Satellites fall into five principal types - research satellites, communication satellites, weather satellites, navigational satellites, and application satellites. Communication satellites provide a worldwide linkup of radio, telephone, and television. The first communication satellite was Echo 1, launched in 1960. Relay 1 and telstar 1 were the first active communications satellites. They were launched in 1962. Telstar 1 transmitted first live television broadcast across the Atlantic.
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Navigational satellites were one of the early applications of artificial earth satellites. Very early in the space age, researchers realized that satellites could be put on orbits to permit ships, aircraft, or other vehicles to exactly determine their locations. Global positioning systems (GPS) make of navigation satellites. The GPS constellation system was first established by the US military to support of their forces. But it is now in widespread in public and commercial applications.
Geostationary satellites are generally placed at an altitude of about 36,000 km. But polar satellites are generally positioned at an altitude of about 850 km, so that they circle the earth every 100 minutes or so.