kepler's law kepler’s first law – the orbit of any planet is an ellipse with the sun at one...

Kepler's LawKepler’s First Law – the orbit of any planet is

an ellipse with the sun at one focus

Kepler’s Second Law; Law of Areas – every planet moves so that its radius sector sweeps over equal areas in equal intervals of time.

Kepler's Law

Kepler’s Third Law; Law of Periods – the square of the periods of revolution of any two planets is to each other as the cubes of their respective mean distances from the sun.

Kepler's Law

Launching the Satellite

Space shuttles carry some satellites into space

Many satellites require minor adjustments of their orbit before they begin to perform their function. Built-in rockets called thrusters, some as small as a propelling pencil, make these adjustments.

Once a satellite is placed into a stable orbit, it can remain there for a long time without further adjustment.


Rocket Motors - Communications satellites are lifted into

orbit by space vehicles, which are launched vertically for structural and aerodynamic reasons. Rocket motors provide the power for these vehicles. Rocket motors do not depend on the atmosphere for oxidizing or burning fuel. They may classify as solid or liquid propellant motors

Solid Propellant Rockets

- Works on the principle similar to small gunpowder rockets used for fireworks displays. It contains grain fuel, a combination of combustible material and oxidizer. Fuel is burned in a restricted combustion space with nozzles to direct and accelerate the outgoing gas flow. Directional control is achieved by placing restructures or deflectors to change the direction of thrust.


They are usually used for upper stages of multiple stage vehicles such as the Polaris.

Liquid Propellant Rockets - Carries two tanks

outside the combustion chamber, one for fuel and the other for the oxidizer.


Components of Satellite Systems

1. Earth Station and Uplink Components

- Earth Station is that portion of satellite link which receive, processes and transmits communications between the earth and a satellite

Functions

a. Receiving IF signals from one or more modulators

b. Transition of IF signals to RF signals

c. Transmission of signals to satellites

d. Receiving signals from the satellite

e. Translating RF signals into IF signals


Major Subsystems

a. The power subsystem

b. Terrestrial interface

c. Transmit and receive chain

d. Antenna

e. Control sub-systems


Components of Earth Station

a. IF Modulator – converts input baseband signal to FM, QAM IF

b. IF-RF Microwave Up Converter – converts IF to RF carrier frequencies

c. High Power Amplifier (HPA) – provides adequate input sensitivity and output power to propagate signal transponder using a TWT or Klystron.

d. Output Band Pass Filter – limits bandwidth



Modulator

Base Band in FDM or PCM/TDM

BPF Mixer BPF

Microwave Generator

HPAIF RF

UpConverter

Components of Satellite Assembly

a. Command and control antenna

b. Global coverage antenna

c. Orbit – maneuvering engine for orbit and altitude adjustment stabilization.

d. Power supply or generator – solar cell array and batteries

e. Inertial guidance systems

f. Heat control

g. Telemetry equipment


2. Transponder Components

- microwave repeaters carried by communication satellites. Transponders have the following function: receiving, amplification, frequency conversion and retransmission.


Components

a. Input Band Limiting Device – limits total noise applied to LNA input.

b. Input Low Noise Amplifier (LNA) – amplifies signals, usually a tunnel diode

c. Frequency Translator – shift oscillator, which converts highband uplink frequency to lowband downlink frequency

d. Low-Level Power Amplifier – amplifies (TWT) RF signal for transmission through the downlink to station receiver.

e. Output Bandpass Filter – limits output bandwidth



BPF LNA Mixer BPF

MicrowaveShift Oscillator

2 GHz

LNA

FrequencyTranslator

3. Downlink Components

a. Bandpass Filter (BPF) – limits input noise power to LNA

b. Low Noise Amplifier (LNA) – highly sensitive, low noise device usually a tunnel diode or parametric amplifier

c. RF-to-IF Down Converter – mixer / bandpass filter combination which converts the received RF signal to an IF frequency


BPF LNA Mixer BPF

MicrowaveGenerator

Demodulator

DownConverter


Frequency Allocations

Choice of Frequency

- primarily dictated by the external and internal noise sources that contribute to the noise system temperature and by the existence of spectral window for which signal attenuation is small.

