee at about 500 km above the surface of the Earth and an apogee as high as 50,000 km. The orbit is usually inclined at 63.4 deg to provide communications services to locations at high northern latitudes. This inclination value is selected to avoid rotation of the apses; thus, a line from the Earth's center to the apogee always intersects the Earth's surface at a latitude of 63.4 deg North. Orbit period varies from eight to 24 hours. Owing to the high eccentricity of the orbit, a satellite spends about two-thirds of the orbital period near apogee, during which time it appears to be almost stationary to an observer on the Earth (a phenomenon known as `apogee dwell'). During the brief time the satellite is below the local horizon, a hand-off to another satellite in the same orbit is required in order to avoid loss of communications. Free space loss and propagation delay for this type of orbit are comparable to that of geosynchronous satellites. However, due to the comparatively great movement of a satellite in HEO relative to an observer on the Earth, satellite systems using this type of orbit must cope with large Doppler shifts. 25

A Medium-Earth Orbit (MEO) By setting the altitude parameters at 10,000 km, you generated a medium-Earth orbit (MEO). This one happens to be an Intermediate Circular Orbit (ICO), since the apogee and perigee are equal. Its orbit period measures about seven hours. The maximum time during which a satellite in MEO orbit is above the local horizon for an observer on the Earth is a few hours. A global communications system using this type of orbit requires relatively few satellites in two to three orbital planes to achieve global coverage. MEO systems operate similarly to LEO systems. In MEO systems, however, hand-over is less frequent, and propagation delay and free space loss are greater. Examples of MEO (specifically ICO) systems are Inmarsat-P (10 satellites in 2 inclined planes at 10,355 km), and Odyssey (12 satellites in 3 inclined planes, also at 10,355 km).

A Low-Earth Orbit (LEO) By selecting a relatively short period (90 minutes), we have generated a satellite in low-Earth orbit (LEO). A typical LEO is elliptical or, more often, circular, with a height of less than 2000 km above the surface of the Earth. The orbit period at those altitudes ranges between 90 minutes and two hours. The radius of the footprint of a communications satellite in LEO ranges between 3000 and 4000 km. The maximum time during which a satellite in LEO is above the local horizon for an observer on the Earth is 20 minutes. A global communications system using this type of orbit requires a large number of satellites, in a number of different orbital planes. When a satellite serving a particular user moves below the local horizon, it must hand over its duties to a succeeding one in the same orbit or in an adjacent one. Due to the comparatively great movement of a satellite in LEO relative to an observer on the Earth, satellite systems using this type of orbit must cope with large Doppler shifts. Satellites in LEO are also affected by atmospheric drag that causes the orbit to gradually deteriorate. Examples of major LEO systems are GlobalstarTM (48+8 satellites in 8 orbital planes at 1400 km) and Iridium® (66+6 satellites in 6 orbital planes at 780 km). There are also a number of small LEO systems, such as PoSat, built by SSTL in 1993 and launched into an 822 by 800 km orbit, inclined at 98.6 deg. 26

Geosynchronous & Geostationary Orbits

A geosynchronous orbit is defined as an orbit with a period of one sidereal day (1436.1 minutes). A geostationary orbit is a special case of a geosynchronous orbit with zero inclination and zero eccentricity, i.e., an equatorial, circular orbit. A satellite in a geostationary orbit appears fixed above a location on the surface of the Earth. In practice, a geosynchronous orbit typically has small non-zero values for inclination and eccentricity, causing the satellite to trace out a small figure eight in the sky. The footprint or service area of a geosynchronous satellite covers almost one-third of the Earth's surface (from about 75 deg South to about 75 deg North latitude), so that near-global coverage can be achieved with as few as three satellites in orbit. A disadvantage of a geosynchronous satellite in a voice communication system is the round-trip delay of approximately 250 milliseconds.

A Polar Orbit

The plane of a polar orbit is inclined at about 90 deg to the equatorial plane, intersecting the North and South poles. The orbit is fixed in space, and the Earth rotates underneath. Thus, in principle, the coverage of a single satellite in a polar orbit encompasses the entire globe, although there are long periods during which the satellite is out of view of a particular ground station. This gap in coverage may be acceptable for a store-and-forward communications system. Accessibility can, of course, be improved through the deployment of two or more satellites in different polar orbits. Most small LEO systems employ polar or near-polar orbits. An example is the COSPAS-SARSAT Maritime Search and Rescue system, which uses eight satellites in near polar orbits: four SARSAT satellites moving in 860 km orbits inclined at 99 deg (which makes them Sunsynchronous) and four COSPAS satellites moving in 1000 km orbits inclined at 82 deg.

