Satellite Communication Notes

Department of ECE Department of ECE

Lecture Notes Lecture Notes EC1015 -

EC1015 - SATSATELLITE COMMUNICATIONELLITE COMMUNICATION

Unit I

Unit I

Overvie of Sate!!ite S"stems# Or$its an%

Overvie of Sate!!ite S"stems# Or$its an% Launc&in' Met&o%s

Launc&in' Met&o%s

Communication Communication

Sate!!ite(-A communications satellite (Comsat) is an artificial satellite stationed in space for the purposes of  A communications satellite (Comsat) is an artificial satellite stationed in space for the purposes of  telecommunications. Modern communications satellites use geostationary orbits, Molniya orbits or  telecommunications. Modern communications satellites use geostationary orbits, Molniya orbits or  low polar Earth orbits. They are also used for mobile applications such as communications to ships low polar Earth orbits. They are also used for mobile applications such as communications to ships and

and plplananeses, , fofor r whwhicich h apapplplicicatatioion n of of otother her tetechchnonolologigieses, , susuch ch as as cacablble, e, arare e imimprpracactitical cal or or  impossible.

impossible.

U.. military M!"TA# communications satellite U.. military M!"TA# communications satellite

Ear!"

Ear!"

Missions(-The first satellite e%uipped with on&board

The first satellite e%uipped with on&board radioradio&&transmitterstransmitters was the o'iet putni $, launched in was the o'iet putni $, launched in $*+. The first American satellite to relay communications

$*+. The first American satellite to relay communications was proect score inwas proect score in $*-$*-,, which used a which used a tape recorder to

tape recorder to store and forwardstore and forward 'oice messages. !t was used to send a Christmas greeting to the 'oice messages. !t was used to send a Christmas greeting to the world from

world from resident Eisenhower resident Eisenhower ..

 /AA

 /AA launched an launched an Echo satellite inEcho satellite in $01$012 the 2 the $11&fo$11&foot alumini3ot alumini3eded ET filmET film balloon ser'ed as a balloon ser'ed as a  passi'e

 passi'e reflector reflector for for radio radio communications. communications. Courier Courier $4, $4, (built (built byby hilcohilco) also launched in $01,) also launched in $01, was the world5s first acti'e repeater satellite.

was the world5s first acti'e repeater satellite.

Te

Telstar was the first acti'e, direct relay lstar was the first acti'e, direct relay communications satellite. !t was placed in communications satellite. !t was placed in an ellipticalan elliptical orbitorbit

(completed once e'ery 6 hours and 7+ minutes), rotating at a 8*9 angle abo'e the

(completed once e'ery 6 hours and 7+ minutes), rotating at a 8*9 angle abo'e the e%uator e%uator ..

The first truly geostationary satellite launched in orbit was the yncom 7, launched on

The first truly geostationary satellite launched in orbit was the yncom 7, launched on August $August $,, $08. !t was placed in orbit at $-19 east

$08. !t was placed in orbit at $-19 east longitudelongitude, o'er the, o'er the !nternational :ate "ine!nternational :ate "ine. !t was used. !t was used that same year to relay tele'ision co'erage on the

that same year to relay tele'ision co'erage on the $08 ummer ;lympics$08 ummer ;lympics in in ToyoToyo to the to the UnitedUnited

tates

tates, the first tele'ision transmission sent o'er the acific ;cean., the first tele'ision transmission sent o'er the acific ;cean.

hortly after

hortly after yncom 7yncom 7,, !ntelsat !!ntelsat !, aa Early 4ird, was launched on, aa Early 4ird, was launched on April 0April 0,, $0*$0* and placed inand placed in orbit at 6-9 west longitude. !t was the first geostationary satellite for telecommunications o'er the orbit at 6-9 west longitude. !t was the first geostationary satellite for telecommunications o'er the Atlantic ;cean

Atlantic ;cean..

)eostationar"

)eostationar"

Sate!!ites(-A satellite in a

A satellite in a geostationary orbitgeostationary orbit appears to be in a fi<ed position to an earth based obser'er. A appears to be in a fi<ed position to an earth based obser'er. A geostationary satellite re'ol'es around the earth at a constant speed once per day o'er the e%uator. geostationary satellite re'ol'es around the earth at a constant speed once per day o'er the e%uator.

The

The geosgeostattationionary ary atatellellite ite is is useuseful ful for for comcommunmunicaicatiotion n applapplicaicatiotions ns thathat t useuses s groground und basbaseded antennas, which must be directed toward the satellite, can operate effecti'ely without the need for  antennas, which must be directed toward the satellite, can operate effecti'ely without the need for  e<pensi'e e%uipment

e<pensi'e e%uipment to trac the satellite5s motion.to trac the satellite5s motion.

Lo Eart&

Lo Eart& Or$itin' Sate!!ites(-

Or$itin'

Sate!!ites(-A "ow Earth ;rbit ("E;) typically is a circular orbit about 811 ilometers abo'e the earth5s A "ow Earth ;rbit ("E;) typically is a circular orbit about 811 ilometers abo'e the earth5s surface and, correspondingly, a period (time to re'ol'e around the earth) of about 1 minutes. surface and, correspondingly, a period (time to re'ol'e around the earth) of about 1 minutes. 4ecause of their low altitude, these satellites are only 'isible from within a radius of roughly $111 4ecause of their low altitude, these satellites are only 'isible from within a radius of roughly $111 6 6

Ear!"

Ear!"

Missions(-The first satellite e%uipped with on&board

The first satellite e%uipped with on&board radioradio&&transmitterstransmitters was the o'iet putni $, launched in was the o'iet putni $, launched in $*+. The first American satellite to relay communications

$*+. The first American satellite to relay communications was proect score inwas proect score in $*-$*-,, which used a which used a tape recorder to

tape recorder to store and forwardstore and forward 'oice messages. !t was used to send a Christmas greeting to the 'oice messages. !t was used to send a Christmas greeting to the world from

world from resident Eisenhower resident Eisenhower ..

 /AA

 /AA launched an launched an Echo satellite inEcho satellite in $01$012 the 2 the $11&fo$11&foot alumini3ot alumini3eded ET filmET film balloon ser'ed as a balloon ser'ed as a  passi'e

 passi'e reflector reflector for for radio radio communications. communications. Courier Courier $4, $4, (built (built byby hilcohilco) also launched in $01,) also launched in $01, was the world5s first acti'e repeater satellite.

was the world5s first acti'e repeater satellite.

Te

Telstar was the first acti'e, direct relay lstar was the first acti'e, direct relay communications satellite. !t was placed in communications satellite. !t was placed in an ellipticalan elliptical orbitorbit

(completed once e'ery 6 hours and 7+ minutes), rotating at a 8*9 angle abo'e the

(completed once e'ery 6 hours and 7+ minutes), rotating at a 8*9 angle abo'e the e%uator e%uator ..

The first truly geostationary satellite launched in orbit was the yncom 7, launched on

The first truly geostationary satellite launched in orbit was the yncom 7, launched on August $August $,, $08. !t was placed in orbit at $-19 east

$08. !t was placed in orbit at $-19 east longitudelongitude, o'er the, o'er the !nternational :ate "ine!nternational :ate "ine. !t was used. !t was used that same year to relay tele'ision co'erage on the

that same year to relay tele'ision co'erage on the $08 ummer ;lympics$08 ummer ;lympics in in ToyoToyo to the to the UnitedUnited

tates

tates, the first tele'ision transmission sent o'er the acific ;cean., the first tele'ision transmission sent o'er the acific ;cean.

hortly after

hortly after yncom 7yncom 7,, !ntelsat !!ntelsat !, aa Early 4ird, was launched on, aa Early 4ird, was launched on April 0April 0,, $0*$0* and placed inand placed in orbit at 6-9 west longitude. !t was the first geostationary satellite for telecommunications o'er the orbit at 6-9 west longitude. !t was the first geostationary satellite for telecommunications o'er the Atlantic ;cean

Atlantic ;cean..

