David Causey, age 12, of New Market, Ala., for his question:
PLEASE EXPLAIN COMMUNICATION SATELLITES
First person to suggest using satellites for communication was an English writer by the name of Arthur Clarke. He suggested in 1945 that manned satellites be located in synchronous orbits above the earth. In 1955 an American scientist named John Robinson Pierce suggested using unmanned passive and active satellites. The system was working in 1958.
Radio, telephone, television and other electronic communications to any part of the world can now be accomplished because of the communications satellites that are traveling in space.
Launched into orbits around the earth by rockets, the satellites receive signals transmitted from stations on the ground and then by means of special antennas they send the signals back to earth.
Communication by satellite is more reliable than short wave radio and it also has better quality. The signals can be picked up by stations that may be as far as a third of the way around the world.
Passive communications satellites simply reflect signals as a mirror would reflect light. America's first passive communications satellite was called Echo. The 100 foot plastic balloon was launched in 1960. Echo II was launched in 1964.
Active communications satellites carry radio receivers and transmitters. They pick up signals from earth and then strengthen them by amplification and transmit them back to earth. Most active satellites are less than 10 feet high and receive their power from the sun by using solar batteries.
Television shows and telephone messages are relayed regularly from North America to Europe and back. Satellites include the Telstar, Relay and Syncom, all launched during the 1960s.
The first commercial communications satellite, launched by a company called COMSAT, was the Early Bird or INTELSAT I, an active satellite launched in 1965. It has 240 telephone channels as well as television broadcasting abilities. INTELSAT II, III and IV were launched later and now both the Atlantic and Pacific are covered. Viewers in North America can now watch live television from Europe, Hawaii, Japan, the Philippines or Thailand.
Synchronous satellites are launched to an altitude of 22,300 miles. Located at this altitude, they become synchronized with the earth's rotation and make one complete orbit every day. Three such satellites, properly placed, can link any two stations in the world.
Our satellites have low power transmitters and large ground antennas are needed to receive their signals. Future satellites have been proposed with more power so that signals will be able to go directly into small housetop antennas. DirecTV transmits directly into homes.