- The following factors must be considered sources of noise and attenuation such as cosmic noise, sunspot activity, Faraday rotation, ionosphere scintillations, rain and snow.

- C band is the most commonly used band.

- Ku band is immune to terrestrial jamming but sensitive to atmospheric conditions such as transient noise

- The Ka-band has the strongest signal and higher data rate capability. It is highly directional and has a spot coverage

- X band – military

- L band

Frequency Spacing

- Geosynchronous satellites share a limited space and frequency spectrum within a given area of geostationary orbit. Each is assigned a longitude spaced between 3 to 6 degrees in the arc approximately 22,300 miles above the equator


Uplink and downlink frequency bands - The uplink frequency is always higher than the

downlink by 2225 MHz because higher frequency offers greater spreading or Free Space Loss than lower frequencies.

Frequency Reuse Methods

- Frequency reuse is a technique employed in order to conserve electromagnetic frequencies resources, they can be implemented by the following methods:


Multiple Coverage Areas - the use of the same

frequency beamed towards different geographic areas on earth multiple spot beam antennas.

Dual polarization – sending different information signals using vertical or horizontal electromagnetic polarization. This is similar to Polarization Diversity in order to improve system stability


- a geographic representation of a satellite’s radiation pattern, with contour lines representing limits of equal receive power density.

Satellite Footprint

1. Spot Coverage – beams concentrate the radiated power in a very small geographic area

2. Zonal Coverage – covers less than one-third of earth’s surface

3. Earth Coverage – covers approximately one-third of earth's surface (42 %) using a 17-degree beamwidth

Satellite Types as to Territorial Coverage

1. Global – covers the whole world

2. Regional – covers selected regions such as Pacific, Atlantic, etc.

3. National / Domestic – covers domestic or national territory

1. Fixed

2. Mobile

3. Broadcasting

4. Maritime

5. Aeronautical

Satellite Types as to Services Offered

6. Point-to-point

7. Military

8. Amateur

9. Experimental

Satellite Tracking1. Look Angle – the angle

measure from the horizontal to the point on the center of the main beam of the antenna when the antenna is pointed directly at the satellite

2. Angle of Elevation – angle formed between the plane of a wave from an earth station antenna and the horizon, or the angle subtended at the earth station antenna between the satellite and the earth’s horizon

3. Azimuth – the horizontal pointing angle of an antenna measured in degrees in a clockwise direction from true North

Satellite Height

h =gr2T2

4π2( )1

3

where: g = acceleration due to gravity; 9.81 m/s2

r = earth radius; 6400 km T = time in second to make a complete orbit

Satellite Velocity

4 x 1011

6400 + hkm

; m/sν s =

Satellite System Design Parameters

Factors in Satellite Design

1. Transmit Power or Effective Radiated Power – the product of the total antenna radiated power and its gain.

2. Equivalent Noise Temperature – the ratio between the Noise Power and the product of the Bandwidth and Boltzmann constant.

3. Noise Density – total noise power normalized to 1 hertz bandwidth.

4. Satellite Control

– involves actions necessary to position, tract, monitor, and command the satellite during the course of its operational life. It involves supervising and monitoring the establishment, configuration and control of each required of link through satellite transponder in accordance with desired parameters. The two main aspects of satellite control are orientation and position control.


a. Orientation – is required in a communications satellite for initial orientation and for all subsequent adjustment so the antenna will constantly view the earth and the solar cells will view the sun

b. Position Control – is required for initial satellite emplacement and to compensate for forces which tends to divert the satellite from its orbit. Such forces include lunar and solar gravitational action.

c. Orientation Control - attitude control of a vehicle about any or all of its axes (roll, pitch and yaw) projects for axial, radial axis and corrections.


5. Spin Stabilization – operates on the principle that the direction of the spin axis of a rotating body tends to remain fixed inertial space. It requires no additional energy or expenditure of mass once the system is in motion

6. Gravity Gradient Stabilization – requires no power or expendable mass once deployed and allows more of satellite electrical power and weight for communications purposes.