)eostationar"

)eostationar"

Sate!!ites(-A satellite in a

A satellite in a geostationary orbitgeostationary orbit appears to be in a fi<ed position to an earth based obser'er. A appears to be in a fi<ed position to an earth based obser'er. A geostationary satellite re'ol'es around the earth at a constant speed once per day o'er the e%uator. geostationary satellite re'ol'es around the earth at a constant speed once per day o'er the e%uator.

The

The geosgeostattationionary ary atatellellite ite is is useuseful ful for for comcommunmunicaicatiotion n applapplicaicatiotions ns thathat t useuses s groground und basbaseded antennas, which must be directed toward the satellite, can operate effecti'ely without the need for  antennas, which must be directed toward the satellite, can operate effecti'ely without the need for  e<pensi'e e%uipment

e<pensi'e e%uipment to trac the satellite5s motion.to trac the satellite5s motion.

Lo Eart&

Lo Eart& Or$itin' Sate!!ites(-

Or$itin'

Sate!!ites(-A "ow Earth ;rbit ("E;) typically is a circular orbit about 811 ilometers abo'e the earth5s A "ow Earth ;rbit ("E;) typically is a circular orbit about 811 ilometers abo'e the earth5s surface and, correspondingly, a period (time to re'ol'e around the earth) of about 1 minutes. surface and, correspondingly, a period (time to re'ol'e around the earth) of about 1 minutes. 4ecause of their low altitude, these satellites are only 'isible from within a radius of roughly $111 4ecause of their low altitude, these satellites are only 'isible from within a radius of roughly $111

il

ilomeometerters s frofrom m the the subsub&sa&sateltellitlite e poipoint. nt. !n !n addiadditiotion, n, satsatellelliteites s in in low low earearth th orborbit it chachange nge thetheir ir   position relati'e

 position relati'e to to the the ground ground position %uicly. position %uicly. o o e'en e'en for for local local applications, applications, a large a large number number of of  satellites are needed if

satellites are needed if the mission re%uires uninterrupted connecti'ity.the mission re%uires uninterrupted connecti'ity.

"ow earth orbiting satellites are less e<pensi'e to position in space than geostationary satellites "ow earth orbiting satellites are less e<pensi'e to position in space than geostationary satellites and, because of their closer

and, because of their closer pro<imity to the ground, re%uire lower signal strength.pro<imity to the ground, re%uire lower signal strength.

A group of

A group of satsatellellitites es worworining g in concerin concert t thuthus s is nown as is nown as aa satellite constellationsatellite constellation. Two such. Two such constellations which were intended for pro'ision for hand held telephony, primarily to remote constellations which were intended for pro'ision for hand held telephony, primarily to remote areas, were the

areas, were the !ridium and =lobalstar. The !ridium system has 00 satellites.!ridium and =lobalstar. The !ridium system has 00 satellites.

!t is also possible to offer discontinuous co'erage using a low Earth orbit satellite capable of  !t is also possible to offer discontinuous co'erage using a low Earth orbit satellite capable of  storing data recei'ed while passing o'er one part of Earth

storing data recei'ed while passing o'er one part of Earth and transmitting it later while passingand transmitting it later while passing o'e

o'er r ananototheher r papartrt. . ThThis is wiwill be ll be ththe e cacase se wiwith th ththe e CACACCA:A:E E sysyststem em ofof CanadaCanada5s5s cassiopecassiope communications satellite.

communications satellite.

Lo *o!ar Eart& Or$it

Lo *o!ar Eart& Or$it

 Sate!!ites(-

As menmentitionedoned, , geogeostastatiotionary nary satsatellellitites es are are conconstrstrainained ed to to operoperate ate aboabo'e 'e the the e%uae%uatortor. . As As aa conse%uence, they are not always suitable for pro'iding ser'ices at high latitudes> for at high conse%uence, they are not always suitable for pro'iding ser'ices at high latitudes> for at high latitudes a geostationary satellite may appear low on (or e'en below) the hori3on, affecting latitudes a geostationary satellite may appear low on (or e'en below) the hori3on, affecting connecti'ity and causing multipathing (interference caused

connecti'ity and causing multipathing (interference caused by signals reflecting off the ground intoby signals reflecting off the ground into the ground antenna). The first satellite of

the ground antenna). The first satellite of MolniyaMolniya series was launched on April 67, series was launched on April 67, $0*$0* and was and was us

used ed fofor r e<e<peperirimementntalal transmissiontransmission oof Tf T?? signalsignal. Th. The e MoMolnlniyiya a ororbibit t is is hihighghly ly ininclclinineded,, guar

guarantanteeieeing ng googood d eleele'at'ation ion o'eo'er r selselectected ed pospositiitions ons durduring ing the the nornorthethern rn porportiotion n of of the the orborbit.it. (Ele'ation is the e<tent of the satellite5s position abo'e the hori3on. Thus a satellite at the hori3on (Ele'ation is the e<tent of the satellite5s position abo'e the hori3on. Thus a satellite at the hori3on has 3ero ele'ation and a satellite directly o'erhead has ele'ation of 1 degrees).

has 3ero ele'ation and a satellite directly o'erhead has ele'ation of 1 degrees).

@urthermore, the Molniya orbit is so designed that the satellite spends the great maority of its time @urthermore, the Molniya orbit is so designed that the satellite spends the great maority of its time o'er the far northern latitudes, during which its ground footprint mo'es only slightly. !ts period is o'er the far northern latitudes, during which its ground footprint mo'es only slightly. !ts period is one half day, so that the satellite is a'ailable for operation o'er the targeted region for eight hours one half day, so that the satellite is a'ailable for operation o'er the targeted region for eight hours e'ery second re'olution. !n this way a constellation of three Molniya satellites (plus in&orbit e'ery second re'olution. !n this way a constellation of three Molniya satellites (plus in&orbit spares) can pro'ide uninterrupted co'erage.

spares) can pro'ide uninterrupted co'erage.

Mo

Molnlniyiya a sasatetellllitites es arare e tytypipicalcally ly usused ed fofor r tetelelephphony ony and and T? T? seser'r'icices es o'eo'err #ussia#ussia. . AnAnothother er  application is to use them for mobile radio systems (e'en at lower latitudes) since cars tra'elling application is to use them for mobile radio systems (e'en at lower latitudes) since cars tra'elling 7 7

through urban areas need access to satellites at high ele'ation in order to secure good connecti'ity, through urban areas need access to satellites at high ele'ation in order to secure good connecti'ity, e.g. in the presence of tall buildings.

e.g. in the presence of tall buildings.

App!ications(- Te!ep&on"(-The

The firfirst st and and hishistortoricaically lly the the mosmost t imimportportant ant appappliclicatiation on for for comcommunmunicaicatiotion n satsatellelliteites s is is inin international

international telephonytelephony. @i<ed&point telephones relay calls to an earth station, where they are then. @i<ed&point telephones relay calls to an earth station, where they are then transmitted to a geostationary satellite. An analogous path is then followed on the downlin. !n transmitted to a geostationary satellite. An analogous path is then followed on the downlin. !n cont

contrasrast, t, mobmobilile e teltelephoephones nes (t(to o and and frofrom m shiships ps and and airairplaplanesnes) ) musmust t be be dirdirectectly ly connconnectected ed toto e%uipment to uplin the signal to the satellite, as well as being able to ensure satellite pointing in e%uipment to uplin the signal to the satellite, as well as being able to ensure satellite pointing in the presence of disturbances, such as wa'es onboard a ship.

the presence of disturbances, such as wa'es onboard a ship. Sate!!ite Te!evision an%

Sate!!ite Te!evision an%

+a%io(-Tele'ision became the main maret, its demand for simultaneous deli'ery of relati'ely few signals Tele'ision became the main maret, its demand for simultaneous deli'ery of relati'ely few signals of l

of laarrggee  bandwidth bandwidth to to mamany ny rerececei'i'erers s beibeing ng a a momore re prprececisise e mamatctch h fofor r ththe e capcapababililititieies s of of  geosynchronous comsats. Two satellite types are used for /orth American tele'ision and

geosynchronous comsats. Two satellite types are used for /orth American tele'ision and radio>radio>

•

• _{:irect 4roadcast atellite:irect 4roadcast atellite (:4), and(:4), and}

•

• @i<ed er'ice atellite@i<ed er'ice atellite (@). (@).

