Communication satellites. Computer illustration of communication satellites in space orbiting above the Earth. Each satellite has solar cell arrays (blue) to produce power, and a rounded dish antenna to receive and transmit communication signals. These satellites act as relay vehicles for radio signals. Typical communication satellites orbit with the same period as the rotation of the Earth at a height of 35,700 kilo- metres. In this geostationary orbit each satellite appears to 'hover' above the same point at all times. These satellites are used to relay telephone and fax messages, computer data, and to broadcast television signals.