7. Station Keeping – is the control routing necessary to keep the satellite in position.

8. Circuit Control – involves actions necessary to assure that the required circuits between all authorized users are established, maintained and restored satisfactorily, a function performed by technical control facilities personnel


Satellite Accessing TechniqueAccess Techniques - refers to the way a communications system uses a satellite

transponder.

Multiple Access - in communications satellites, those satellites so equipped that

they may function as a portion of a communications link between more than one pair of ground stations simultaneously.

Multiple Access Back-Off – refers to the satellite output power that is lost due to the necessity for backing off on earth station radiated power to avoid generating excessively high intermodulation products in the satellite. It ranges from 1 to 2 dB

Satellite Multiple Access Technique

1. Frequency Division Multiple Access (FDMA) – a satellite transponder is divided into smaller

frequencies hand segments where each segment is assigned to use for his uplink or downlink frequency.

a. Pre-assigned – a given number of available voice hand channels from each earth station are assigned dedicated destinations. This method is only economically feasible in situations where sources / destination locations have very low traffic density during the busy hour.

b. Demand Assigned (DAMA) – voice band channels are assigned on “as-needed” basis. It provides more versatility and more efficient use of the frequency spectrum.


Three Methods of Controlling DAMA Systems

a. Polling – a master station “polls” other stations sequentially. When a positive reply is received, a channel is assigned accordingly. As the polling interval becomes longer and the system tends to become unwieldy because of excessive post dial delay as a call attempt waits for the pulling interval to run its course


b. Random Access Central Control – a central computer located at the master station coordinates the status of the channels. Call requests are passed to the central computer and a channel is assigned if available. Once the call is completed and the subscriber goes on the hook, the speech path is taken down and the channel used is returned to the demand access pull of ideal channels.


c. Random Access Distributed Control – uses a processor controller at each earth station accessing the system. All earth stations in the network monitor the status information by means of the digital order wire circuit. When an idle channel is seized, all users are informed to the fact and the circuit is removed from the poll


SPADE – Single Channel Per Carrier PCM Multiple Access Demand Assignment Equipment – an 800-PCM encoded voice band channels separately QPSK modulate an IF carrier frequency. Each 4 kHz voice band channel is sampled at an 8 kHz rate and converted into bit PCM CODE. This produces a 64 kbps PCM code for each band channel


2. Time Division Multiple Access (TDMA)

- works in the time domain and is applicable to digital systems because information storage is required. In this method, stations are restricted to precise time slot. It has no restrictions on frequency or bandwidth. Presently, it is the most dominant method used of providing the most efficient method of transmitting digitally modulated carries (PSK).


- each earth station transmits a short burst of a digitally modulated carrier during a precise time slot which TDMA frame. Each burst is synchronized so that it arrives at the satellite transponder at a different time avoid collision with another station's carrier. It is a “store-and-forward” system whereby earth stations, can consult only during their specified time slot, although the incoming voice had signals is continuous.


- in TDMA, only one user appears on the transponder at any given time. Each user is assigned a time slot to the satellite; transponder power and bandwidth are shared by several earth stations.


Store and Forward – a technique in which a message received from earth termed is held in storage until the satellite is in view of a second earth terminal, at which time the message is transmitted.


3. Code Division Multiple Access (CDMA) or Spread Spectrum Multiple Access (SSMA)

- each station may transmit whenever it wishes and can use any or all of the bandwidth allocated. Transmissions are separated through envelope, encryption, and decryption techniques. It uses unique binary words called CHIP CODES to receive a particular earth station’s transmission.


- a correlator checks or compares orthogonal codes with original chip codes to allow access to users

- the transmitted signal is spread over part or all of the available transponder hand width in a time-frequency relationship by a code transformation. Typically, the modulated carrier is ten to hundreds of times greater than the information bandwidth.


Frequency Hopping – is a form of CDMA where a digital code is used to continually change the frequency of the carrier. The total available bandwidth is partitioned to smaller frequency bands and total transmission time is subdivided into smaller time slots. Each station uses the entire RF spectrum but never occupies more than a small portion of that spectrum at any one time.


