02 skyedge basic satellite

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Satellite CommunicationsFundamentals


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Other Advantages of Satellite Communications:• Ideal for point-to-multipoint and large distributed networks

• Asymmetrical bandwidth

• Easier traffic analysis due to single point of management

• Low BER (typically less than 10-8)

• Simultaneous delivery of data to unlimited number of stations

• Independence from PTTs

• Private Network

Why Satellite Communications ?

Huge Geographical Coverage

No ‘line-of-site’ problems

Extremely reliable (99.9% Up time)

Reliable data broadcast or multicast

Single Vendor

Easy to deploy

Supports multiple applications:

Video

DataVoice


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Dial-Up:

• Dependant on local PTT(s) and infrastructure

• Costly

• No broadcast/multicast possibility

• Only Symmetrical data speeds possible

RF/Microwave Links:

• Limited by line of site path

• Entire signal path close to Earth’s surface

• Potential for high levels of signal degradation due to atmosphere & precipitation

• Distance dependant: Theoretical maximum distance between repeaters is only 40-60Km

•Complicated, expensive, time consuming implementation

Fiber Optics/Leased Lines:

• Very Expensive to implement and maintain

• Not available everywhere

• Not feasible/economical for low bit rate remote sites

Microwave

MMDS

LMDS

Wireless LANs

Fiber Optics

ADSLCable Modems

POTS- Dial-up

Alternatives to SatelliteCommunicationsDial-Up/Fiber Optics/RF Links


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Alternatives to Satellite Communications

RF (Microwave) Links:

Two geographically separated sites can be connected by a microwave link. However thedistance over which the link will work depends very much on the frequency used. Forexample, C-Band (6/4 GHz) will propagate much further that the Ka-band (20/30 GHz).

Where the sites to be connected are further apart than physics allow (due to path loss,curvature of the Earth, rain-fade, etc.) a ‘mid-point’ can be used as a ‘rebroadcast’ site.

Typical link distance, per hop, at 15 GHz is between 30 and 50 km. The biggest difficultyis often engineering sufficient margin for rain fade. With typical attenuation of 0.2db/kmfor average rain fall, over a 50 km link, this equates to 10db of attenuation (assumingrainfall across the entire link).

In a satellite link, rain fade also exists, however attenuation is relatively low due to thefact that compared to microwave links which follow a terrestrial path, rain fall between

the ground station and the satellite is often less than several kilometers.For broadcast applications, microwave works well over small areas. Satellite bycomparison offers coverage of cities and continents from a single transmitter. Power isprovided via the solar panels ‘free’ for the entire lifetime of the satellite.

ISDN:

ISDN (Integrated Services Digital Network) is a set of CCITT/ITU standards for digitaltransmission over ordinary telephone copper wire as well as over other media. Homeand business users who install an ISDN adapter (in place of a modem) can up toconnect at bit rates up to 128 Kbps. ISDN requires adapters at both ends of thetransmission so your access provider also needs an ISDN adapter. ISDN is generallyavailable from your phone company in most urban areas in the United States andEurope. There are two levels of service: the Basic Rate Interface (BRI), intended for thehome and small enterprise, and the Primary Rate Interface (PRI), for larger users. Bothrates include a number of B-channels and a D-channels. Each B-channel carries data,voice, and other services. Each D-channel carries control and signaling information.

The Basic Rate Interface consists of two 64 Kbps B-channels and one 16 Kbps D-channel. Thus, a Basic Rate user can have up to 128 Kbps service. The Primary Rateconsists of 23 B-channels and one 64 Kpbs D-channel in the United States or 30 B-channels and 1 D-channel in Europe.

Integrated Services Digital Network in concept is the integration of both analog or voicedata together with digital data over the same network. Although the ISDN you can installis integrating these on a medium designed for analog transmission, broadband ISDN(BISDN) will extend the integration of both services throughout the rest of the end-to-end

path using fiber optic and radio media. Broadband ISDN will encompass frame relayservice for high-speed data that can be sent in large bursts, the Fiber Distributed-DataInterface (FDDI), and the Synchronous Optical


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Alternatives to Satellite Communications (cont.)

Network (SONET). BISDN will support transmission from 2 Mbps up to much higher, butas yet unspecified, rates.

ISDN, developed in the early 80’s and and implemented mainly over the past severalyears, is being replaced by-in-large by DSL modems.

DSL Technology:

DSL (Digital Subscriber Line) is a technology which allows delivery of broadband dataover ordinary copper telephone lines. The main limitation of this DSL is the proximity tothe central telephone office. xDSL refers to different variations of DSL, such as ADSL,HDSL, and RADSL. Assuming your location is close enough to a telephone companycentral office that offers DSL service, you may be able to receive data at rates up to 6.1megabits (millions of bits) per second (of a theoretical 8.448 megabits per second),

enabling continuous transmission of motion video, audio, and even 3-D effects. Moretypically, individual connections will provide from 1.544 Mbpss to 512 Kbps downstreamand about 128 Kbps upstream. A DSL line can carry both data and voice signals and thedata part of the line is continuously connected. DSL is expected to replace ISDN inmany areas and to compete with the cable modems.


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Alternatives to Satellite Communications (Cont.)

Cable Modems:

A cable modem is a device that enables you to hook up your PC to a local cable TV lineand receive data at about 1.5 Mbps. This data rate far exceeds that of the prevalent 28.8and 56 Kbps telephone modems and the up to 128 Kbps of Integrated Services DigitalNetwork (ISDN) and is about the data rate available to subscribers of Digital SubscriberLine (DSL) telephone service. A cable modem can be added to or integrated with a set-top box that provides your TV set with channels for Internet access. In most cases, cablemodems are furnished as part of the cable access service and are not purchaseddirectly and installed by the subscriber. This service is not available on all cablenetworks.

A cable modem has two connections: one to the cable wall outlet and the other to a PCor to a set-top box for a TV set. Although a cable modem performs modulation betweenanalog and digital signals, it is a much more complex device than a telephone modem. Itcan be an external device or it can be integrated within a computer or set-top box.

Typically, the cable modem attaches to a standard 10BASE-T Ethernet card in thecomputer.

LMDS:

LMDS (Local Multipoint Distribution Service) is a wireless technology which is capable oftransmitting a large amounts of data at a very high bitrate using microwave radios. Onemicrowave radio is installed on a building at the client site and another microwave radiois installed at the LMDS base station. Communication between the client and servermust be line-of-site. The network can be constructed in a point to point or point tomultipoint fashion.