A Sun-Synchronous Orbit

In a Sun-synchronous or helio-synchronous orbit, the angle between the orbital plane and Sun remains constant, resulting in consistent light conditions for the satellite. This can be achieved by careful selection of orbital altitude, eccentricity and inclination, producing a precession of the orbit (node rotation) of approximately 1 deg eastward each day, equal to the apparent motion of the Sun. This condition can be achieved only for a satellite in a retrograde orbit. A satellite in Sun-synchronous orbit crosses the equator and each latitude at the same time each day. This type of orbit is therefore advantageous for an Earth observation satellite, since it provides constant lighting conditions.

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Parameters Determining Orbit Size and Shape Parameter

Definition

Semimajor Axis

Half the distance between the two points in the orbit that are farthest apart

Apogee/Perigee Radius

Measured from the center of the Earth to the points of maximum and minimum radius in the orbit

Apogee/Perigee Altitude

Measured from the "surface" of the Earth (a theoretical sphere with a radius equal to the equatorial radius of the Earth) to the points of maximum and minimum radius in the orbit

Period

The duration of one orbit, based on assumed two-body motion

Mean Motion

The number of orbits per solar day (86,400 sec/24 hour), based on assumed two-body motion

Eccentricity

The shape of the ellipse comprising the orbit, ranging between a perfect circle (eccentricity = 0) and a parabola (eccentricity = 1)

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Orientation of Orbital Plane in Space Parameter

Definition

Inclination

The angle between the orbital plane and the Earth's equatorial plane (commonly used as a reference plane for Earth satellites)

Right Ascension of the Ascending Node

The angle in the Earth's equatorial plane measured eastward from the vernal equinox to the ascending node of the orbit

Argument of Perigee

The angle, in the plane of the satellite's orbit, between the ascending node and the perigee of the orbit, measured in the direction of the satellite's motion

Longitude of the Ascending Node

The Earth-fixed longitude of the ascending node

The ascending node (referenced in three of the above definitions) is the point in the satellite's orbit where it crosses the Earth's equatorial plane going from south to north.

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Parameters determining orbit orientation

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Satellite Location parameters To specify the satellite's location within its orbit at epoch.

Parameter

Definition

True Anomaly

The angle from the eccentricity vector (points toward perigee) to the satellite position vector, measured in the direction of satellite motion and in the orbit plane.

Mean Anomaly

The angle from the eccentricity vector to a position vector where the satellite would be if it were always moving at its angular rate.

Eccentric Anomaly

An angle measured with an origin at the center of an ellipse from the direction of perigee to a point on a circumscribing circle from which a line perpendicular to the semimajor axis intersects the position of the satellite on the ellipse.

Argument of Latitude

The sum of the True Anomaly and the Argument of Perigee.

Time Past Ascending Node

The elapsed time since the last ascending node crossing.

Time Past Perigee

The elapsed time since last perigee passage.

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Parameters determining satellite position

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Orbital Velocities and Periods Satellite System

Orbital Height (km)

INTELSAT

35,786.43

3.0747

23 56 4.091

ICO-Global

10,255

4.8954

5 55 48.4

1,469

7.1272

1 55 17.8

780

7.4624

1 40 27.0

Skybridge Iridium

Orbital Velocity (km/s)

Orbital Period h min s

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GSO AND NGSO FACTORS NGSO OPTIONS: LEO MEO HEO

AVOID RADIATION BELTS IF POSSIBLE 35

Coverage vs. Altitude

Satellite Altitude (km)

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LEO, MEO and GEO Orbit Periods 30.0

25.0

Hours

20.0

15.0

10.0

5.0

0.0 0

5000

10000

15000

20000

25000

30000

35000

40000

Altitude [km]

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Minimum Delay for two hops 300.0

250.0

Delay [ms]

200.0

150.0

100.0

50.0

0.0 0

5000

10000

15000

20000

25000

30000

35000

40000

Altitude [km]

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Why do satellites stay moving and in orbit?

v (velocity) F2 F1 (Gravitational Force)

(Inertial-Centrifugal Force)

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Spectrum Allocation

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Frequency Spectrum concepts: • Frequency: Rate at which an electromagnetic wave reverts its polarity (oscillates) in cycles per second or Hertz (Hz). • Wavelength: distance between wavefronts in space. Given in meters as: λ = c/f Where: c = speed of light (3x108 m/s in vacuum) f = frequency in Hertz • Frequency band: range of frequencies. • Bandwidth: Size or “width” (in Hertz) or a frequency band. • Electromagnetic Spectrum: full extent of all frequencies from zero to infinity. 41

