Communications Satellites have been around since 1958. A communications satellite is a spacecraft that orbits the Earth and relays messages, radio, telephone and television signals. Stations on the ground, called earth stations, transmit signals to the satellite, which then relays the signal to other earth stations. As a newer form of communications, communications satellites are very useful in bringing the people in the world together. Communications between people that used to take days or even months, now take only minutes or seconds using satellites.
The first satellite to relay messages from one Earth Station to another was SCORE (Signal Communicating by Orbiting Relay Equipment) launched December 18, 1958. These early satellites, because they were visible from both sides of the Atlantic Ocean simultaneous for only a short time could provide only a period of five hours a day for communications.
Early United States Satellites
In 1960 the United States launched the Echo satellite, a metallic balloon that reflected signals. Later satellites, such as Telestar and Relay, included electronic relay equipment called transponders. Syncom II, the first satellite to be placed in a synchronous orbit, was launched in 1963. The first commercial communications satellites were launched in 1965.
Passive and Active Communication Satellites
Communications through satellites are either passive or active. The first communications satellites were passive. Signals from Earth were merely reflected from the orbiting metallic sphere. Later types of satellites are active. Active communication satellites receive signals from Earth, electronically strengthen the signals, and transmit the signals to Earth.
Relaying of Signals
This relaying of signals from one Earth Station to another is done through the satellite's transponder. Most communications satellites have more than one transponder and antenna so that they can