A

A direct broadcast satellitedirect broadcast satellite  is a communications satellite that transmits to small :4 satellite  is a communications satellite that transmits to small :4 satellite dishes (usually $- to 68 inches in diameter). :irect broadcast satellites generally operate in the dishes (usually $- to 68 inches in diameter). :irect broadcast satellites generally operate in the upper portion of the microwa'e

upper portion of the microwa'e   uu  band  band. :4 technology is used for :TB&oriented (. :4 technology is used for :TB&oriented (:irect&To&:irect&To&

Bome

Bome) satellite T? ser'ices, such as) satellite T? ser'ices, such as :irecT?:irecT?,, :!B /etwor :!B /etwor ..

@i<ed er'ice atellites

@i<ed er'ice atellites use the use the C bandC band, and the lower portions of the  , and the lower portions of the  uu bands. They are normally bands. They are normally

used for broadcast feeds to and from tele'ision networs and local affiliate stations (such as used for broadcast feeds to and from tele'ision networs and local affiliate stations (such as  program

 program feeds feeds for for networ networ and and syndicated syndicated programming,programming, li'e shotsli'e shots, and, and bachauls bachauls), as well as), as well as  being

 being used used forfor distadistance nce learnlearninging by by scschohoolols s anand d ununi'i'erersisititieses,,  business  business tele'isiontele'ision  (4T?),  (4T?), ?ideoconferencing

?ideoconferencing,, and general commercial telecommunications. @ satellites are also used to and general commercial telecommunications. @ satellites are also used to distribute national cable channels to

distribute national cable channels to cable T?cable T? headends. headends.

@ satellites differ from :4 satellites> @ satellites differ from :4 satellites>

•

•

• _{@ re%uires a much larger dish for reception (7 to - feet in diameter for  @ re%uires a much larger dish for reception (7 to - feet in diameter for  uu  band, and  band, and}

$6 feet on up for C band). $6 feet on up for C band).

•

• _{@ use@ use linear polari3ationlinear polari3ation for each of the transponders #@ input and output where as :4 for each of the transponders #@ input and output where as :4}

satellites use

satellites use circular polari3ationcircular polari3ation..

@ree&to&air 

@ree&to&air satellite T? channels are also usually distributed on @ satellites in the  satellite T? channels are also usually distributed on @ satellites in the  uu band. band. Mo$i!e Sate!!ite

Mo$i!e Sate!!ite Tec&no!o'ies(-!ni

!nitiatially lly a'aa'ailailable ble for for brobroadcadcast ast to to stastatiotionarnary y T? T? recrecei'ei'ersers, , by by 6118 6118 poppopulaular r mobmobile ile dirdirectect  broadcast applications

 broadcast applications made their made their appearance with appearance with that arri'al of that arri'al of two satellite radio two satellite radio systems in thesystems in the United tates> irius and DM atellite #adio Boldings. ome manufacturers ha'e also introduced United tates> irius and DM atellite #adio Boldings. ome manufacturers ha'e also introduced special antennas for mobile reception of :4 tele'ision. Using

special antennas for mobile reception of :4 tele'ision. Using == technology as a reference, technology as a reference, these antennas automatically re&aim to the satellite no matter where or how the 'ehicle (that the these antennas automatically re&aim to the satellite no matter where or how the 'ehicle (that the antenna is mounted on) is situated. uch mobile :4 antennas are also used by

antenna is mounted on) is situated. uch mobile :4 antennas are also used by et4lue Airwayset4lue Airways

for :irecT? which passengers can 'iew on&board on

for :irecT? which passengers can 'iew on&board on "C: screens mounted in the seats."C: screens mounted in the seats. Amateur

Amateur +a%io(-Amateur radio

Amateur radio operators ha'e access to the ;CA# satellites that ha'e been designed specifically operators ha'e access to the ;CA# satellites that ha'e been designed specifically to

to carcarry ry amaamateuteur r radradio io tratraffffic. ic. MosMost t sucsuch h satsatellelliteites s opeoperatrate e as as spaspacebocebornerne repeatersrepeaters, and are, and are gen

genereralally ly accaccesessesed d by by amamatateueurs rs e%e%uiuipppped ed wiwithth UB@UB@ or ?B@or ?B@ radradio io e%ue%uipmipment ent and and highighlyhly dir

directectionionalal antennasantennas such such as as FFaagis or gis or disdish h antantennennas. as. :ue :ue to to the limithe limitattationions s of of groground&und&basbaseded amateur e%uipment, most amateur satellites are launched into fairly low Earth orbits, and are amateur e%uipment, most amateur satellites are launched into fairly low Earth orbits, and are designed to deal with only a limited number of brief contacts at any gi'en time. ome satellites designed to deal with only a limited number of brief contacts at any gi'en time. ome satellites also pro'ide data&forwarding ser'ices using the

also pro'ide data&forwarding ser'ices using the AD.6*AD.6* or similar protocols. or similar protocols. Sate!!ite

Sate!!ite

,roa%$an%(-!n recent years, satellite communication technology has been used as a means to connect to the !n recent years, satellite communication technology has been used as a means to connect to the !nternet

!nternet 'ia broadband data connections. This can be 'ery useful for users who are located in 'ery'ia broadband data connections. This can be 'ery useful for users who are located in 'ery remote areas, and cannot access a wireline

remote areas, and cannot access a wireline broadband broadbandoror dialupdialupconnection.connection.

* *

re.uenc" ,an%s for Sate!!ite

Communication(-/&at is C ,an%

C 4and is the original fre%uency allocation for communications satellites. C&4and uses 7.+&8.6=B3 for downlin  and *.6*&0.86*=h3 for uplin .

The lower fre%uencies used by C 4and perform better under ad'erse weather conditions than the u band or a band fre%uencies.

C ,an% ariants

light 'ariations of C 4and fre%uencies are appro'ed for use in 'arious parts of the world.

,an% T2 re.uenc" +2 re.uenc"

E<tended C 4and *.-*1 & 0.86* =B3 7.06* & 8.611 =B3 uper E<tended C&4and *.-*1 & 0.+6* =B3 7.811 & 8.611 =B3 !/AT C&4and 0.+6* & +.16* =B3 8.*11 & 8.-11 =B3 alapa C&4and 0.86* & 0.+6* =B3 7.811 & 7.+11 =B3 #ussian C&4and *.+* & 0.8+* =B3 7.0*1 & 8.$*1 =B3 "M! C&4and *.+6*1 & 0.16* =B3 7.+11 & 8.111 =B3

C ,an% Dis&es

C 4and re%uires the use of a large dish, usually 0 across. C 4and dishes 'ary between 7 and  across, depending upon signal strength.

4ecause C 4and dishes are so much larger than u and a 4and dishes, a C 4and dish is sometimes referred to in friendly est as a 4U: (4ig Ugly :ish).

/&at is 3u $an%

The u band (urt3&under band) is primarily used for satellite communications, particularly for editing and broadcasting satellite tele'ision. This band is split into multiple segments broen down into geographical regions, as determined by the !TU (!nternational Telecommunication Union). The u band is a portion of the electromagnetic spectrum in the microwa'e range of fre%uencies ranging from $$.+ to $6.+=B3. (downlin fre%uencies) and $8 to $8.*=B3 (uplin fre%uencies). The most common u band digital reception format is :?4 (main profile 'ideo format) .'s the studio profile digital 'ideo format or the full&blown :igicipher !! 8:T? format.

The first commercial tele'ision networ to e<tensi'ely utili3e the u 4and for most of its affiliate feeds was /4C, bac in $-7.

The !TU #egion 6 segments co'ering the maority of the Americas are between $$.+ and $6.6 =B3, with o'er 6$ @ /orth American u&band satellites currently orbiting.

Each re%uires a 1.-&m to $.*&m antenna and carries twel'e to twenty four transponders, of which consume 61 to $61 watts (per transponder), for clear reception.

