Why satellite dishes can point at one fixed spot in the sky
At 35,786 kilometres above the equator, a satellite takes exactly as long to circle Earth as the planet takes to turn, so from the ground it seems to hang still. A science fiction writer championed the idea in 1945; engineers were told it needed too much rocket power.
Such an orbit sits 42,164 kilometres from Earth's centre, runs in the direction of the planet's spin, and matches one sidereal day. The Slovenian engineer Herman Potočnik described it in 1928 as a home for space stations. It first appeared in fiction in a 1942 story by George O. Smith, and in 1945 Arthur C. Clarke laid out how relay stations there could transform global communications.
In 1959 Harold Rosen, an engineer at Hughes Aircraft inspired by Sputnik 1, set out to build one. Transatlantic telephone traffic then relied on shortwave radio and a single undersea cable carrying just 136 calls at once. Most experts thought a satellite that high would cost too much rocket power and not last long enough, so the first efforts went into lower orbits, such as the passive Echo balloons of 1960 and Telstar 1 in 1962, which struggled with weak signals and tracking.
By 1961 Rosen's team had a spinning cylindrical prototype 76 centimetres across that weighed 11.3 kilograms. Syncom 1 failed, but Syncom 2 reached a synchronised though tilted orbit in 1963, and in 1964 Syncom 3 became the first truly geostationary satellite, carrying live pictures of the Tokyo Summer Olympics across the Pacific to America.
Hundreds now serve communications, broadcasting and weather monitoring. Each is launched into a temporary orbit, parked in an assigned slot and nudged regularly to stay put; retired ones are pushed higher into a graveyard orbit. One satellite can see a huge swathe of the planet, and because it never appears to move, ground antennas need no tracking motors. Though most people now have land-based phone and internet links, some remote communities still depend on them.
Source: Geostationary orbit