Satellite Organizations

INMARSAT (International Maritime Satellite Organization)

- recommended by the panel of experts commissioned by the Intergovernmental Maritime Consultative Organization (IMCO). They consider the introduction of satellite communications to the maritime sphere with the aim of improving communications with ships, particularly for safety and distress purposes.

- born in July 1979, very much along the INTELSAT lines, with COMSAT as the largest shareholder.


INTELSAT (International Telecommunications Satellite

Consortium)

- Founded in 1964 at Washington D.C. by COMSAT (Communication Satellite Corporation) of the United States, Overseas Telecommunications Commission of the Australia and nine other world communications agencies


MARISAT

- a ship-to-shore and shore-to-ship communications via a dedicated geostationary satellite system, providing high-quality telephony, data and telex/telegraphy circuits


Questions1. The first passive satellitea. Telstarb. Early Birdc. Sputnik Id. Moon

Questions2. The first active satellitea. Sputnik I b. Telstarc. INTELSAT Id. Explorer I

Questions3.The first geostationary satellite launched in 1965 isa. Syncom Ib. Sputnik Ic. Explorer Id. Early Bird

Questions4. The average lifetime of geosynchronous satellites is about __________ years.

a. 5b. 10c. 15d. 20

Questions5. A communication satellite is a repeater

betweena. A transmitting station and receiving

stationb. Many transmitting stations and many

receiving stationsc. A transmitting station and many

receiving stationsd. Many transmitting stations and a

receiving station

Questions6. One of the main applications of

satellite communications is monitoring the ecological situation of the earth. This is known as

a. Navigationb. Surveillancec. Remote controld. Remote sensing

Questions7. What vacuum tube used to amplify

RF signal for transmission through the downlink to station receiver?a. Magnetronb. Klystronc. Twystrond. TWT

Questions8. A high power tube used in transmission of RF signal uplink

a. Magnetronb. Klystronc. BWOd. TWT

Questions9. A stage in transponder and downlink system which amplifies the signal and ensuring that noise is suppressed as possiblea. Mixerb. Demodulatorc. LNAd. IF amplifier

Questions10. A transponder is a satellite equipment whicha. Receives a signal from earth station and amplifies it

b. Changes the frequency of the received signal

c. Retransmit the received signald. All of the above

Questions11. Multiple repeaters in communications satellites are known as

a. Transpondersb. Detectorsc. Modulatorsd. Transceivers

Questions12. Satellite-to-satellite link is also called

a. Uplinkb. Downlinkc. Crosslinkd. Weakest link

Questions13. The expression for satellite link

frequencies such as 14/12 GHz denotes that

a. 12 GHz is the uplink frequency and 14 GHz is the downlink frequency

b. the system is operating at a mean frequency of 13 GHz

c. 14 GHz is the uplink frequency and 12 GHz is the downlink frequency

d. the 14 GHz frequency is backup for 12 GHz frequency or vice versa

Questions14. The most widely used microwave bands for commercial applications area. C band and X bandb. X band and S bandc. C band and Ku bandd. S band and Ku band

Questions15. At present, the RF band mainly used by most satellites isa. EHFb. UHFc. SHFd. VHF

Questions16. The required antenna size

__________ as the operating frequency of a system increases, assuming that antenna gain remains unchanged.

a. Remains the sameb. Increasesc. Decreasesd. All of the above

Questions17. A 20-m antenna gives a certain

up-link gain at frequencies of 4/6 GHz. For getting the same gain in 20/30 GHz band, antenna size requires __________ meters.a. 100b. 4c. 1d. 10

Questions18. Orbital disturbances of a geosynchronous satellite are caused by

a. Moonb. Sunc. Earthd. All of the above

Questions19. Geosynchronous satellites

a. Has the same period as that of the earth

b. Has a circular obitc. Rotates in the equatorial plane

d. All of the above

Questions20. To cover all inhabited regions of

the earth, the number of geosynchronous satellites required is

a. 5b. 10c. 2d. 3

Questions21. A geostationary satellite is one

whicha. Hangs motionless in space about 36,000 km above the earth

b. Travels around the earth about 24 hrs.