Radio Frequencies (RF)

RF Frequencies: Part of the electromagnetic spectrum ranging between 300 MHz and 300 GHz. Interesting properties: Efficient generation of signal power Radiates into free space Efficient reception at a different point. Differences depending on the RF frequency used: - Signal Bandwidth - Propagation effects (diffraction, noise, fading) - Antenna Sizes

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Microwave Frequencies

• Sub-range of the RF frequencies approximately from 1GHz to 30GHz. Main properties: - Line of sight propagation (space and atmosphere). - Blockage by dense media (hills, buildings, rain) - Wide bandwidths compared to lower frequency bands. - Compact antennas, directionality possible. - Reduced efficiency of power amplification as frequency grows: Radio Frequency Power OUT Direct Current Power IN

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Spectrum Regulation International Telecommunication Union (ITU): Members from practically all countries around the world. • Allocates frequency bands for different purposes and distribute them around the planet. • Creates rules to limit RF Interference (RFI) between countries that reuse same RF bands. • Mediates disputes and creates rules to deal with harmful interference when it occurs. • Meets bi-annually with its members, to review rules and allocations: World Radio Communication Conference (WRC). • There are also the Regional Radio Communication Conferences (RCC), which happen less often.

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Radio Frequency Spectrum Commonly Used Bands

0.1

AM

HF

VHF

1

10

100

UHF

L S 1

MHz

SHF C X Ku Ka V Q 10

100

GHz

Terrestrial Bands Space Bands Shared (Terrestrial and Space)

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Space-Earth Frequency Usability

Resonance frequencies below 100GHz: • 22.2GHz (H20) • 53.5-65.2 GHz (Oxygen)

Atmospheric attenuation effects for Space-to-Earth as a function of frequency (clear air conditions). (a) Oxygen; (b) Water vapor. [Source: ITU © 1988] 46

Insights on Frequency Selection: (Part 1: Lower frequencies, stronger links) LEO satellites need lower RF frequencies: Omni-directional antennas on handsets have low gain typically G = 0 db = 1 Flux density F in W/m2 at the earth’s surface in any beam is independent of frequency Received power is F x A watts , where A is effective area of antenna in square meters For an omni-directional antenna A = G λ 2/ 4 π = λ 2/ 4π At 450 MHz, A = 353 cm2, at 20 GHz, A = 0.18 cm2 Difference is 33 dB - so don’t use 20 GHz with an omni! 47

Insights on Frequency Selection: (Part 2: Higher frequencies, higher capacity) GEO satellites need more RF frequencies High speed data links on GEO satellites need about 0.8 Hz of RF bandwidth per bit/sec. A 155 Mbps data link requires 125 MHz bandwidth Available RF bandwidth: C band occupied) Ka band Q/V band

Ku band 2000 MHz

750 MHz

500 MHz

(All GEO slots

(Most GEO slots occupied)

(proliferating)

?

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Satellite Systems Applications

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Initial application of GEO Satellites: Telephony 1965 circuits 1968 1986 2000 power

Early Bird 34 kg

240 telephone

Intelsat III 152 kg 1500 circuits Intelsat VI 1,800 kg 33,000 circuits Large GEO 3000 kg 8 - 15 kW 1,200 kg payload

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Current GEO Satellite Applications: Broadcasting - mainly TV at present DirecTV, PrimeStar, etc.

Point to Multi-point communications VSAT, Video distribution for Cable TV

Mobile Services Motient (former American Mobile Satellite), INMARSAT, etc.

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Satellite Navigation: GPS and GLONASS GPS is a medium earth orbit (MEO) satellite system GPS satellites broadcast pulse trains with very accurate time signals A receiver able to “see” four GPS satellites can calculate its position within 30 m anywhere in world 24 satellites in clusters of four, 12 hour orbital period “You never need be lost again” Every automobile and cellular phone will eventually have a GPS location read-out

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LEO Satellites in year 2000 Several new systems are just starting service Circular or inclined orbit with < 1400 km altitude Satellite travels across sky from horizon to horizon in 5 - 15 minutes Earth stations must track satellite or have omnidirectional antennas Constellation of satellites is needed for continuous communication. Handoff needed. 53

System Elements

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Satellite System Elements Space Segment Satellite

Earth Stations

Coverage Region

SCC TT&C Ground Station

Ground Segment 55

Space Segment – – – –

Satellite Launching Phase Transfer Orbit Phase Deployment Operation

TT&C - Tracking Telemetry and Command Station:

Establishes a control and monitoring link with satellite. Tracks orbit distortions and allows correction planning. Distortions caused by irregular gravitational forces from non-spherical Earth and due to the influence of Sun and Moon forces.

