The Physics Factbook
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website
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|Cutnell, John & Kenneth W., Johnson. Physics. New York: Wiley, 1998: 148.||"What is the height above the earth's surface at which all synchronous satellites must be placed in orbit?"||35,887 km|
|Elbert, Bruce. The Satellite Communication Applications Handbook. MA: Artech House, 1997: 361.||"At 36,000 km, the GEO approach to a global MSS system allows the service to be implemented with only three satellites."||36,000 km|
|Abrishamkar, Farrokh & Zoran, Siveski. PCS Global Mobile Satellites. IEEE Communications Magazine, 1996.||"The GEOs, which are seen as stationary from earth, in principle require three satellites (at an altitude of about 35,800 km) to provide complete uninterrupted global coverage."||35,800 km|
|Syncom 2. NSSDC Master Catalog: Spacecraft. National Space Science Data Center (NASA), 3 January 2001.||"Syncom 2 was launched into high altitude orbit from Cape Canaveral on July 26, 1963. Six hours after launch the apogee motor was fired to place the spacecraft in an orbit ranging from 34,100 to 36,440 km with a drift rate of 7.5 degrees per day eastward"||(34,100-36,440 km)|
|Spangenburg, Ray & Rit, Moser. Artificial Satellites. New York: Grolier, 2001.||"Geosynchronous Satellites, including broadcast, communications, data relay, surveillance, and weather observation. (21,750 to 22,370 mi)."||(35,000-36,000 km)|
A satellite is an object that orbits around another object in space. Artificial satellites are man-made robots that are purposely placed into orbit around Earth by rocket launchers or shuttle crews. These satellites perform numerous tasks in communication industry, military intelligence and scientific studies both Earth and space.
In 1960, Hughes Space and Communication Company along with RCA and AT&T urged NASA to develop a different type of satellite. Dr. Harold Rosen and his team decided to place a communication satellite in geostationary orbit, this orbit would keep the satellite over the same spot above Earth's equator providing the effective platform that is necessary to send out radio signals from a point on the ground. Syncom I was launched in 1963, but it stopped sending signals a few seconds before it reached its final orbit. Syncom II was launched five months later demonstrating viability of the system. The third Syncom transmitted live coverage of the Olympic Games in Tokyo to stations in North America and Europe.
Communication satellites provide communication over long distances by reflecting or relaying radio-frequency signals. From point-to-point high capacity trunk communications between large costly ground terminals has emerged to multipoint-to-multipoint communications between small, low cost stations. By reusing frequency which in turn allows satellites to communicate with number of ground stations using the same frequency by transmitting in narrow beams pointed towards each of the stations. Adjustments can be made to beam widths to cover large areas as big as entire US or small as a state. Stations apart far enough receive different messages transmitted on the same frequency.
Geosynchronous satellites which orbit Earth 35,900 km (22,300 miles) above the ground, offer the best locations because the high orbit allows satellites orbital speed to match the rotation speed of Earth and remain essentially stable over the same spot.
Alexandra Kravtsova -- 2004
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