LMDS operates in the 20-30 GHz Ka band, thus the antennas are very small, directionaland offer high gain. The spectrum is auctioned by the government in the US for LMDSuse. Range is limited due to power limitations, line-of-site propagation andattenuation due to rain.

LMDS Remote Antenna/Transceiver LMDS Hub Antenna/Transceiver


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VSAT – Very Small Aperture Terminal

Bandwidth

Frequency

Bitrate

Space Segment

Uplink

Downlink

Outbound

Inbound

Spectrum Analyzer

Basic Satellite FundamentalsDefinition of Terms

dB – Decibel

Gain

Attenuation

EIRP (Effective Isotropic RadiatedPower)

C/N (Carrier/Noise)

Eb/N0 - Energy (in bits)/Noise

BER – Bit Error Ratio

Link Budget/Link Margin

Transponder

Footprint

VSAT (VERY SMALL APERTURE TERMINAL): Earth station satellite antenna with a diameter or cross-section

dimension in the general range of 1.2 to 2.4 meters.UPLINK: The path that the transmission takes between the Earth Stations and the satellite

DOWNLINK: The path that the transmission takes between the satellite and the Earth Stations

OUTBOUND: The transmission path between the hub (through the satellite) to the VSATs

INBOUND: The transmission path between the VSATs (through the satellite) to the hub

SPECTRUM ANALYZER: A test and measurement device used to measure signals and noise within the frequencyspectrum. Used in VSAT installation to point antenna accurately towards the satellite.

RF (RADIO FREQUENCY): Any frequency within the electromagnetic spectrum normally associated with radiowave propagation.Organizations such as the FCC and ITU have divided the radio frequency spectrum intosubdivisions for management purposes.

dB (DECIBEL): An analog unit of measure of signal strength, volume, or signal loss due to resistance as expressedin logarithmic form.

GAIN: The ratio of output current, voltage or power to input current, voltage or power, respectively. Gain is usuallyexpressed in dB. If the ratio is less than unity, the gain expressed in dB, will be negative, in which case there is aloss between input and output.

ATTENUATION: The loss of power of electomagnetic signals between transmission and reception points.

C/N: Carrier over Noise Ratio – The Delta measured on the Spectrum Analyzer between the measured peak of thecarrier signal and the noise floor. Used for measuring an unmodulated signal.

Eb/N0: Energy (bits) over Noise- used as a means of measuring a digitally modulated signal. Provides a moreaccurate reference than C/N readings.


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BER: Bit Error Ratio - The number of erroneous bits divided by the total number of bits transmitted,received, or processed over some stipulated period.

LINK BUDGET/LINK MARGIN: A calculation which takes into account all the losses (attenuation) andgains (amplification) of a communications system relative to what is required to maintain effective,error free communications. The Link Margin is the difference between the minimal signal necessaryto maintain effective communications and the calculated stronger signal. This difference is calculatedto account for worst case scenarios such as rain fade, antenna mispointing, reduced satelliteperformance due to aging and equinox attenuation.

BANDWIDTH: A measure of radio frequency (RF) use or capacity. A terrestrial broadcast televisionchannel, for example occupies a RF bandwidth of 6 MHz or six million cycles per second while atelephone voice transmission requires a RF bandwidth of only 3 KHz or 3,000 cycles per second.

FREQUENCY: For a periodic function, the number of cycles or events per unit time.

BIT RATE: The amount of data being transported, measured relative to quantity over time in bits persecond (thousand bits per second or Kb/s, million bits per second or Mb/s or billion bits per second orGb/s) Summary of bitrate notations:

Bit: 100

(1 bit)Kilobit: 103 (1,000 bits)

Megabit: 106(1,000,000 bits)

Gigibit: 109 (1,000,000,000 bits)

Terabit: 1012 (1,000,000,000,000 bits)

C-BAND/Ku-BAND/Ka-BAND: Bands within the frequency spectrum used for satellitecommunications.

TRANSPONDER: A combination receiving and transmitting antenna on a communications satellite. Afrequency converter is also including in the transmit/receive package which converts the uplinkedsignal frequency to a transmission or downlink frequency.

FOOTPRINT: The area of coverage that a satellite is able to ‘see’. Measured in dBW, the satellite’sfootprint is illustrated in a contour map style, with each contour listing what level dBW is receivedwithin it’s area.

SPACE SEGMENT: Bandwidth leased from the satellite operator. Space segment consists of anOutbound Region and an Inbound Region, where the Inbound Region is usually shared using a Multi-Access, contention based scheme such as TDMA, FDMA or a combination of both.

EIRP (EFFECTIVE ISOTROPIC RADIATED POWER): The arithmetic product (expressed as dBW)of, (a) the power supplied to an antenna and (b) its gain.

AZIMUTH: Azimuth is an important consideration in locating a satellite for transmission or reception ofRF signals. The azimuth expressed in degrees of a circle will be the horizontal angle of rotation thatthe ground antenna must be rotated though to point at the specific satellite. Azimuth angles for anysatellite may be calculated given the latitude and longitude of the ground station and the location ofthe satellite in geosynchronous orbit relative to true north.

FEC (FORWARD ERROR CORRECTION): A technique which employs special codes that allow thereceiver to detect and correct a limited number of errors without referring to the transmitter.

GEO (GEOSYNCHRONOUS EARTH ORBIT): This is the orbital altitude of 35,580 km (22,237 miles)above the earth's surface where a satellite's velocity matches with the rotation of the earth. A satellitewhich is in a GEO position above the earth's equator (geostationary) will appear from the earth to beoccupying a stationary position. The geosynchronous earth orbit is also referred to as the ClarkeOrbit.


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dB Calculation Hints…

Here's some easily remembered factors for any "power" level, be it dBm or dBW:

+3 dB = [(x) (watts)] multiplied by 2-3 dB = [(x) (watts)] divided by 2

Then, of course:

+6 dB = [(x) (watts)] multiplied by 4-6 dB = [(x) (watts)] divided by 4

Knowing that positive and negative dB numbers are multiplication and division factorsrespectively, we can say the following:

+ or - 10 dB = mult or divide by a factor of 10



so,

+ or - 60 dB = mult or divide by a factor of 1,000,000

and further...

66 dBW (referenced to one watt) = 4,000,000 watts, or +60 db (1,000,000X) + 6 db (4X) =4,000,000 W.

and further more...