SSC - Satellite Control Center, a.k.a.: – OCC - Operations Control Center – SCF - Satellite Control Facility

Provides link signal monitoring for Link Maintenance and Interference monitoring.

– Retirement Phase

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Types of Satellite Stabilization Spin Stabilization Satellite is spun about the axis on which the moment of inertia is maximum (ex., HS 376, most purchased commercial communications satellite; first satellite placed in orbit by the Space Shuttle.)

Three-Axis Stabilization Bias momentum type (ex., INTELSAT V) Zero momentum type (ex., Yuri)

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Satellite Subsystems Communications Antennas Transponders

Common Subsystem (Bus Subsystem) Telemetry/Command (TT&C) Satellite Control (antenna pointing,attitude) Propulsion Electrical Power Structure Thermal Control

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Ground Segment Collection of facilities, users and applications.

FSS – Fixed Satellite Service

MSS – Mobile Satellite Service

Earth Station = Satellite Communication Station (air, ground or sea, fixed or mobile). 59

System Design Considerations

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Basic Principles Satellite

Uplink

Downlink

Earth Station

Earth Station

Tx

Source Information

Output Information

Rx

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Signals Signals: Carried by wires as voltage or current Transmitted through space as electromagnetic waves. Analog: • Voltage or Current proportional to signal; e.g., Telephone.

Digital: Generated by computers. Ex. Binary = 1 or 0 corresponding to +1V or –1V.

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Separating Signals Up and Down: FDD: Frequency Division Duplexing. f1 = Uplink f2 = Downlink

TDD: Time Division Duplexing. t1=Up, t2=Down, t3=Up, t4=Down,….

Polarization V & H linear polarization RH & LH circular polarizations

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Separating Signals (so that many transmitters can use the same transponder simultaneously)

Between Users or “Channels” (Multiple Access): FDMA: Frequency Division Multiple Access; assigns each transmitter its own carrier frequency f1 = User 1; f2 = User 2; f3 = User 3, …

TDMA: Time Division Multiple Access; each transmitter is given its own time slot t1=User_1, t2=User_2, t3=User_3, t4 = User_1, ...

CDMA: Code Division Multiple Access; each transmitter transmits simultaneously and at the same frequency and each transmission is modulated by its own pseudo randomly coded bit stream Code 1 = User 1; Code 2 = User 2; Code 3 = User 3

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Digital Communication System TRANSMITTER Source Data

Source Coding

Channel Coding

Modulator

RF Channel Output Data

Source Decoding

Channel Decoder

Demodulator

RECEIVER

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Current Developments and Future Trends

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Current Trends in Satellite Communications Bigger, heavier, GEO satellites with multiple roles More direct broadcast TV and Radio satellites Expansion into Ka, Q, V bands (20/30, 40/50 GHz) Massive growth in data services fueled by Internet Mobile services: May be broadcast services rather than point to point Make mobile services a successful business? 67

The Future for Satellite Communications – 1 Growth requires new frequency bands Propagation through rain and clouds becomes a problem as RF frequency is increased C-band (6/4 GHz) Rain has little impact availability is possible Ku-band (10-12 GHz) 99.8% availability

99.99%

Link margin of ≥ 3 dB needed for

Ka-band (20 - 30 GHz) Link margin of ≥ 6 dB needed 99.6% availability

for

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The Future for Satellite Communications - 2 Low cost phased array antennas for mobiles are needed Mobile systems are limited by use of omnidirectional antennas A self-phasing, self-steering phased array antenna with 6 dB gain can quadruple the capacity of a system Directional antennas allow frequency re-use 69

TUTORIAL SHEET 01 . 1) How many satellites does Dish Network have in the sky? Name them? 2) How many transponders are on each of these satellites? What frequency band is used? 3) What orbit are these satellites in (LEO, MEO, GEO)? 4) Why are two heads used on the Dish Network antenna (text page 445)? 5) On what date was Echostar I launched? Echostar V? 6) Are these satellites spin or three axis stabilized? See page 443 7) Go to the Website and download the azimuth and elevation application( products – installation) and follow the directions to aim the dish antenna to receive a signal for the zip code where you live. State the azimuth, elevation and skew angles and longitude for each satellite. 8) See page 443. If the frequency band were C rather than Ku, how would this affect the size of the receive antenna you would need on your rooftop? 9) What is a transponder? Why does a satellite have multiple transponders and not just one? 10) Extra credit – Go to the Air & Space Museum and view Explorer I, Sputnik I, the V2 rocket, TIROS II, TIROS-N and ITOS. Briefly describe the purpose of each.

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