The $6.6 to $6.+ =B3 segment of the u 4and spectrum is allocated to the broadcasting satellite ser'ice (4). These direct broadcast satellites typically carry $0 to 76 transponders.

Each pro'ides 6+ MB3 in bandwidth, and consumes $11 to 681 watts each, accommodating recei'er antennas down to 8*1 mm ($- inches ).

The !TU #egion $ segments of the u spectrum represent Africa and Europe ($$.8* to $$.+ =B3  band range and $6.* to $6.+* =B3 band range) is reser'ed for the fi<ed satellite ser'ice (@),

with the uplin fre%uency range between $8.1 and $8.* =B3).

3u ,an% Difficu!ties

Ghen fre%uencies higher than $1 =B3 are transmitted and recei'ed used in a hea'y rain fall area, a noticeable degradation occurs, due to the problems caused by and proportional to the amount of rain fall (commonly nown as nown as Hrain fadeH).

This problem can be combatted, howe'er, by deploying an appropriate lin budget strategy when designing the satellite networ, and allocating a higher power consumption to o'ercome rain fade loss. !n terms of end&'iewer T? reception,

it taes hea'y rainfalls in e<cess of $11 mm per hour to ha'e a noticeable effect.

The higher fre%uency spectrum of the u band is particularly susceptible to signal degradation& considerably more so than C band satellite fre%uency spectrum, though the u band is less 'ulnerable to rain fade than the a band fre%uency spectrum.

A similar phenomena, called Hsnow fadeH (when snow accumulation significantly alters the focal  point of your dish) can also occur during Ginter eason.

Also, the u band satellites typically re%uire considerably more power to transmit than the C band satellites. Bowe'er, both u and a band satellite dishes to be smaller ('arying in si3e from 6 to * in diameter.)

3u ,an% Sate!!ite Service Don!in4 Usa'e re.uenc" +an'e

The u band downlin  uses fre%uencies between $$.+ and $6.+=B3.

The u band downlin fre%uencies are further subdi'ided according to their assigned use>

3u ,an% Usa'e Don!in4  

@i<ed atellite er'ice $$.+ & $6.6=B3 4roadcast atellite er'ice $6.6 & $6.+=B3

er'ices that can be found on the u&band include educational networs, business networs, sports  bachauls, tele& conferences, mobile news truc feeds, international programming, and 'arious

CC (ingle Channel er Carrier) transmissions of analog audio, as well as @M audio ser'ices. !f you already ha'e a operational C&band system in place, you can retrofit it to accept u band fre%uencies.

!n order to do so, you will need to obtain a u&band "/4 as well as a CIu band feed&horn, plus some coa< cable for your u&band "/4.

As for the coa< cable recommended& #=&0 is optimal for low loss in the *1&$8*1 fre%uency range& what u&band "/4 processes. Bowe'er, if #=&* is your only 'iable option, itll wor in a  pinch.

3u ,an% Dis& Antenna Compati$i!it"

!if you ha'e a solid dish, you should ha'e no problem con'erting from C band, to u band.

Bowe'er, with a mesh dish& if the HholesH in the mesh are greater than a %uarter inch, the chances of computability are not in your fa'or, due to the fact that your dish wont reflect u&band signals  properly.

Therefore, youll want to strongly consider upgrading to either a solid dish, or a mesh dish in which the hole si3e under $I8H, and ideally youll want a dish that is $ piece (or at least 'ery few  pieces)2 as 8 section dish is more optimal than an - section dish.

The fewer the sections, the more accurate your parabola shape is and thereby the more difficult it is for your dish to become warped (the smaller the number of seams& the better). And insofar as dish mounts go, the B6B (Bori3on&to&Bori3on) dish mount is more desirable than a polar mount.

This is due to the fact that the u&band demands that the dish antenna system is well&targeted and able to closely follow the orbital arc, of which the B6B mount does %uite admirably, as compared to a polar mount. Also, bear in mind that you will be adusting both the a3imuth and ele'ation, which can be a bit tricy occasionally.

Importance of Sate!!ite Antenna Dis& *ara$o!a

The parabolic shape of your dish is of critical importance, as warpage causes signal degradation 'ia mis&reflection, seriously down&grading your o'erall system performance. ome tape and string is all that is re%uired to do a %uic warpage chec and some tape.

Anchor a piece of string, stretched as tight as possible, HnorthH to HsouthH across your dish face, edge to edge. Foull want to do the same thing again, with another piece of string, only HeastH to HwestH across the dish face& at 1 degree angles. 4e sure that both strings are tight&

!f the strings come together anywhere but the direct center, then your dish has sustained warp damage and needs to be bent bac into proper parabola shape, for optimal performance. !f they connect in the center of your dish, liely that your dish is not warped.

o therefore, youll want to use either the tri&supports or %uad supports , as they will greatly assist in eeping your u&band feed&horn highly stable, e'en in high winds.

Ghen your button&hoo feed mo'ing in the wind, your u&band reception can can easily drop out. 4y putting guy&wires on the button&hoo feed, youll create the much&needed support, in the e'ent you are not able to obtain a tri support or %uad support.

/&at is 3a $an%

The a band uplin  uses fre%uencies between 6+.*=B3 and 7$=h3 and the downlin  uses fre%uencies between $-.7 and $-.-=h3 and between $.+ and 61.6=h3.

a band dishes can be much smaller than C band dishes. a band dishes 'ary from 6 to * in diameter.

a band satellites typically transmit with much more power than C band satellites.

The higher fre%uencies of a band are significantly more 'ulnerable to signal %uality problems caused by rainfall, nown as rainfade

/&at is L $an%

" band is a fe%uency range between 71MB3 and $.**=B3 which is used for satellite communications and for terrestrial communications between satellite e%uipment.

The high fre%uencies utili3ed by C band, u band, and a band would suffer from high signal loss when transported o'er a copper coa< cable such as an !ntra&@acility "in .

An "/4 is used to con'ert these higher fre%uency bands to " band, which can be transmitted o'er the !@" and processed by the !:U.

ome satellites transmit on " band, such as = satellites

/&at is S $an%

 band is a fre%uency range from appro<imately $.** to *.6=B3 which is used for :igital Audio #adio atellite (:A#) satellite radio systems such as irius atellite #adio and DM atellite #adio.

 band is also used by some weather and communications satellites.

In%ian Sate!!ites

Sl.No. Satellite Launch

Date Achievements

1. Aryabhata 19.04.1975

First Inian satellite. !rovie technolo"ical e#$erience in builin" an o$eratin" a satellite system. Launche by %ussian launch vehicle Intercosmos.

&. 'has(ara)I 07.0*.1979

First e#$erimental remote sensin" satellite. +arrie ,- an microave cameras. Launche by %ussian launch vehicle Intercosmos.

/. 'has(ara)II &0.11.191

Secon e#$erimental remote sensin" satellite similar to 'has(ara)1. !rovie e#$erience in builin" an o$eratin" a remote sensin" satellite system on an en)to)en basis. Launche by %ussian launch vehicle Intercosmos.

4.

Ariane !assen"er !ayloa #$eriment 2A!!L3

19.0*.191

First e#$erimental communication satellite. !rovie e#$erience in builin" an o$eratin" a three)a#is stabilise communication satellite. Launche by the uro$ean Ariane. 5. %ohini ,echnolo"y

!ayloa 2%,!3 10.0.1979

Intene or measurin" in)li"ht $erormance o irst e#$erimental li"ht o SL-)/ the irst Inian launch vehicle. +oul not be $lace in orbit.

*. %ohini 2%S)13 1.07.190 6se or measurin" in)li"ht $erormance o secon e#$erimental launch o SL-)/.