-30 dBm (referenced to 1 millwatt) = 1/1,000 of a milliwatt, which is 1/1,000,000 of a watt.


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Satellite Frequencies:

Satellite Frequencies

C-BandExtended C-Band

Ku-Band

Ka-Band

High Equipment

cost; attenuation

due to rain

17.7-21.727.5-30.5Ka

Attenuation due to

rain

11.7-12.214-14.5Ku

Shared withterrestrial

3.7-4.25.925-6.425C

Shared with ISM

Band

1.610-1.6252.483-2.5S

Shared with

terrestrial

.9-1.6.9-1.6L

NotesDown-Link (GHz)Up-Link

(GHz)

Band


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Types of Orbits

There are 4 main types of

Orbits that nearly all

satellites are located in:

LEO – Low Earth Orbit

MEO* – Medium Earth Orbit

GEO – Geosynchronous Orbit

HEO* – High Elliptical Orbit

*HEO and MEO Orbits are not commonly used for communications satellites and therefore will not

be covered as part of this chapter.

To learn more about HEO Satellites, link here:http://www.fas.org/spp/guide/russia/comm/elliptical/molniya.htm

To learn more about MEO Satellites, link here:http://www.ico.com


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Satellites in Low Earth Orbit (LEO)

The satellite must attain a speed of 17,000 mph (27,200 kmph) in a low orbit over the Earth’ssurface (this is also known as an inclined orbit since the satellite must pass over the equator twiceduring every revolution around the Earth.Characteristics:Smaller, less powerful rockets are required to place a LEO satellite into orbit as opposed to a GEOsatellite. The LEO satellite is moving relative to the Earth therefore communications is not practicalunless there is a “constellation” of satellites. The orbit for LEOs is about 125-875 miles (200-1400kms) above the Earth. These types of satellites are small (From < 1m sq.) and light in weight,allowing several to be launched in a single payload.

Types of Low Earth Orbit Satellite Systems:

Types of OrbitsLow Earth Orbit (LEO)

200-1400 Km above the Earth

Approximately 90 MinutePeriod

A single satellite in LEO orbit is‘In View’ for approximately 20minutes from AOS to LOS

Light, small, easy to launch,inexpensive

Minimal delay

Ideal for Telephony

Short life span as comparedwith GEO Satellites

Must work in a Constellation tobe effective

20-30 GHz1-3 GHz


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Globalstar is a consortium of leading international telecommunications companies originally

established in 1991 to deliver satellite telephony services through a network of exclusive serviceproviders. The Globalstar system is designed to provide high quality satellite-based telephonyservices to a broad range of users:

• Cellular users who roam outside of coverage areas• People who work in remote areas where terrestrial systems do not exist• Residents of under-served markets who can use Globalstar's fixed-site phones to satisfytheir needs for basic telephony• International travelers who need to keep in constant touch

Types of OrbitsLEO Constellation Satellite Networks - Globalstar

Loral initiativeSubsidiary of Airtouch (Cellular)

Aimed at global cellular phone coverage

Qualcomm based CDMA

48 satellite constellation (8 planes x 6 ea.+ 4 spares)

52 now in orbit !

8 orbital planes of 6 satellites each

80% Earth coverage (+/- 68 degrees)

LEO orbit (1414 km)

Ground Operations Control Centers(GOCCs) and Satellite Operations ControlCenters (SOCCs) control gateway andcontrol functions

Qualcomm GSP1600 Erricson R290 Telit SAT 550

To find out more about Globalstar, link here: http://www.globalstar.com


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Types of OrbitsLEO Constellation Satellite Networks - Teledesic

Original plan for 840 Satellites

Later redesigned for 288 (12 planes of 24Satellites) – Not including spares

Aimed mainly at an “Internet in the Sky” Networkbut can support PSTN’s and Enterprise Networks

2 Mbps IB/64 Mbps OB; Ka Band

1375 Km altitude (Still LEO)

Service not to begin until 2005

Partners: Craig McCaw (Teledesic CEO),Bill Gates, Boeing, His Royal HighnessPrince Alwaleed Bin Talal Bin Abdul AzizAlsaud, His Royal Highness PrinceAlwaleed Bin Talal Bin Abdul Aziz Alsaud

$9b estimated investment !

Teledesic is in it’s planning phase and is not scheduled to go on line until 2005.

Teledesic is building a global, broadband Internet-in-the-SkyTM network. Teledesic plans toprovide broadband Internet access, interactive multimedia and high-quality voice. Teledesic is aprivate company based in Bellevue, Wash., a suburb of Seattle. Teledesic will operate in thehigh-frequency Ka-band of the radio spectrum (28.6-29.1 GHz uplink and 18.8-19.3 GHzdownlink).


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Teledesic's space-based network uses fast-packet switching. Communications are treated withinthe network as streams of short, fixed-length packets. Each packet contains a header that includesdestination address and sequence information, an error-control section used to verify the integrity

of the header, and a payload section that carries the digitally encoded user data (voice, video,data, etc.). Conversion to and from the packet format takes place in the terminals at the edge ofthe network.

The topology of a LEO-based network is dynamic. The network must continually adapt to thesechanging conditions to achieve the optimal (least-delay) connections between terminals. TheTeledesic Network uses a combination of destination-based packet addressing and a distributed,adaptive packet routing algorithm to achieve low delay and low delay variability across thenetwork. Each packet carries the network address of the destination terminal, and each nodeindependently selects the least-delay route to that destination. Packets of the same session mayfollow different paths through the network. (See Figure Above) The terminal at the destinationbuffers and if necessary reorders the received packets to eliminate the effect of timing variations.The channel resources associated with a cell are shared among terminals in that cell, withcapacity assigned on demand to meet their current needs. This flexibility allows Teledesic to

efficiently handle a wide variety of user needs: from occasional use to full-time use; from burstyto constant bit-rate applications; from low-rate to high-rate data; from low usage-density areas toareas of relatively high usage density.A multiple access scheme implemented within the terminals and the satellite serving the cellmanages the sharing of channel resources among terminals. Within a cell, channel sharing isaccomplished with a combination of Multi-Frequency Time Division Multiple Access (MF-TDMA) on the uplink and Asynchronous Time Division Multiplexing Access (ATDMA) on thedownlink.

