The Clarke orbit reference article from the English Wikipedia on 24-Apr-2004
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Clarke orbit

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More commonly known as geosynchronous orbits and geostationary orbits, these were first popularised by science fiction author Arthur C. Clarke in 1945 as useful orbits for communications satellites, Clarke orbits are 35,790 kilometers above the Earth and have a period of 24 hours, exactly matching the rotation of the Earth. Seen from the surface of the Earth, a satellite in such an orbit appears motionless, thus an antenna can point in a fixed direction and maintain a link with the satellite. The first communications satellite placed in a Clarke orbit was Syncom 2, launched in 1963. Clarke orbits have been in common use ever since.

See also