7. %ohini 2%S)D13 /1.05.191

6se or conuctin" some remote sensin" technolo"y stuies usin" a lanmar( sensor $ayloa. Launche by the irst evelo$mental launch o SL-)/

. %ohini 2%S)D&3 17.04.19/ Ientical to %S)D1. Launche by the secon evelo$mental launch o SL-)/. 9. Stretche %ohini Satellite Series 2S%SS) 13 &4.0/.197

+arrie $ayloa or launch vehicle $erormance monitorin" an or 8amma %ay astronomy. +oul not be $lace in orbit. 10. Stretche %ohini

Satellite Series 2S%SS)

1/.07.19 +arrie remote sensin" $ayloa o 8erman s$ace a"ency in aition to 8amma %ay astronomy $ayloa. +oul not be

&3 $laceinorbit. 11. Stretche %ohini Satellite Series 2S%SS) +3 &0.05.199&

Launche by thir evelo$mental li"ht o ASL-. +arrie 8amma %ay astronomy an aeronomy $ayloa.

1&.

Stretche %ohini

Satellite Series 2S%SS) +&3

04.05.1994

Launche by ourth evelo$mental li"ht o ASL-. Ientical to S%SS)+. Still in service.

Inian National Satellite System 2INSA,3

1/. INSA,)1A 10.04.19&

First o$erational multi)$ur$ose communication an meteorolo"y satellite $rocure rom 6SA. or(e only or si# months. Launche by 6S Delta launch vehicle.

14. INSA,)1' /0.0.19/ Ientical to INSA,)1A. Serve or more than esi"n lie o  seven years. Launche by 6S S$ace Shuttle.

15. INSA,)1+ &1.07.19 Same as INSA,)1A. Serve or only one an a hal years. Launche by uro$ean Ariane launch vehicle.

1*. INSA,)1D 1&.0*.1990 Ientical to INSA,)1A. Launche by 6S Delta launch vehicle. Still in service.

17. INSA,)&A 10.07.199&

First satellite in the secon)"eneration Inian)built INSA,)& series. :as enhance ca$ability than INSA,)1 series. Launche by uro$ean Ariane launch vehicle. Still in service. 1. INSA,)&' &/.07.199/ Secon satellite in INSA,)& series. Ientical to INSA,)&A.

Launche by uro$ean Ariane launch vehicle. Still in service.

19. INSA,)&+ 07.1&.1995

:as aitional ca$abilities such as mobile satellite service business communication an television outreach beyon Inian bounaries. Launche by uro$ean launch vehicle. In service.

&0. INSA,)&D 04.0*.1997 Same as INSA,)&+. Launche by uro$ean launch vehicle Ariane. Ino$erable since ct 4 97 ue to $oer bus anomaly. &1. INSA,)&D, ;anuary

199 !rocure in orbit rom A%A'SA,

&&. INSA,)& 0/.04.1999 <ulti$ur$ose communication = meteorolo"ical satellite launche by Ariane.

&/. INSA,)/' &&.0/.&000

<ulti$ur$ose communication ) business communication evelo$mental communication an mobile communication $ur$ose.

&4. 8SA,)1 1.04.&001 #$erimental Satellite or the irst evelo$mental li"ht o  8eo)synchronous Satellite Launch -ehicle 8SL-)D1.

&5. INSA,)/+ &4.01.&00&

,o au"ment the e#istin" INSA, ca$acity or communication an broacastin" besies $roviin" continuity o the services o INSA,)&+.

&*. >AL!ANA)1 1&.09.&00& <,SA, as the irst e#clusive meteorolo"ical satellite built by IS% name ater >al$ana +hala.

besies $roviin" meteorolo"ical services alon" ith INSA,) & an >AL!ANA)1.

&. 8SA,)& 0.05.&00/ #$erimental Satellite or the secon evelo$mental test li"ht o Inia?s )eos"nc&ronous Sate!!ite Launc& e&ic!e# )SL &9. INSA,)/ &.09.&00/ #clusive communication satellite to au"ment the e#istin"

INSA, System.

/0. D6SA, &0.09.&004 Inia@s irst e#clusive eucational satellite. /1. :A<SA, 05.05.&005

<icrosatellite or $roviin" satellite base Amateur %aio Services to the national as ell as the international community 2:A<s3.

/&. INSA,)4A &&.1&.&005 ,he most avance satellite or Direct)to):ome television broacastin" services.

//. INSA,)4+ 10.07.&00* State)o)the)art communication satellite ) coul not be $lace in orbit.

/4. INSA,)4' 1&.0/.&007

An ientical satellite to INSA,)4A urther au"ment the INSA, ca$acity or Direct),o):ome 2D,:3 television services an other communications.

/5. INSA,)4+% 0&.09.&007

Desi"ne to $rovie Direct),o)home 2D,:3 television services -ieo !icture ,ransmission 2-!,3 an Di"ital Satellite Nes 8atherin" 2DSN83 ientical to INSA,) 4+ .

Inian %emote Sensin" Satellite 2I%S3

/*. I%S)1A 17.0/.19 First o$erational remote sensin" satellite. Launche by a %ussian -osto(.

/7. I%S)1' &9.0.1991 Same as I%S)1A. Launche by a %ussian Launch vehicle -osto(. Still in service.

/. I%S)1 &0.09.199/ +arrie remote sensin" $ayloas. +oul not be $lace in orbit.

/9. I%S)!& 15.10.1994 +arrie remote sensin" $ayloa. Launche by secon evelo$mental li"ht o !SL-.

40. I%S)1+ &.1&.1995 +arries avance remote sensin" cameras. Launche by %ussian <olniya launch vehicle. Still in service.

41. I%S)!/ &1.0/.199*

+arries remote sensin" $ayloa an an )ray astronomy $ayloa. Launche by thir evelo$mental li"ht o !SL-. Still in service.

4&. I%S)1D &9.09.1997 Same as I%S)1+. Launche by Inia?s !SL- service. In service.

4/. I%S)!4 ceansat &*.05.1999

+arries an cean +olour <onitor 2+<3 an a <ulti)reBuency Scannin" <icroave %aiometer 2<S<%3 Launche by Inia@s !SL-)+&

44. ,echnolo"y #$eriment

Satellite 2,S3 &&.10.&001

,echnolo"y #$eriment Satellite Launche by !SL-)+/ .

45. I%S)!* %esourcesat)1 17.10.&00/ Launche by !SL- ) +5 carries three camera names LISS)4 LISS)/ an AiFS

4*. +A%,SA, )1 05.05.&005 Launche by !SL-)+* carries to $anchromatic cameras ) !AN 2ore3 an !AN 2at3 ) ith &.5 meter resolution. ,he cam

mounte ith a tilt o C&* e" an )5 e" alon" the trac( to $rovie stereo ima"es.

47. +A%,SA, ) & 10.01.&007

Launche by !SL-)+7 it is an avance remote sensin" satellite carryin" a $anchromatic camera ca$able o $roviin" scene s$eciic s$ot ima"eries.

4. S% ) 1 10.01.&007

Launche by !SL-)+7 S$ace ca$sule %ecovery #$eriment 2S%)13 intene to emonstrate the technolo"y o an orbitin" $latorm or $erormin" e#$eriments in micro"ravity conitions. S%)1 as recovere successully ater 1& ays over 'ay o 'en"al.

49. +A%,SA,)&A &.04.&00 Ientical to +A%,SA, ) & launche by !SL-)+9

50. I<S)1 &.04.&00 Launche by !SL-)+9 alon" ith +A%,SA,)&A an other  i"ht Nanosatellites

Keplar's Laws of Planetary Motion

Keplar devised three laws which describe the motions of the planets.

Keplar's First Law

Bodies move around the sun in elliptical orbits, with the sun at one focus. The other focus is empty. An ellipse is basically a squashed circle. All bodies orbit in an ellipse, although some are more elliptical than others.

The Earth's average distance from the sun in 1! million "m. #owever, at perihelion1 _{it is 1$% million "m}

from the sun, and at aphelion&_{, 1& million "m. T#e amount which an ellipse deviates from a perfect}

circle can be measured by 'eccentricity'. The Earth has an orbital eccentricity of !.!1 which is relatively circlular. (luto has a much more eccentric orbit, with an eccentricity of !.&, with perihelion and

apthelion of $$!! and $!! million "m respectively.