To find out more about Teledesic, link here: http://www.teledesic.com/tech/tech.htm

For the latest update of Teledesic and other LEO Constellation Networks, click here:

http://www.ee.surrey.ac.uk/Personal/L.Wood/constellations/teledesic.html


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Types of OrbitsLEO Constellation Satellite Networks - Iridium

Original plan for 77 Satellites

Later redesigned for 66 not includingspares in 6 Orbital planes

Orbital Height: 780 Km

Orbital period: 100 minutes, 28 seconds

Spot Beams: 48 per satellite

Each 48 km in diameter

Satellite Expected Lifetime: 7-9 Years

Filed for Chapter 11 in 1999, restructured in 2001

http://www.iridium.com/ for more details

Iridium was originally planned to have 77 active satellites, and named after the

element with 77 electrons (count the electron shells to get 77 when the atom is not bonded. Iridium alsohas an atomic number of 77 resulting from its 77 protons; the idea of electrons orbiting the nucleus beinganalogous to satellites orbiting the earth is tenuous, thanks to Heisenberg's uncertainty principle.)Iridium was later redesigned to need fewer satellites - the 66 active satellites of today. (We're not countingin-orbit or ground spares.) But its name hasn't been changed to Dysprosium, the element with 66 protonsand often 66 surrounding electrons whose Latin root means 'bad approach'...Motorola's own webpages, created back when Iridium satellites were planned to have six, rather than four,intersatellite links, have technical information that supplements what you'll find on the many officialwebsites.Iridium LLC filed with the FCC for the followup project - a 96-satellite system called MacroCell . This wouldhave competed with Globalstar's GS-2 system of 64 satellites - if they got built. MacroCell might be going

by the name Iridium Next or INX these days, but you're unlikely to see it mentioned anywhere outside oldFCC filings.An Iridium satellite has been donated to the Smithsonian Air and Space Museum in Washington DC. It wasapparently hung outside their Star Wars exhibit a long, long time ago, but now hangs in the aptly-namedBeyond the Limits gallery.Handheld units use L-Band uplinks (1616-1626.5 MHz) Inter-satellite and groundstation links use Ka-Band.Secure Handheld units are being sold and marketed by General Dynamics:http://www.gd-decisionsystems.com/space/products/mwins/


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Types of OrbitsLEO Constellation Satellite Networks - Orbcomm

36 Satellites in 6 Orbital Planes

Altitude 825 Kms

Global Data and Messaging

Aimed at Mobile Data Comm Market

Supports MultiCast services

Low Bit Rates (2.4/4.8 Kbps)

VHF/UHF Up/Downlinks

http://www.orbcomm.com/home.htm or

http://www.orbcomm.co.kr/english/e_our/index-2.htm for more details

ORBCOMM: The world’s first commercial global wireless data and messaging system. The ORBCOMM

System uses low-Earth orbit (LEO) satellites to provide cost-effective tracking, monitoring and messagingcapabilities to and from anywhere in the world. Similar to two-way paging or e-mail, the system is capableof sending and receiving two-way alphanumeric packets of data. These short, economical messagesincrease the efficiency of your remote operations by making critical information readily available, oftenfrom areas beyond the geographic and economic reach of traditional systems.


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Types of OrbitsMEO Constellation Satellite Networks - ICO

12 Satellites in 2 Orbital Planes

Altitude: 10,390 Km

Filed for Chapter 11 in 1999. Emerged in 2000

http://www.ico.com/ for more details

ICO (for Intermediate Circular Orbit , another term for Medium Earth Orbit - Middle Earth has already been

taken by Tolkien) was originally begun by Inmarsat as Project 21, then Inmarsat-P , before being spun offinto a separate company just as all the other schemes have been. As an international treaty organisationwhich countries join, Inmarsat has held a lot of clout (and still does now it's transitioning to a normalprivatised company), and it already offers a limited telephone service from GEO (which e.g. NERA willhappily sell you a quite expensive terminal for). And since ICO is slow off the mark, that bulky telephoneservice has been improved to give Mini-M in the interim. Nera is also planning ICO handsets - a satellitestandby time of over 120 hours, apparently...ICO may only be bent-pipe transponders with digital signal processing at MEO, but Inmarsat is one of thefew companies to already have a successful track record in operating satellite phones - from bent-pipetransponders at GEO. The service is decided by the equipment on the ground, which has allowed ICO tomove to encompass data applications.


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The satellite must travel over the equator through space in the same direction the earth rotates(West to East). The satellite must take exactly the same time to orbit the Earth as the Earthitself takes to rotate (23 hrs, 56 minutes) - ~15 degrees per hour. When this occurs, thesatellite appears to be stationary with respect to any location on the Earth.

Characteristics.

GEOs do not have to tracked; they maintain the same relative position, although they have tobe monitored for station keeping. Theoretically, a single Geosynchronous satellite can coverapproximately 42% of the globe. A system of 3 satellites provides nearly worldwide coverage.In practice, the satellites steer their beams to smaller areas to provide higher gain overpopulated areas.

• High cost: about $250 million to get the satellite in orbit ($100 - 200 million tobuild, $75 - 100 million to launch). The probability of getting the

satellite successfully into orbit is 85 - 90%.• Lifetime. The lifetime of a GEO has increased from the original 3 - 4 years to the present15 - 25 years.

Arthur C. Clarke.

This eminent science fiction writer is credited with conceiving the application of communicationsatellites. His article on extraterrestrial relays in Wireless World magazine in 1945 specificallydescribed a three satellite worldwide network. Clarke also wrote the famous novel - “2001: ASpace Odyssey”

35,680

Km.

The Clarke Belt

Types of OrbitsGeosynchronous Orbit (GEO)

35,680 Km above the Earth

~24 Hour Period

Average 14-17 Year Lifespan

Single Satellite provides up to42% Earth Coverage

Large, expensive, difficult tolaunch

Located approximately every 2

above the equatorSeveral Satellites may operateat the same azimuth ondifferentfrequencies/polarization


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Eutelsat Fleet

EUTELSAT's fleet of 19 satellites ranks as one of the largest globally. In addition to TV andradio broadcasts, EUTELSAT pioneered the delivery of Internet backbone, push and cacheservices in Europe, and provides capacity for corporate networks, satellite newsgathering,telephony, and mobile voice, data and positioning services. The fleet comprises several satellitefamilies. The members of each family typically share a common mission (e.g. to provide TVbroadcasting or telecommunications services) and similarities in their design and construction.

