Geostationary Orbit Military Satellite
A geostationary orbit (GEO) is an orbit directly above the Earth’s equator (0º latitude). It is a special case of the geosynchronous orbit (abbreviated GSO), and is the one which is of most interest to operators of artificial satellites (including communication and television satellites). Satellite locations may differ by longitude only as geostationary orbits must have a latitude that is zero.
The idea of a geosynchronous satellite for communication purposes was first published in 1928 by Herman Potočnik. The geostationary orbit was first popularised by science fiction author Arthur C. Clarke in 1945 as a useful orbit for communications satellites. As a result this is sometimes referred to as the Clarke orbit. Similarly, the Clarke Belt is the part of space approximately 35,786 km above mean sea level in the plane of the equator where near-geostationary orbits may be achieved.
Geostationary orbits are useful because they cause a satellite to appear stationary with respect to a fixed point on the rotating Earth. As a result, an antenna can point in a fixed direction and maintain a link with the satellite. The satellite orbits in the direction of the Earth’s rotation, at an altitude of approximately 35,786 km (22,240 statute miles) above ground. This altitude is significant because it produces an orbital period equal to the Earth’s period of rotation, known as the sidereal day.