)f you're loo"ing for loads of fun, the easiest way to construct an ellipse is by ta"ing two drawing pins, stic"ing them into a piece of paper, wrapping a loose piece of string around them, and then using moving a pencil around the loop, "eeping it taught at all times. *ith this method the pins represent the two foci.

Keplar's +irst aw is significant in that most ancient astronomers believed that the planets moved in circular orbits.

Keplars Second Law

The radius vector sweeps out equal areas in equal times.

This states that the line -oining the planet to the sun sweeps the same area in equal times. This means, given Keplar's +irst aw, that planets orbit quic"est when t hey are nearest the sun and the radius vector is smaller, than when they are furthest from the sun.

Keplar's Third Law

This neat relationship was discovered by Keplar before ewton wor"ed out what gravity was. Therefore, Keplar was unable to give a proof. #owever/

Proof:

+udge 1/ Assume the planets have circular orbits

The planets orbit e0periencing a centripetal force towards the un/ +c 2 mv&

3r

*here +c is the centripetal force, m is the planet's mass, r is the planet's distance from the un This centripetal force is provided by t he gravitational force of the un/

+g 2 45m3r&

*here +g is the gravitational force from the un, 4 is the 6niversal gravitational constant and 5 is the mass of the un.

+g 2 +c 27 45m3r& _{2 mv}&_3r 8ancelling m/ 453r&  2 v& 3r 99:1;

)f the planet moves in a circular orbit, then the distance i t moves in a circle is s 2 &<r, and velocity in a circle is distance over time 27 v 2 &<r3T

27 v& _{2 $<}&_r&_3T&

ub into eqn :1; and cancel r's/ 453r& _{2 $<}&_r3T&

5ultiply both sides by T&

r& / 45T&  2 $<& r= 27 T& _{2 $<}&_{345 0 r}= ince $<&

345 is a constant for any central body >eg, the un? 27 T&  _r

∝ =

o he was right, after all.

1 _{The point in the Earth's orbit when it is closest to the sun >helion from helios meaning the sun?} & _{*hen the Earth's furthest from the sun}

Or$ita! E!ements

@igure$

@igure6

Stan%ar% Or$ita! E!ements( Sun or$itin' o$6ect7

8 Ar'ument of *eri&e!ion 8 Eccentricit"

8 Inc!ination

8 Lon'itu%e of t&e Ascen%in' No%e 8 Semi-ma6or a9is of or$it

8 Time of peri&e!ion passa'e

Stan%ar% Or$ita! E!ements( Eart& or$itin' o$6ect7

(#efer to the e<planations below) 8 Ar'ument of *eri'ee

8 Eccentricit" 8 Inc!ination

8 Lon'itu%e of t&e Ascen%in' No%e 8 *erio%

8 Semi-ma6or a9is of or$it 8 Time of peri'ee passa'e T&ese e!ements are usua!!"( (#efer to the e<planations below) 8 Ar'ument of *eri'ee 8 Eccentricit" 8 Epoc& 8 Inc!ination 8 Mean Anoma!" 8 Mean Motion

8 +i'&t Ascension of t&e Ascen%in' No%e Definitions(

J Ar'ument of Latitu%e (not shown)> The geographic latitude of an Earth orbiting satellite at a specific time (the Epoch), e<pressed as an angle measured from the celestial e%uator  northward. J Ascen%in' No%e (A/ in @igure 6)> The point in a satellites orbit where it crosses the plane of the celestial e%uator  (or ecliptic for a sun orbiting obect) going north.

J Ar'ument of *eri'ee *eri&e!ion7> (ω _{in @igure 6) > The angle between the ascending node and}

 perigee (or perihelion for sun orbiting satellites), measured counter clocwise along the plane of the orbit.

J Apo'ee Ap&e!ion7 (@igure $)> oint in orbit when the satellite is farthest from the Earth (sun). J Ce!estia! E.uator( The plane of the Earths e%uator proected onto the celestial sphere. The celestial e%uator is tilted 67.* degrees in relation to the plane of the Earths orbit (the ecliptic). The ecliptic and the celestial e%uator cross at two points, the 'ernal e%uino< and the autumnal e%uino<. J Ce!estia! Sp&ere> A imaginary sphere surrounding the Earth, at some arbitrary great distance, upon which the stars are considered to be fi<ed for the purpose of position measurement. Although it is the Earth that rotates, it appears to an obser'er on the Earth that the Celestial phere re'ol'es around the Earth in one (sidereal) day.

J Eccentricit"# e > Balf of the distance between the foci of an ellipse di'ided by the semi&maor a<is. Thin of it as a measure of how Hout of roundH an ellipse is. An eccentricity of 1 would be a circle.

J Ec!iptic( The plane of the Earths orbit around the sun. The ecliptic is the apparent path of the sun across the celestial sphere o'er the period of one year.

J Ec!iptic Latitu%e( The angle between the position of an astronomical body at the time of interest and the plane of the ecliptic.

J Ec!iptic Lon'itu%e( The angle of an astronomical body from the 'ernal e%uino<, measured EAT along the ecliptic.

J Epoc&( The specific time at which the position of a satellite is specified.

J )eo'rap&ic Lon'itu%e of t&e Ascen%in' No%e (not shown)> The geographic longitude EAT of the rime Meridian where the orbit of an Earth&orbiting satellite crosses the celestial e%uator. :o not confuse with "ongitude of the Ascending /ode.

J Inc!ination, (i in @igure 6)> The angle between the plane of the orbit and the plane of the

celestial e%uator for Earth orbiting satellites (or the plane of the ecliptic for sun orbiting satellites). J Lon'itu%e of t&e Ascen%in' No%e# (Ω _{in @igure 6)> The angle between the 'ernal e%uino< and}

the ascending node, measured counter&clocwise.

JLon'itu%e of *eri'ee (erihelion) The angle between the 'ernal e%uino< and perigee (or perihelion) measured in the direction of the obect5s motion. !t is e%ual to the sum of the Argument of erigee and the "ongitude of the Ascending /ode (Ω _Kω _{in figure 6).}

J Mean Anoma!"> (Compare with True Anomaly) The angle that a satellite would ha'e mo'ed since last passing perigee (or perihelion), assuming that the satellite mo'ed at a constant speed in a orbit on a circle of the same area as the actual orbital ellipse. E%ual to the True Anomaly at perigee and apogee only for elliptical orbits, or at all times for circular orbits.

J Mean Motion( The reciprocal of the eriod, e<pressed in re'olutions per day

J Meri%ian( An imaginary line on the surface of the Earth running from the north pole to the south  pole through any gi'en point on the Earth. Also, an imaginary line on thecelestial sphere running

from the /orth Celestial ole to the outh Celestial pole directly o'er any gi'en point on the Earth. These definitions are essentially the same, one line goes under you feet, one goes o'er your head. The rime Meridian is the meridian the runs through =reenwich, England (1 degrees

longitude).

8 O$!i.uit" of t&e Ec!iptic( The angle between the celestial e%uator  and the ecliptic.

J *eri'ee *eri&e!ion7 (@igure $)> The point in an orbit when the satellite is closest to the Earth (sun).

J *erio%> The time it taes the satellite to complete one orbit.

J +i'&t Ascension( A measure of the angle between the 'ernal e%uino< and a gi'en astronomical obect (star, planet, or satellite), as seen from the Earth. !n astronomy, #ight Ascension (#A) is e<pressed in units of time. The #A is the time that elapses between the transit of the 'ernal e%uino< across any gi'en meridian and the transit of the gi'en obect across the same meridian,

e<pressed in a 68 hour format. #ight Ascension can also be e<pressed as the angle between the 'ernal e%uino< and the obect, measured EAT of the 'ernal e%uino< along the celestial e%uator . J +i'&t Ascension of t&e Ascen%in' No%e Ω _{in @igure 6)> Another term for  "ongitude of the}

Ascending /ode, !t is the angle of the ascending node measured EAT of the 'ernal e%uino< along the celestial e%uator .

