Communications satellites are used for many different tasks, including television broadcasts and telephone calls. A telephone call made from England to the USA would be sent to the nearest Earth station, which would use its giant antenna to beam the call into space in the form of radio waves. The satellite would receive these radio waves and beam them back down to an antenna on the other side of the planet.
A communications satellite is an artificial satellite that relays and amplifies radio telecommunications signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, internet, and military applications. There are about 2,000 communications satellites in Earth’s orbit, used by both private and government organizations. Many are in geostationary orbit 22,236 miles (35,785 km) above the equator, so that the satellite appears stationary at the same point in the sky, so the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track it.
The high frequency radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points. Communications satellites use a wide range of radio and microwave frequencies. To avoid signal interference, international organizations have regulations for which frequency ranges or “bands” certain organizations are allowed to use. This allocation of bands minimizes the risk of signal interference.
Launched by NASA in 1962, Relay 1 was one of several satellites placed in orbit in the decade after Sputnik to test the possibilities of communications from space. Relay 1 received telephone and television signals from ground stations and then transmitted them to other locations on the Earth’s surface. The satellite relayed signals between North America and Europe and between North and South America, and it also monitored the effects of radiation on its electronics. In conjunction with the Syncom 3 communications satellite, Relay 1 transmitted television coverage of the 1964 Olympics in Japan.
This prototype of Relay 1 is covered with solar cells. The antenna on top is for receiving and transmitting communications signals; those at its base are for telemetry, tracking, and control. In orbit, Relay used spin-stabilization to orient the antennas to communicate with Earth.