Also known as a geostationary satellite, a satellite in an orbit which matches the rotation of the earth, resulting in a stationary appearance from the planet's surface.
At an altitude of 22,300 miles, geosynchronous satellites take exactly one day to orbit the earth, and therefore appear to hover over one spot above the equator. Receiving and transmitting antennae on the earth do not need to track such a satellite, are fixed in place and are much less expensive than tracking antennae. They have revolutionized global communications, positioning, navigation and television broadcasting.
The concept was first proposed by the science fiction author Arthur C. Clarke around 1945. Working prior to the advent of solid-state electronics, Clarke envisioned a trio of large, manned space stations arranged in a triangle around the planet. Modern satellites are numerous, unmanned, and are often no larger than an automobile.
One disadvantage of geosynchronous satellites is a result of their high alititude: radio signals take a fraction of a second to reach and return from the satellite, resulting in a small signal delay.