c. Remains stationary above the earthd. Appears stationary above the earth

Questions22. Geosynchronous Communication

satellites travel around the earth in circular orbits with forward speed of about __________km/hr.

a. 100,000b. 36,000c. 11,200d. 22,800

Questions23. The period of the satellite is

a. The amount of time it takes for a satellite to complete one orbit

b. The point on an orbit where satellite to complete one orbit

c. The time it takes the satellite to travel from perigee to apogee

d. An orbital arc that extends from 60 degrees west longitude to 145 degrees west longitude

Questions24. What is the satellite's period orbiting in a circular pattern with elevation of 1000 km?

a. 1 hr 45 minsb. 2 hrs 45 minsc. 2 hrs 30 minsd. 3 hrs

Questions25. A satellite, orbiting in a circular orbit,a. Has constant velocityb. Has varying velocityc. Is not moving at alld. Both a and b

Questions26. What is a descending pass for a satellite?

a. A pass from west to eastb. A pass from east to westc. A pass from south to northd. A pass from north to south

Questions27. Satellite rotating in an orbit takes it over the north and south poles is ina. Inclined orbitb. Polar orbitc. Equatorial orbitd. Declined orbit

Questions28. The farthest point a satellite can reach isa. Apogeeb. Perigeec. Altituded. Attitude

Questions29. Include all earth stations within line-of-sight path of a satellitea. Satellite shadowb. Earth shadowc. Zonald. Global

Questions30. The different multiple accesses

which permit many satellite users to operate in parallel through

a. A Single Transponder Without Interfering With Each other are

b. FDMAc. TDMAd. CDMAe. All of the above

Questions31. A digital technology that uses a low

power signal spread across a wide bandwidth. With this technology, a phone call is assigned a code instead of a certain frequency. Using identifying code and a low power signal, a large number of channels can used the entire bandwidtha. TDMAb. PCDMAc. PMAd. CDMA

Questions32. The use of the same frequency on the same geographical area

a. Frequency reuseb. Roamingc. Homingd. Cellular

Questions33. In selecting a satellite system, the first determining factor isa. Coverage areab. EIRPc. Antenna sized. Antenna gain

Questions34. The earth's area or region that the satellite can receive from or transmit toa. Footprintb. Skip zonec. Primary aread. Finger print

Questions35. Satellite radiation pattern that covers 1/3 of the earth's surface

a. Earthb. Zonalc. Spotd. Global

Questions36. A satellite position is measured by its _________ angle with respect to the horizon.a. Elevationb. Depressionc. Azimuthd. Incidence

Questions37. The _________ angle measures the satellite position clockwise from the direction of true North

a. Elevationb. Depressionc. Azimuthd. Incidence

Questions38. GPS has a total number satellites equal toa. 12b. 24c. 36d. 48

Questions39. How many elliptical orbits does Navstar GPS have?

a. 5b. 6c. 7d. 8

Questions40. What is the free space attenuation of a satellite system operating at 36,000 km above the earth operating at 5 GHz?a. 180 dBb. 190 dBc. 198 dBd. 189 dB

Questions41. The FDMA technique wherein voice band channels are assigned on “as needed" basis.a. PAMAb. DAMAc. SSMAd. CDMA

Questions42. A satellite equipped with electronic devices to receive, amplify, convert, and retransmit signals.

a. Passiveb. Activec. Uplinkd. Downlink

Questions43. An earth station transmits signal to

a satellite 38,500 km, directly overhead it. What is the propagation delay when the signal is received back at the same earth station, in milliseconds?a. 257b. 200c. 285d. 185

Questions44. A satellite communication link between

Pinugay Earth Station, Philippines and Mt. Fucino Earth Station, Italy is to be established. If the assigned uplink frequency at Pinugay Earth Station is 6175 MHz, what is the downlink frequency at Mt. Fucino Earth Station, in MHz?

a. 4545b. 3950c. 3789d. 4200

Questions45. "The orbit of any planet is an ellipse with the sun at one focus". This isa. Kepler's First Lawb. Kepler's Second Lawc. Kepler's Third Lawd. Law of universal Gravitation