Types of OrbitsGeosynchronous Orbit (GEO) Fleets - Eutelsat


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Intelsat 707 @ 359 degrees East - Key Parameters

Total Number of Transponders:C-Band:42 (in equiv. 36 MHz units) Ku-Band:28 (in equiv. 36 MHz units)

Polarization:

C-Band:Circular – Right Hand or Left Hand, Ku-Band:Linear – Horizontal or Vertical

e.i.r.p. (C-Band):(Beam Edge to Beam Peak)Global Beam:26.0 up to 34.1 dBW Hemi Beam:32.3 up to 40.4dBWZone Beam:32.3 up to 40.9 dBW

Uplink Frequency:

C-Band:5925 to 6425 MHzKu-Band:14.00 to 14.50 GHz

Downlink Frequency:

C-Band:3700 to 4200 MHzKu-Band:10.95 to 11.20 GHz or11.70 to 11.95 GHz or12.50 to 12.75

GHz plus11.45 to 11.70 GHzG/T (C-Band)- Gain/(Noise)Temperature [A characteristic of an antenna’s performance):

(Beam Edge to Beam Peak)Global Beam:-12.0 up to -7.2 dB/KHemi Beam:-8.7 up to -1.6dB/KZone Beam:-9.2 up to +1.0 dB/KC-Spot Beam:-5.0 up to +2.9 dB/K

G/T (Ku-Band):(Beam Peak) Spot 1:Up to +9.6 dB/KSpot 2:Up to +6.3 dB/KSpot 3:Up to +7.2 dB/K

SFD Range:[Saturation Flux Density -- power required to achieve saturation of a singlerepeater channel on the satellite.](Beam Edge)C-Band:-87.0 to -73.0 dBW/m² Ku-Band:-87.0 to-73.0 dBW/m²

(Link here http://www.lyngsat.com/i707.shtml to see who’s on this Satellite)

Types of OrbitsGeosynchronous Orbit – Intelsat 707 – Key Parameters

INTELSAT 707 @ 359.0°ESatellite Coverage Map and Key Parameters

Hemi Zone Ku-Spot C-Spot


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Footprint provides a picture of the signal that is received at a location in the country with respect towhat Effective Isotropic Radiated Power (EIRP) is from the satellite.

This picture gives us a good idea of what areas of the country receive the lowest level signals andwhat areas receive the highest signals.

EIRP (EFFECTIVE ISOTROPIC RADIATED POWER): The arithmetic product (expressed as dBW)of, (a) the power supplied to an antenna and (b) its gain.

Beam Shaping. This is a powerful technique for increasing the effectiveness of a satellite. Forexample a single elliptical beam is compared with a shaped-beam coverage from combining threenearly circular beams. The single elliptical beam radiates about half its energy outside the landmass.

Satellite Footprints

Three types of Beams:

Hemi

Zone

Spot

“Shaped” using phased arrayantennas


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Launch OptionsSea Launch

Floating Launch site sits on theequator 230 Km from ChristmasIs.

Multinational project involvingBoeing, Norway's KvaernerGroup, Russia's Energiyaspacecraft builder andUkraine's Yuzhnoye rocketcompany

Significant savings overconventional launch

6000 kg lift capability

Launch to all inclinations froma single site

8 Successful launches since3/99

The Earth is not a perfect sphere but rather more egg shaped. The Circumference of the Earthfrom North to South is approximately 26,400 miles (42,240 km’s) while the circumference from

East to West is slightly less – approximately 25,046 miles (40,074 km’s).

If it was possible to shut off gravity, a person standing on the equator would fly off the Earth’s

surface at approximately 1044 mph (1670 kph). Satellite Launch vehicles take advantage of this

‘free’ boost when launched from on, or near the equator in a west to east direction. This kind of

launch saves fuel, allowing more weight to be placed in the payload and less on wasted fuel.

Launch Systems:

Ariane - Owned by European Space Agency. Launch facility

in Kourou, French Guiana -- just 5o north of the equator.

Space Shuttle - Very expensive. Scheduling problems.

Delta - Benchmark for reliability with government andcommercial launches every few weeks.

Used for Iridium Project. Approaching 9000 lb payload

Boeing Sea Launch - Formed in 1995, uses converted

oil platform, can locate to optimum launch site.

Proton - Russian launch vehicle - most powerful.

Capable of hauling more than 10,000 lbs into GEO orbit.

ESA Arian Launch Vehicle


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Launch OptionsSingle Vs. Ariane Launch Vehicle

Enlarged

Fairing

Spacecraft

Spacecraft

NormalFairing

Spacecraft

Single Ariane

Payload

Attach

Fitting

Perigee Kick

Stage (PAM*)

Separation

Ring

Dual Launch

Structural

Casing

* PAM = Payload

Assist Module

The graphic presents, in simplified form, the physical interface for two typical expendableLVs. The fairing is the outer shell of the LV which contains the spacecraft constraining itsheight and width.

In the Ariane, one spacecraft is mounted on top of a structural casing within which thesecond spacecraft is contained. Once in transfer orbit, the spacecraft are sequentiallyreleased for subsequent injection into GEO by their respective Apogee Kick Motors (AKM).

Ariane uses an enlarged three-meter diameter fairing which makes possible the launch ofrelatively large spacecraft.


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1

2

3

7

8

LaunchSequence of Events

Launch – Sequence of Events

1. Liftoff. Delivers the vehicle to a 100 - 200 mile high orbit.

2. Parking orbit. A circular orbit (may stay here for 2 -4 orbits).

3. Perigee Kick. Occurs about 200 miles out and places the vehicle in a geostationary transferorbit (GTO).

4. TT&C line established with ground.

5. Reorientation to Apogee Motor Firing (AMF) attitude.

6. Preburn Reaction Control System (RCS) maneuvering.

7. Apogee Kick. Occurs about 22,300 miles out and pushes the satellite into GEO orbit (20 -30% of failures occur here).

8. Orbital adjustments.

9. Drift to assigned station in Clarke Belt (Geosynchronous orbit ring).

10. Orbit and attitude adjustment.

11. De-spin of platform.

12. Spacecraft deployments.

13. Bus testing.

14. Payload testing.

15. Start operations.


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Station Keeping

64 Km

64 Km

Achievement of a GEO orbit with the satellite at its assigned longitude usually starts theoperational phase. This, however, marks the beginning of a continuous tug of war with naturalphysical elements of nature. If the Earth were the only source of gravitational pull, and its masscould be represented by a sphere of uniform density, then the satellite would stay in itslongitude station indefinitely. The real situation differs on both counts, however, as describedhere and on the next page.

