Satellite Communication Notes

Department of ECE Lecture Notes EC1015 - SATELLITE SATELLITE COMMUNICATION

Unit I

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

Communication Sate!!ite(-

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  low polar Earth orbits. They are also used for mobile applications such as communications to ships and plan planes es,, for for whic which h appl applic icat atio ion n of other other tech techno nolo logi gies es,, such such as cabl cable, e, are are impr imprac acti tical cal or  impossible.

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

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Ear!" Missions(The first satellite e%uipped with on&board radio radio&&transmitters transmitters was  was the o'iet putni $, launched in $*+. The first American satellite to relay communications was proect score in $*$*-,, which used a tape recorder to store and forward 'oice forward 'oice messages. !t was used to send a Christmas greeting to the world from resident Eisenhower .  /AA launched  /AA  launched an Echo satellite in $01 $0122 the $11&foot $11&foot alumini3ed alumini3ed ET film balloon film balloon ser'ed as a  passi'e reflector for radio communications. Courier $4, (built by hilco hilco)) also launched in $01, was the world5s first acti'e repeater satellite. Telstar Telstar was the first acti'e, direct relay communications satellite. !t was placed in an elliptical orbit (completed once e'ery 6 hours and 7+ minutes), rotating at a 8*9 angle abo'e the e%uator . The first truly geostationary satellite launched in orbit was the yncom 7, launched on August $, $, $08. !t was placed in orbit at $-19 east longitude longitude,, o'er the !nternational :ate "ine. "ine. !t was used that same year to relay tele'ision co'erage on the $08 ummer ;lympics in ;lympics in Toyo Toyo to  to the United tates,, the first tele'ision transmission sent o'er the acific ;cean. tates hortly after yncom 7, 7, !ntelsat !, !, aa Early 4ird, was launched on April 0, 0, $0* and placed in orbit at 6-9 west longitude. !t was the first geostationary satellite for telecommunications o'er the Atlantic ;cean. ;cean.

)eostationar" Sate!!ites(A satellite in a geostationary orbit appears orbit appears to be in a fi (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 A imaginary sphere surrounding the Earth, at some arbitrary great distance, upon which the stars are considered to be fi The half of the longer of the two a The half of the shorter of the two a 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