Introduction A satellite is an object that orbits or revolves around another object. For example, the Moon is a satellite of Earth, and Earth is a satellite of the Sun. They are highly specialized wireless receiver/transmitters that are launched by a rocket and placed in orbit around the Earth.

NEED OF SATELLITE COMMUNICATION In early 1960’s, the American Telephone n Telegraph Company (AT&T) released studies indicating that a few powerful satellites of advanced design could handle more traffic than the entire AT&T long-distance communication network. The cost was also not too much with respect to long-distance communication network. Satellite systems offer more flexibility then submarine cables, buried underground cables, line-of-sight microwave radio or optical fiber systems.

SATELLITE A body which revolves around another body of preponderant mass and which has a motion primarily and permanently determined by the force of attraction of that other body. OR a satellite is any object that orbits or revolves around another object. For example, the Moon is a satellite of Earth, and Earth is a satellite of the Sun.

SATELLITE COMMUNICATION A satellite communications system uses satellites to relay radio transmissions between earth terminals. A telecommunications service provided via one or more satellite relays and their associated uplinks and downlinks.

UPLINK & DOWNLINK FREQUENCIES A typical operational link involves an active satellite and two or more earth terminals. One station transmits to the satellite on a frequency called the UP-LINK frequency (6 or 14GHz). The satellite then amplifies the signal, converts it to the DOWN-LINK frequency (4 or 12GHz), and transmits it back to earth. The signal is next picked up by the receiving terminal.

SATELLITE ELEMENTS There are 2 parts common to all satellites, they are, Payload & The bus

HISTORY OF SATELLITES 1956 First Trans-Atlantic Telephone Cable: TAT-1 1957 Sputnik: Russia launches the first earth satellite. 1960 1st Successful DELTA Launch Vehicle 1961 Formal start of TELSTAR, RELAY, and SYNCOM Programs 1962 TELSTAR and RELAY launched 1963 SYNCOM launched 1964 INTELSAT formed 1965 COMSAT's EARLY BIRD: 1969 INTELSAT-III series provides global coverage 1972 ANIK: 1st Domestic Communications Satellite (Canada) 1974 WESTAR: 1st U.S. Domestic Communications Satellite 1975 INTELSAT-IVA: 1st use of dual-polarization 1975 RCA SATCOM: 1st operational body-stabilized comm. satellite 1976 MARISAT: 1st mobile communications satellite 1976 PALAPA: 3rd country (Indonesia) to launch domestic comm. satellite 1979 INMARSAT formed. 1988 TAT-8: 1st Fiber-Optic Trans-Atlantic telephone

TYPES OF SATELLITE Passive Satellite. Active Satellite.

PASSIVE SATELLITE A satellite that only reflects signals from one Earth station to another, or from several Earth stations to several others. OR An Earth satellite intended to transmit radio communication signals by reflection.

ACTIVE SATELLITE A satellite carrying a station intended to transmit or retransmit radio communication signals. It performs signal processing functions such as amplification, regeneration, frequency translation, and link switching, to make the signals suitable for retransmission. Sputnik1 was the first active satellite launched.

GEOSTATIONARY SATELLITE Geostationary satellites r satellites that orbit in a circular pattern with an angular velocity equal to that of earth. they remain in a fixed position in respect to a given point on earth and available to all earth stations withi their shadow 100% of the time They require sophisticated and heavy propulsion devices on board to keep them in a fixed orbit. Syncom I launched in feb 1963, was the first attempt then ,SyncomII, syncomIII

FOOTPRINTS The area on Earth that geo satellites can "see" is called the satellite's "footprint." Here is one footprint that covers all of Africa. A person in Africa can use this satellite to communicate with anyone else in Africa. We can also use satellites as a relay system to send signals anywhere on Earth. Here you can see the overlapping footprints of four different satellites. If you wanted to send a signal from Africa to Southeast Asia, you could bounce, or relay, the signal using more than one satellite.

TYPES OF ORBITS LEO POLAR GEO ELLIPTICAL

LOW EARTH ORBIT When a satellite circles close to Earth we say it's in Low Earth Orbit (LEO) Satellites in LEO are just 200 - 500 miles high. B/c they orbit so close to Earth, they must travel very fast so gravity won't pull them back into the atmosphere. Satellites in LEO speed along at 17,000 miles per hour. They can circle Earth in about 90 minutes.

A Low Earth Orbit is useful because its nearness to Earth. can capture very detailed images of Earth's surface.

POLAR ORBIT A Polar orbit is a particular type of Low Earth Orbit. The only difference is that a satellite in polar orbit travels a north-south direction, rather than the more common east-west direction. Polar orbits are useful for viewing the planet's surface weather satellites, are almost always in polar orbit. No other orbit gives such thorough coverage of Earth.

GEOSYNCHRONOUS EQUATORIAL ORBIT A satellite in geosychonous equatorial orbit (GEO) is located directly above the equator, exactly 22,300 miles out in space. a satellite in GEO always stays directly over the same spot on Earth.

ELLIPTICAL ORBIT A satellite in elliptical orbit follows an oval-shaped path. One part of the orbit is closest to the center of Earth (perigee) and the other part is farthest away (apogee). A satellite in this orbit takes about 12 hours to circle the planet. Like polar orbits, elliptical orbits move in a north-south direction