Adverse Forces. The various elements of nature, which are acting adversely on theGeosynchronous orbit and longitudinal station are generated by the Earth, Sun, and the Moon.These forces are described on the next page.

Objective. The fundamental objective is to maintain a specific longitudinal location of thesatellite over the equator with a maximum variation of +/- 20 miles (32 Kms). As seen from theEarth’s surface, this appears to be a box about 40 miles square (64 Kms) or 0.05º per side.

Consequences. The consequences of a failing to maintain station will require the retraining ofthe ground antenna (10 to 20 meters for C-Band and 8 to 10 meters for Ku-Band) and will leadto interference with other satellites in their “boxes”.


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Gravitational Effects on theSatellite

Sun

Gs

Ps

Gm

The effects on the position of the satellite come from three major sources; the Earth, the Sun

and the Moon.Earth Effect.

The fact that the Earth’s center of gravity is not in the center, is constantly changing, and thatthe Earth is not perfectly “round”, all contribute to the fact that the Earth “wobbles” on its axis.This all results in a non-uniform force exerted on the satellite -- dependent upon the satellite’smomentary relative position to the Earth.

Sun and Moon Effects.

The molecular energy of the light and heat generated by the Sun produces a pushing effect thatover time will cause the satellite to move outside of its 40 mile square station keeping box. Thepressure is about two millionths of a pound per square foot.

In addition, the satellite must contend with the gravitational pull of the Sun and Moon. Thesetend to make the orbit inclined -- increasing approximately one degree per year.

End Result. To an observer on the Earth, the major effect from all the natural effects is -- thesatellite appears to move between a North and South location in reference to the Earth’sequator during each daily 24 hour period (see next page).


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Drift Pattern

64 Km

64 Km

Equator

6 Weeks

Corrections

Applied

6 Weeks

The effects of the Earth, Sun, and Moon combine to gradually shift the satellite out of thedesired orbit and outside of the 40 mile (64 km) box.

Inclination Effect. The gravitational pull from the Sun and Moon, as mentioned, impart aninclination to the orbit. For a given inclination, say 0.1 degrees, the satellite will appear belowthe equator at one point in time and then above the equator precisely 12 hours later.

As the position error is developed over time, the error is seen as a 24 hour sinusoid thatappears in a figure “8” pattern.

Correction. About every 6 weeks, a North-South correction is made to the satellite position andthe alternately, on a different 6 week schedule, an East-West correction is made. The wholepurpose of this exercise is so that the ground antennas do not have to move.

The periodic corrections are called, “moving to the Center-of-the-Box”.

These maneuvers are performed by the Tracking, Telemetry, and Command (TT&C) stations.

The spacecraft antenna direction can be adjusted north or south over the 24-hour period tooptimize communication performance in spite of the instantaneous position of the satellite.


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Thrusters

Rotating

Motion

Linear

Motion

When the satellite has drifted from the nominal assigned position, a signal is sent to it over theCommand Channel to initiate turning on the appropriate thrusters to maneuver the satellite.

Thrusters.

The thrusters are small rocket motors that typically use Hydrazine as a fuel. These thrustersare located geometrically on the satellite so that the satellite can be maneuvered in anydirection or motion required to reorient the satellite. The thrusters are ignited in pairs in orderto provide a force that moves about the center of the space craft. See the graphic.

The typical satellite has 16 thrusters.

Commands.

All commands are initiated from the Satellite Control Center and are sent to the satellite from

one of the TT&C stations.Because the satellite is in free space and weightless, it takes very little energy or fuel to movethe satellite.


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Thermal Control

Face

X

Y

Z

The Face Points ...

E & W along the Equator

N & S (Solar Arrays attached)

Towards (and away) from Earth

Remarks

Metalized Blankets

Tile Mirrors

Metalized Blankets

Y

Z

X

Thermal Control of the satellite is necessary to protect the electronics that are used for thecommunications and controls.

The electrical and mechanical devices used in the satellite generate excess heat which mustbe removed and the external heat and cold must be controlled.

The sides that receive sunlight must have insulation to keep the radiated heat from over-heating the systems and the sides facing away from the Sun must keep the extreme cold fromcooling the systems too much.

Passive Thermal Control. This control consists of metal blankets, and mirrored tiles. Theblankets provide a high gloss finish that reflect most of the Sun’s heat away. They also preventheat from escaping the interior. The tiles also reflect the Sun, but allow the interior heat toescape.

Active Thermal Control. This control is provided by two systems:Internal Heaters - for use during Solar eclipses (which last about 70 minutes). They areactivated by the Tracking, Telemetry, and Command (TT&C) station on the ground and arepowered by the batteries.

Refrigerant Cooling Equipment - used to carry away the heat generated by the Sun andalso the High Power Amplifiers (HPA).


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Source: Sun’s Energy captured by Solar Panels

Efficiency: 10%

Maximum Capacity: 130%

Flat surface of the Arrays always pointed to the Sun

Sun’s Energy is converted to DC Power

Captured Electrical Energy serves several purposes

Electrical Power Generation

Satellites use solar arrays that have hundreds of solar cells mounted on the solar array panels.These panels are mounted to axial drive motors located on the Y faces which allow them to bepositioned so that they are pointed toward the Sun.

Capacity. Solar cells have life expectancy in excess of the satellite’s life, however solar dustdestroys about 3% per year. Consequently the satellite starts with about 130% capacity andmust regulate the power it uses.

How Sun’s Energy is Used. The Sun’s energy is used to charge the bank of batteries, andprovide power to the:

Communications Equipment

Drive motor assemblies

Three axis stable platform

Rotation. The satellite has Sun sensors onboard, so that the location of the Sun with respectto the satellite’s orientation is always known. This information is used to control the axial drivemotors for the Solar Arrays in order to keep the flat surface of the arrays pointed toward theSun.

The Solar Arrays rotate at the same rate which the satellite is rotated for the Earth pointingoperation, but in the opposite direction.


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Batteries

Autumn

Equinox

Spring

Equinox

Sun

The Solar Eclipse periods vary during the year as we go through the periods of AutumnEquinox (Sep/Oct) and the Spring Equinox (Mar/Apr).

Equinox Effect. At the peak of the two equinox periods, the satellite is shaded from the Sun bythe Earth for as long as 70 minutes as it passes through the 8000 mile (12,800 km) wideshadow. The equinox periods are about 20 days long from when the first shading occurs untilthe last occurs.