J Semi-Ma6or A9is (a in @igure $)> The half of the longer of the two a<es of the orbital ellipse. J Semi-Minor A9is (b in @igure $)> The half of the shorter of the two a<es of the orbital ellipse. J Si%erea! Da"( A sidereal day is the amount of time it taes the Earth to rotate once on it a<is relati'e to the stars. A mean sidereal day is e%ual to 1.+6+ mean solar days, or 67 hours, *0

minutes, 8.$ seconds. The mean solar day and the mean sidereal day differ due to the fact the Earth is orbiting the sun in 70*.6866 mean solar days, resulting in the sun mo'ing slightly across the celestial sphere during one solar day (68 hours)

J Time of *eri'ee *eri&e!ion7 *assa'e( The time at which a satellite last passed perigee (or  perihelion).

J True Anoma!" (θ _{in @igure $)> The actual angle that a satellite has mo'ed since last passing}

 perigee (or perihelion).

J erna! E.uino9( ;ne of two points where the ecliptic crosses the celestial e%uator , the other  being the Autumnal E%uino<. The ?ernal E%uino< is the point where the ecliptic crosses the

celestial e%uator with the sun passing from south to north. Unfortunately for students of astronomy, the same term, ?ernal E%uino<, is used to describe both the ;!/T on the celestial sphere where the crossing occurs (its meaning throughout these e<planations), A/: the M;ME/T !/ T!ME when the crossing occurs (the first moment of spring). Ghich is the intended meaning in any gi'en sentence must be determined by the conte<t on the statement.

Unit II

_{)eostationar" Or$it : Space Se'ment}

)eostationar"

 ;rbit

A'eostationar" orbit is one in which a satellite orbits the earth at e<actly the same speed as the earth turns and at the same latitude, specifically 3ero, the latitude of the e%uator . A satellite orbiting in a geostationary orbit appears to be ho'ering in the same spot in the sy, and is directly o'er the same patch of ground at all times.

A'eos"nc&ronous orbit is one in which the satellite is synchroni3ed with the earths rotation, but the orbit is tilted with respect to the plane of the e%uator. A satellite in a geosynchronous orbit will wander up and down in latitude, although it will stay o'er the same line of longitude. Although the terms geostationary and geosynchronous are sometimes used interchangeably, they are not the same technically2 geostationary orbit is a subset of all possible geosynchronous orbits.

The person most widely credited with de'eloping the concept of geostationary orbits is noted science fiction author Arthur C. Clare (!slands in the y, Childhoods End, #ende3'ous with

#ama, and the mo'ie 611$> a pace ;dyssey). ;thers had earlier pointed out that bodies tra'eling a certain distance abo'e the earth on the e%uatorial plane would remain motionless with respect to the earths surface. 4ut Clare published an article in $8*s Gireless Gorld that made the leap from the =ermans rocet research to suggest permanent manmade satellites that could ser'e as communication relays.

=eostationary obects in orbit must be at a certain distance abo'e the earth2 any closer and the orbit would decay, and farther out they would escape the earths gra'ity altogether. This distance is

7*,+-0 ilometers (66,670 miles) from the surface.

The first geosynchrous satellite was orbited in $07, and the first geostationary one the following year. ince the only geostationary orbit is in a plane with the e%uator at 7*,+-0 ilometers, there is only one circle around the world where these conditions obtain. This means that geostationary real estate is finite. Ghile satellites are in no danger of bumping in to one another yet, they must be spaced around the circle so that their fre%uencies do not interfere with the functioning of their nearest neighbors.

)eostationar" Sate!!ites

There are 6 inds of manmade satellites in the hea'ens abo'e> ;ne ind of satellite ;#4!T the earth once or twice a day, and the other ind is called a communications satellite and it is A#E: in a TAT!;/A#F position 66,711 miles (7*,11 m) abo'e the e%uator of the TAT!;/A#F earth.

A type of the orbiting satellite includes the space shuttle and the international space station which eep a low earth orbit ("E;) to a'oid the deadly ?an Allen radiation belts.

The most prominent satellites in medium earth orbit (ME;) are the satellites which comprise the =";4A" ;!T!;/!/= FTEM or = as it is called.

The =lobal ositioning ystem

The global positioning system was de'eloped by the U.. military and then opened to ci'ilian use. !t is used today to trac planes, ships, trains, cars or literally anything that mo'es. Anyone can buy a recei'er and trac their e<act location by using a = recei'er.

= satellites orbit at a height of about $6,111 miles ($,711 m) and orbit the

About 68 = satellites orbit the earth e'ery $6 hours.

earth once e'ery $6 hours.

These satellites are tra'eling around the earth at speeds of about +,111 mph ($$,611 ph). = satellites are powered by solar energy. They ha'e bacup batteries onboard to eep them running in the e'ent of a solar eclipse, when theres no solar power. mall rocet boosters on each satellite eep them flying in the correct path. The satellites ha'e a lifetime of about $1 years until all their fuel runs out.

)eostationar" Sate!!ites

=eostationary or communications satellites are A#E: in space 66,711 miles (7*,11 m) abo'e the e%uator of the TAT!;/A#F earth. =eostationary satellites are used for weather forecasting, satellite T?, satellite radio and most other types of global communications.

@ig A @ig 4

@ig A Communications satellite in a stationary position or slot  high abo'e the earth.

@ig 4 atellite dish or recei'er installed on a house. These dishes point to a geostationary satellite At e<actly 66,711 miles abo'e the e%uator, the force of gra'ity is cancelled by the centrifugal force of the rotating uni'erse. This is the ideal spot to par a stationary satellite.

At e<actly 66,111 miles (7*,11 m) abo'e the e%uator, the earths force of gra'ity is canceled  by the centrifugal force of the rotating uni'erse.

This is the ideal location to par a stationary satellite. The signal to the satellite is 'ery, 'ery  precise and any mo'ement of the satellite would

cause a loss of the signal.

un outages affect a geostationary satellite

=eostationary satellites are fantastic means of communication e<cept for one little problem called U/ ;UTA=E. These sun outages happen during March and eptember when the sun passes the e%uator. Bere is a %uote from the boo Satellite Technology>

HThe ele'ated temperature of the sun causes it to transmit a high&le'el electrical noise signal to recei'ing systems whene'er it passes behind the satellite and comes within the beams of the

recei'er antennas. The increase in noise is so se'ere that a signal outage usually results. The length and number of the outages depends on the latitude of the earth station and the diameter of the antenna. At an a'erage latitude of 819 in the continental United tates, and a $1&meter antenna, the outages occur o'er 0 days with a ma<imum duration of - minutes each day. Gith a less directional 7&meter antenna, the outages occur o'er $* days, with a ma<imum duration of 68

minutes.H(Satellite Technology, p. $7).

This is ob'iously 'ery embarrassing to the heliocentric people because the sun is not supposed to mo'e. The sun does move howe'er, and twice a year it is o'er the e%uator.

The sun mo'es across the e%uator twice a year gi'ing us the 'ernal (spring) and fall (autumnal) e%uino<es.

J 6 times each year the sun passes the e%uator as it maes it north&south spiral.

J At that time, the sun lies on the celestial e%uator. The word e%uino< refers to the fact that, on this day, the night is e%ual to the day> each is twel'e hours long. The sun is directly abo'e the e%uator, so its rays fall 'ertically down.

J Unfortunately the stationary satellites eclipses the sun and that causes electrical noise or interference to the broadcasting signals.

The esuits forgot to change the dictionaryLL

;b'iously the esuits forgot to change the definition of the word EU!/;D in the English dictionary because it still gi'es the true scientific definition of the word with the sun M;?!/= across the e%uator 6 times each year>

HEither of the two times during a year when the sun crosses the celestial e%uator and when the length of day and night are appro<imately e%ual2 the 'ernal e%uino< or the autumnal

e%uino<.H(Webster's Third New International Dictionary).

anAmats :escription of sun outagesLL :escription

anAmats commercial communications satellites are geostationary, and therefore ha'e orbits that lie near the e%uatorial plane. :uring the spring and fall e%uino<es, the sun also passes close to this  plane. As seen from the ground, the sun seems to pass behind the satellites once per day. :uring

the time when both the satellite and the sun are in the ground stations field of 'iew, the #@ noise energy from the sun can o'erpower the signal from the satellite. !t is this loss or degradation of communications traffic from the satellite that is referred to as sun fade, sun transit or sun outage (see diagram).

