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. First 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 relay several users of radio waves or signals at the same time. Launch of Communication Satellites
Communications satellites are launched by rockets or carried into space by the Space Shuttle. Once in space, small engines on the satellites guide the satellite into orbit and help keep them there. Most communications satellites are placed in orbit at an altitude of 22,300 miles above the Earth. This is known as a geostationary or synchronous orbit. This allows the satellite to orbit the Earth at the same speed as the rotation of the Earth. As a result, the satellite appears to be stationary above the same location on Earth. Satellite Broadcast Range
Broadcasts from a satellite in synchronous orbit can cover only about one third of the Earth's surface. To send signals anywhere in the world, three communications satellites in geostationary orbit are needed. Communication
Communications satellites will be used to link all the regions and people of the world. This is a giant step from the early uses of communication satellites. "What at the beginning of the decade, was no more than a concept in the minds of a few engineers had, by the end, become a fully commercial system providing global communication system" (Fishlock 23). This global system will consist of many satellites, positioned in geostationary orbit, providing high bandwidth capacity, interconnect many highly specialized Earth Stations operating in more than thirty countries. This network, already in progress by consortiums headed by Motorola (Iridium) will provide the framework and capability for anyone in the world to communicate with anyone else, regardless of location. Telecommunications
The experimental communication satellites were Score, Echo, Telestar, Relay, Syncom. They were all launched by the U.S. between 1958 and 1963. Since then, with the advances in satellite communications, many countries have developed or purchased their own communications satellites, with many others planning to do the same....
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