During these shading periods, the satellite must still operate. Therefore all electrical powerrequirements on the satellite are provided by the backup battery bank.

Battery Controller. The battery controller switches the electrical bus from the solar array to thebattery at the start of the eclipse, then back again at the conclusion. This action can beautomatic or done by ground control. The battery controller also maintains the batteries using

a light “trickle” charge (coming from a special “charge” solar array) and also periodicallycommands a rapid discharge into resistors for cell reconditioning. Such procedures prolongcell life to 10 years or more.

Battery Characteristics. The size of the batteries is proportional to the power requirements fora given space craft. The batteries are designed to be very light and efficient. Nickel-Cadmiumbatteries are being replaced by the more efficient Nickel-Hydrogen batteries.


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Power Management Issues:

Geostationary orbits present some interesting challenges for power management. Tounderstand these challenges, we must first understand a little about the attitude (orientation inspace) of geostationary satellites and the position of the geostationary orbit relative to the sun.

All modern geostationary spacecraft use one of two forms of stabilization to maintain theirattitude: dual-spin or three-axis stabilization. With dual-spin stabilization, the satellite takes theshape of a cylinder which rotates about its long axis. This type of satellite has two sections: aspinning section upon which the solar arrays are mounted and a despun section where thecommunications antennas are mounted. The spinning section provides basic stabilization andcan rotate as fast as 100 RPM (in the case of the early GOES satellites). The despun sectionrotates, too, albeit at a much slower rate of one rotation per orbit (day)—keeping the antennaspointed at the earth and preventing the satellite from going into a flat spin (which is the naturaltendency).

With three-axis stabilization, the spacecraft attitude is maintained through the use ofmomentum wheels or control moment gyros. The body of the spacecraft does rotate once perorbit (day) to keep the antennas pointed at the earth. The solar arrays are mounted on paddleswhich also rotate once per day to keep them pointed toward the sun.

In both cases, it should be noted that the rotation axis of the satellite is perpendicular to thesatellite's orbital plane—which for geostationary orbits is the equatorial plane. We will see whythis is important shortly.

As with all satellites, the solar arrays on geostationary satellites are subject to a numberfactors which can result in significant fluctuations in the amount of power available to onboardsystems. To begin with, the position of the satellite relative to the sun varies throughout the

year. As the earth goes around its orbit, its distance from the sun changes from a minimum of0.983 astronomical units (AUs—the mean distance from the earth to the sun is approximately 1AU or 149,597,870 km) to a maximum of 1.067 AU—a difference of 12,518,000 km. If weconsider the energy received from the sun at 1 AU to be 100%, then the energy receivedvaries from 97% to 103%, as shown in on the following page.


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Power Management Issues (cont.)

Not only isn't the earth's orbit truly circular, but the plane of the earth's equator does not lie inthe plane of the earth's orbit (the ecliptic). Earth's seasons are a direct result of thiscircumstance. From our vantage on earth, it appears that the sun slowly moves from 23°belowthe equatorial plane (at the winter solstice) to 23°above the equatorial plane (at the summersolstice) and back again over the course of a year. As seen in in the illustration below, ourgeostationary satellite sees the same thing.


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The apparent motion of the sun above and below the equatorial plane has two effects. First, itchanges the angle of incidence of solar energy received on the solar arrays since they must

rotate about an axis perpendicular to the equatorial plane. As a result, the amount of solarenergy absorbed by the solar arrays drops off as a factor of cos(), where is the sun'sdeclination (angle relative to the equatorial plane). If we consider the amount of energyreceived when the sun's rays are perpendicular to the solar arrays to be 100%, then theenergy received drops to less than 92% at the solstices, as shown in the illustration below:


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We can also see that because of this sun-earth geometry, the geostationary orbit is usuallyoutside the cone of the earth's shadow. That is, until around the times of the vernal and

autumnal equinoxes (the beginning of spring and fall). At these times, geostationary satellitesenter their eclipse season, when they can spend as much as 70 minutes of every day inshadow. These seasons run from the end of February through the middle of March and thebeginning of September through the middle of October. The percentage of sunlight receivedfor geostationary satellites is shown in in the illustration below. To prepare for eclipse seasons,the satellite operators must ensure that the spacecraft batteries are properly conditioned topick up the load during each day's eclipse.

If we combine the effects of variations in solar distance, solar angle, and eclipses over thecourse of a year, we get the result in the figure as show below. As can be seen in the figure,total solar energy available varies 12%—from a low of 89% to a high of 101%.


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If we also factor in the effects of degradation on the solar cells and their optical coverings dueto the space environment and look at a nominal seven-year satellite lifetime, we get the graph

in the figure below. Typical results show the optical covering degrades about 7% the first yearbefore stabilizing while the solar cells degrade about 3% their first year and 2% eachsubsequent year. As can be seen from the graph, the power levels drop from a high of 99%overall efficiency to a low of 72%. When designing the spacecraft power subsystem, thatmeans if 7.5 kW of power are required for normal operations, the power subsystem must bedesigned to provide almost 10kW initially so that available power doesn't drop below thethreshold before the end of the planned satellite lifetime.

Solar Interference:

In addition to planning for variations in spacecraft power, satellite operators and users alsoneed to plan for communications outages (or degradation) around the eclipse seasons. As thesun sweeps across the sky each day and gradually moves north or south with the seasons,there will come a time twice each year when the sun is directly behind a geostationary satelliteas seen from a ground-based antenna. When this happens, the flood of solar radio energy intothe antenna's main lobe can severely disrupt communications. Fortunately, such disruptionsonly last a couple of minutes. You may have actually seen one of these outages whilewatching your favorite cable channel (most of which are transmitted via geostationarysatellites). For observers in the Northern Hemisphere, this happens prior to vernal equinox andafter the autumnal equinox.


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Pointing and Stabilization

N

S

YAW

ROLL

PITCH

To ensure effective communications at all times, the designated side of the satellite that hasthe antennas attached to it is always pointed toward the Earth.

This orientation is done by rotating the body of the satellite in increments, so that the fullrotation is completed every 24 hours.

Using the Three-Axis stabilization, the spacecraft’s body maintains a fixed altitude relative tothe satellite’s orbital track and the Earth’s surface.

This system is called the Inertial Platform and is the same type of technology that is used forInertial Navigation for ships and airplanes.

Three Axis. The three axis that define the stabilization platform are: Pitch, Roll, and Yaw.

