An earth station, ground station, or earth terminal is a terrestrial terminal station designed for extraplanetary telecommunication with spacecraft, and/or reception of radio waves from an astronomical radio source. Earth stations are located either on the surface of the Earth, or within Earth’s atmosphere. Earth stations communicate with spacecraft by transmitting and receiving radio waves in the super high frequency or extremely high frequency bands (e.g., microwaves). When an earth station successfully transmits radio waves to a spacecraft (or vice versa), it establishes a telecommunications link.
Earth stations may occupy either a fixed or itinerant position. Article 1 § III of the ITU Radio Regulations describes various types of earth stations, stationary and mobile, and their interrelationships.
Specialized satellite earth stations are used to telecommunicate with satellites—chiefly communications satellites. Other earth stations communicate with manned space stations or unmanned space probes. An earth station that primarily receives telemetry data, or that follows a satellite not in geostationary orbit, is called a tracking station.
When a satellite is within an earth station’s line of sight, the earth station is said to have a view of the satellite. It is possible for a satellite to communicate with more than one earth station at a time. A pair of earth stations are said to have a satellite in mutual view when the stations share simultaneous, unobstructed, line-of-sight contact with the satellite.