The duration of the sun outage depends on se'eral things such as> the beam width or field of 'iew of the recei'ing ground antenna, the apparent radius of the sun as seen from the Earth (about 1.6*9), the #@ energy gi'en off by the sun, the transmitter power of the satellite, the gain and I/  performance of the ground station recei'e e%uipment, along with other factors. All this can affect

whether a ground station will e<perience a complete loss of signal or only a tolerable degradation in signal %uality. The e<act point at which sun outage begins and ends is difficult to determine since it is a gradual transition. The gain of an antenna falls off sharply outside the 7d4 beam width,  but it does not immediately go to 3ero. Therefore, if the sun is ust outside the antennas beam

width, it can still contribute noise and degrade system performance. This maes it difficult to define e<actly what conditions constitute a sun outage.

Bow the program wors

To aid with sun outage predictions, a parameter called outage angle is defined for the ground station. ;utage angle is defined as the ma<imum separation angle (measured from the ground station antenna) between the satellite and the suns center, that results in a sun outage. !n other words, if the separation between the satellite and sun is less than the specified outage angle, then the station is said to be e<periencing a sun outage. ;therwise, the station is not e<periencing a sun outage (see diagram).

tationary satellites need 'ery small motors to eep them in their assigned slotLL

According to the heliocentric theory, the earth is mo'ing at about $,111 mph at the e%uator. !f the geostationary satellites were mo'ing, they would ha'e to mo'e at a speed of about +,111 mph to maintain a stationary orbit abo'e a fi<ed point on the earth. That is about the same speed as the = satellites that orbit the earth twice a day. Bowe'er, = satellites are e%uipped with a rocet engine to maintain their  orbit.

=eostationary satellite diagram. Clic on image to enlarge.

!mage of a = satellite. mall rocet boosters on each satellite eep it flying in the correct path. The satellites ha'e a lifetime of about $1 years until all their fuel runs out.

Spin an% T&ree-A9is Sta$i!i;ation

SpinandThree-AxisStabilization Credits-NASA

Credits-NASA

pin stabili3ation and three&a<is stabili3ation are two methods that are used to orient satellites. Gith spin stabili3ation, the entire spacecraft rotates around its own 'ertical a<is, spinning lie a top. This eeps the spacecrafts orientation in space under control. The ad'antage of spin

stabili3ation is that it is a 'ery simple way to eep the spacecraft pointed in a certain direction. The spinning spacecraft resists perturbing forces, which tend to be small in space, ust lie a gyroscope or a top. :esigners of early satellites used spin&stabili3ation for their satellites, which most often ha'e a cylinder shape and rotate at one re'olution e'ery second. A disad'antage to this type of stabili3ation is that the satellite cannot use large solar arrays to obtain power from the un. Thus, it re%uires large amounts of battery power. Another disad'antage of spin stabili3ation is that the instruments or antennas also must perform NdespinO maneu'ers so that antennas or optical

instruments point at their desired targets. pin stabili3ation was used for /AAs ioneer $1 and $$ spacecraft, the "unar rospector, and the =alileo upiter orbiter.

Gith three&a<is stabili3ation, satellites ha'e small spinning wheels, called reaction wheels or

momentum wheels, that rotate so as to eep the satellite in the desired orientation in relation to the Earth and the un. !f satellite sensors detect that the satellite is mo'ing away from the proper

orientation, the spinning wheels speed up or slow down to return the satellite to its correct position. ome spacecraft may also use small propulsion&system thrusters to continually nudge the

spacecraft bac and forth to eep it within a range of allowed positions. ?oyagers $ and 6 stay in  position using 7&a<is stabili3ation. An ad'antage of 7&a<is stabili3ation is that optical instruments

Station-4eepin' in LEO

tation&eeping is necessary for obects such as the !nternational pace tation, and for satellites for which a precise nowledge of their orbital position is necessary, e.g. earth obser'ation

satellites. The !nternational pace tation has an operational altitude abo'e Earth between 771 and 8$1 m. :ue to atmospheric drag, the space station is constantly losing orbital energy. !n order to compensate for this loss, which would e'entually lead to a reentry of the station, it is being

reboosted to a higher orbit from time to time. The chosen orbital altitude is a trade&off between the delta&' needed to reboost the station and the delta&' needed to send payloads and people to the station. The upper limitation of orbit altitude is due to the constraints imposed by the oyu3

spacecraft. ;n 6* April 611-, the Automated Transfer ?ehicle Hules ?erneH raised the orbit of the ! for the first time, thereby pro'ing its ability to replace (and outperform) the oyu3 at this tas.

Station-4eepin' in )EO

;nce a satellite has reached geostationary orbit, it seems natural that it should remain there. "ife, of course, is not so simple because orbital perturbations cause the satellite to drift.

!nclined orbital planes

The principal correction re%uired is to compensate for /orth&outh drift. The geostationary plane (abo'e the e%uator) is not aligned to the Earths orbit round the un (ecliptic) or the Moons orbit round the Earth, so the gra'itational pull of the un and Moon drags satellites off the plane.

Uncorrected, this would cause the inclination of the orbit to increase by appro<imately one degree  per year. The a'erage annual 'elocity change needed to correct this effect is about *1 mIs, which

can represent *P of the total station&eeping propellant budget.

;ther drift pressures are also significant if uncorrected. East&Gest drift occurs because the e%uator is not perfectly circular, so satellites drift slowly towards one of two longitudinal stable points. olar radiation pressure, caused by the transfer of momentum from the un5s light and infrared radiation, periodically flattens and disturbs the orientation of the orbit. ;ther factors, such as local irregularities in the gra'itational field, also contribute less systematically to drift pressures.

:ue to luni&solar perturbations and the ellipticity of the Earth e%uator, an obect placed in a =E; without any station&eeping would not stay there. !t would start building up inclination at an initial rate of about 1.-* degrees per year. After 60.* years the obect would ha'e an inclination of $* degrees, decreasing bac to 3ero after another 60.* years. Therefore, a lot of energy has to be de'oted to maneu'ers that compensate this tendency. This part of the =E; station&eeping is called /orth&outh control. The ellipticity of the Earth e%uator is causing an East&Gest drift if the satellite is not placed in one of the stable (+* degrees longitude east, $1* degrees longitude west) or unstable ($* degrees longitude west, $0* degrees longitude east) e%uilibrium points.

 /e'ertheless, this part of =E; station&eeping, called East&Gest control re%uires significantly less amount of fuel than /orth&outh control. Therefore, in some cases aging satellites are only East& Gest controlled. This would still guarantee that the satellite is always 'isible to a steerable antenna. Taing into consideration the relati'ely long periods of operation of modern =E; satellites (about $* years) the delta&' e<pended o'er such a period can be substantial (about 80 mIs per year). !t is

therefore crucial for =E; satellites to ha'e the most fuel&efficient propulsion system. ome modern satellites are therefore employing a high specific impulse system lie plasma or ion thrusters.

TT:C Su$s"stem

The TTQC ubsystem contains #adio @re%uency (#@) components, woring in &band, that  pro'ides the necessary functions to ensure atellite access from the =round tation for

commanding and telemetry data transmission. The TTQC ubsystem includes>

• Two &band Transponders2 • Two &band antennas2

• ;ne #adio @re%uency :istribution Unit (#@:U).

The Transponders are connected through the #@:U and #@ coa<ial cables to the two antennas that  pro'ide full spherical co'erage with an o'erlap of at least ten degrees.

The nominal operation scenario foresees that the #ecei'er sections of both Transponders are always switched on.

:epending on the atellite attitude during the =round tation contact, only the Transmitter section of the Transponder connected to the ground&lined antenna is switched on.

;ne Transponder failure can be reco'ered through a cross coupling in the #@:U to allow the connection of the still woring Transponder with both the antennas.

Unit III

_{EA+T< SE)MENT : S*ACE LIN3}