Factors that make pointing difficult are: The Earth’s rotation, The Earth’s North/South wobble,radiation pressure from the Sun, and gravity attraction from the Sun and Moon.

Components that aid pointing are: Thrusters, Earth Sensors, and Time of Day Clock.


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Inverse Proportion Law: This law relates to the focused bandwidth of an antenna.

“As the size of the antenna increases and the frequency used stays the same, the beam-widthangle becomes smaller and as the frequency increases with the same size antenna, thebandwidth angle becomes smaller”.

Antenna Sizes. The Inverse Proportion Law is reflected in the different antenna sizerequirements for C-Band and Ku-Band antennas. For example the size requirements, based onthe latest network topology, are:

C-Band: 6 feet (1.80 m) to 8 feet (2.40 m)

Ku-Band: 2 feet (0.55 m) to 4 feet (1.20 m)

Antenna Gain. This is the most important measurement of an antenna’s performance.

Assuming both the antenna and the isotropic source are being driven with the same amount ofRF power; the gain is defined by taking the ratio of intensity in a specific direction to that of anisotropic source. In the figure below, the ratio is 10:1.

Main Beam

Unity Gain

(Isotropic)

Peak Gain

Antenna Characteristics

Beam width angle becomes wider

as antenna becomes smaller or

the signal is lower in frequency.

Beam width angle becomes narrowas antenna becomes larger or

the signal is higher in frequency.


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Satellite Components:

The satellite is composed of three separate units, namely the fuel system, the satellite andtelemetry controls, and the transponder. The transponder includes the receiving antenna topick-up signals from the ground station, a broad band receiver, an input multiplexer, and afrequency converter which is used to reroute the received signals through a high poweredamplifier for downlink. The primary role of a satellite is to reflect electronic signals. In the caseof a telecom satellite, the primary task is to receive signals from a ground station and sendthem down to another ground station located a considerable distance away from the first. Thisrelay action can be two-way, as in the case of a long distance phone call. Another use of thesatellite is when, as is the case with television broadcasts, the ground station's uplink is thendownlinked over a wide region, so that it may be received by many different customerspossessing compatible equipment. Still another use for satellites is observation, wherein thesatellite is equipped with cameras or various sensors, and it merely downlinks any information

it picks up from its vantage point.

Transponders

Antennas

Power System & SolarPanels

Guidance System

Propulsion Jets

RF Equipment

Switching and

RedundancyComponents

Satellite Components


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The basic function of the satellite transponder is to isolate individual carriers or groups of

carriers and to boost their power level before they are retransmitted to the ground. The carrierfrequencies are also altered as the carriers pass through the satellite.

Satellite transponders that process the carrier in this way are typically referred to as atransparent transponders. Only the basic radio frequency characteristics of the carrier(amplitude and frequency) are altered by the satellite. The detailed carrier format, such as themodulation characteristics and the spectral shape, remains unchanged.

In nearly all cases, the Low Noise Amplifier precedes the transponder and is common to alltraffic being received at the satellite. Typically such a device will have over 500 MHz bandwidth.

The frequency converter also precedes the transponder and a block converts the entire 500MHz of BW to the new downlink band.. All transponder processing is of amplified signals and atdownlink frequencies.

The IMUX consists of bandpass filters, each 36 MHz (or whatever the transponder BW is)allowing traffic destined for a given transponder, only to be processed by that particulartransponder.

The TWTA amplifies the signals. The Output Isolator protects the TWTA from reflected power.Output switching allows redundant chains to be used as required and the OMUX re-combinesall transponder outputs prior to being transmitted by the antenna.

What is a Transponder ?

Satellite equipment that receives signals on the uplink,translates them to the downlink frequency, and amplifies themfor retransmission to earth

Usually 12-16 Transponders per satellite (Ku-Band) – 36-72MHz each

Transponder Components:

Low Noise pre-amplifier

Frequency Converter

Mixer

Internal multiplexer (IMUX)

High Power Traveling wave Tube Amplifier (TWTA)Output isolator

Output switching

Output multiplexer (OMUX)


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Typical Satellites have a bandwidth of 500 MHz split into 12 transponders of approximately 36MHz each. Two transponders can use different polarization, allowing re-use of the samefrequency without interference.

Modern Satellites use TDM - Time Division Multiplexing and can contain several antennas,each allowing a focused footprint of coverage on the Earth called ‘Spot Beams’.

The Low Noise Amplifier - LNA detects amplifies the signal (along with the noise) and acts as atuned filter, allowing only the signals on the frequency range of the transponder to pass.

The Mixer and Local Oscillator convert the incoming signal to the downlink frequency.

The bandpass filter allows only the desired frequency to pass to the HPA.

Some satellites contain an IMUX (Internal Multiplexer) which allows switching betweendifferent transponders on the same satellite.

Finally, the HPA - High Power Amplifier, amplifies the signal to be fed into the transmittingantenna for rebroadcast.

Band Pass

Filter

RX Antenna

14.0-14.5 GHz (F1)

TX Antenna

11.7- 12.2 GHz

Low Noise

Amplifier

Local Oscillator (F2)

Mixer

High Power

Amplifier

IMUX

F1-F2 F1 +F2

F1-2F2 F1+2F2

F1-3F2 F1+3F2

F1-4F2 F1+4F2

. .

. .

. .

F1-F2 F1 +F2

F1-2F2 F1+2F2

F1-3F2 F1+3F2

F1-4F2 F1+4F2

. .

. .

. .

Output after mixer

Transponder Block Diagram

and

Unwanted Harmonics


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Tracking, Telemetry & Command Station

CommandSubsystem

Ranging

Subsystem

Telemetry

Subsystem

I.F. Switching

and Control

Subsystem

Full Tracking

TTAC Antenna

Limited Motion Communication Antennas

Up-Link

DownLink

Up-Link

DownLink

Satellite

Control

Center

(SCC)*

*SCC. The brain of

the operation. Suppliescomputing power and

human intelligence.

Can be co-located or at

a distance.

The TT&C has essentially the same capability as the generic earth station, incorporating the RFterminal, baseband equipment, and the terrestrial interface. The antennas employed areusually 10 to 13 meters in diameter (whether C or Ku Band) to provide the maximum possiblelink margin since abnormal conditions need to be accommodated. Major components of theTT&C are:

Limited Motion Antenna. For communicating and tracking each operational satellite. (Tw

02 skyedge basic satellite

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