GEOSYNCHRONOUS SATELLITES AND TELEVISION

by

R. J.. Reiman, Historian

Arthur C. Clarke, distinguished Engineer and science fiction author, conceived the principle of geosynchronous satellites and for their use for transmission and distribution of communications signals, including radio and television. He was born in Minehead, Somerset, England in 1927. During World War II, he was an officer with the Royal Air Force working with engineers from MIT in England on ground control approach for aircraft landings under restricted visibility. During this period, he proposed the concept of geosynchronous satellites in a publication "Wireless World" in October 1945. Based on the success of Germany's V-2 rocket, a rocket could conceivably be developed which could put a communication satellite in geosynchronous orbit, 22,300 miles above the earth. and he calculated the rocket's velocity, orbital plane, height to be reached, and predicted the geographic coverage or "footprint" that a satellite could cover. He proposed a solar-power supply, the radio-frequency power required to communicate with earth stations, and further predicted manned space stations. He also foresaw problems during solar eclipses with communications.

The first communications satellite, "Sputnik", launched by USSR in 1957, weighed 100 pounds, traveled in a low orbit, but caused consternation in the US. Spurred by this competition, the US Air Force launched "Score" in 1958, followed by the first two-way communications satellite, "Echo", in 1960, a one hundred foot diameter reflecting sphere, followed by "Courier l". Also non-synchronous was AT&T's "Telestar l" in 1962, which could only be used as it passed over the communications area. After the Delta #3914 rocket was developed in 1963, NASA launched the "Syncom" geosynchronous satellites, followed by the "Intelstat" series in 1967-71, for international communications. Attempts to use the Space Shuttle for satellite launching has been a mixed success.

FM is used for the satellite transmission since it does not require highly linear amplifiers, has advantages over AM in noise improvement and the transmission energy can be uniformly distributed across the channel bandwidth. The satellites have antennae for both sending and receiving, are equipped with transponders to both amplify the received ground signal and to shift it to another frequency for transmission, and are solar-powered, with batteries to ride through periods during eclipses. The satellite is equipped to maintain proper orbit, by use of ejecting hydrozene gas in rocket fashion, to position or "station keep" its position. Earth Stations vary from expensive and complicated satellite communications carriers to simple back-yard receiving stations, Round, dish-shaped antennas, that focus the energy in a narrow beam are used, and must be located so as not to interfere with microwave signals.

Satellite use has grown in both national and international radio, telephone and television communications, with increasing regulations needed in areas such as frequency allocation, bandwidth and clearance with microwave signals. The problem of maintaining satellites in orbit has deterred progress, with many of NASA's troubles with the shuttle, and its concentration on manned programs, and absence of reliable disposable rockets.