Questions46. When a satellite orbits in the opposite direction as the earth's rotation with an angular velocity less than that of the earth

a. Orbitalb. Progradec. Retrograded. Geostationary

Questions47. The actual user information conveyed through the satellite systema. Bus transmissionb. Payloadc. Prograded. Retrograde

Questions48. The spatial separation between geosynchronous satellites

a. 1-3 degreesb. 3-6 degreesc. 6-8 degreesd. 8-10 degrees

Questions49. The footprint which covers a very small geographical area.a. Spot coverageb. Zonal coveragec. Earth coveraged. Regional coverage

Questions50. The satellite frequency reuse method

which sends different information signals using vertical or horizontal electromagnetic polarization

a. Multiple coverage areasb. Dual polarizationc. Spatial separationd. Spread spectrum

Questions51. __________ detects the satellite signal relayed from the feed and converts it to an electric current, amplifies and lower its frequency.a. Feedhornb. Satellite dishc. Satellite receiverd. LNA

Questions52. Satellites used for intercontinental

communications are known asa. Comsatb. Domsatc. Marisatd. Intelsat

Questions53. What is the basic function of a

communications satellite?a. To act as a receiving antenna for broadcast FM

b. To compensate for the antenna limitations

c. To eliminate aerodynamic dragd. To act as a receiving antenna for broadcast AM

Questions54. What do you call of a satellite used to provide satellite services within a single country?a. Orbital satelliteb. Geostationary satellitec. Non-synchronous satellited. Domestic satellite

Questions55. A satellite beam that covers almost 42.5% of the earth's surface.

a. Zone beamb. Hemispheric beamc. Spot beamd. Global beam

Questions56. The first Philippine satellite has how many channels?a. 30b. 24c. 48d. 50

Questions57. Aguila I has how many transponders?a. 36b. 48c. 24d. 12

Questions58. How many satellite orbital slots were requested by the Philippine Government from ITU?

a. 2b. 4c. 6d. 8

Questions59. The most common device used as an LNA isa. Zener diodeb. Tunnel diodec. IMPATT dioded. Shockley diode

Questions60. The radiation patterns of earth coverage antennas have a beamwidth of approximately

a. 21degreesb. 5 degreesc. 17 degreesd. 35 degrees

Questions61. The main power sources for satellites area. Batteriesb. Solar cellsc. Fuel cellsd. Thermoelectric generators

Questions62. What is the common up-converter and down-converter IF?

a. 36 MHzb. 40 MHzc. 70 MHzd. 500 MHz

Questions63. When the satellites are spaced 4 degrees of the 360 degrees complete circle, how many parking spaces or orbit slots are available?a. 90b. 85c. 95d. 80

Questions64. The first satellite launched for a geosynchronous orbit but unfortunately lost during orbit injection.

a. Syncom Ib. Telstar Ic. Sputnik Id. Early Bird

Questions65. Geostationary satellites are located _______ with respect to the equator.a. 0 deg longitudeb. 0 deg latitudec. 90 deg latituded. 45 deg latitude

Questions66. Incidentally proposed the geostationary scheme or orbit of satellites in 1940's.

a. Clarkeb. Gaussc. Morsed. Gray

Questions67. The control routine necessary to keep the satellite in position is referred to asa. Station keepingb. Station trackingc. Station monitoringd. Station maintenance

Questions68. A satellite which simply reflects the signal without further amplification.

a. Passiveb. Activec. Geostationaryd. Posigrade

Questions69. What is the line joining the ascending and descending nodes through the center of the earth?

a. Line of apsidesb. Line of nodesc. Line of shootd. Line of sight

Questions70. The line joining the perigee and apogee through the center of the earth.a. Line of sightb. Line of nodesc. Equatorial beltd. Line of apsides

kepler's law kepler’s first law – the orbit of any planet is an ellipse with the sun at one...

Documents

satellite functions

keplers law keplers

law law of areas

law law of periods

portion of satellite

output power

stable orbit

power supply