Middle French, from Latin satellit-, satelles attendant
- Date: circa 1548
- 1 : a hired agent or obsequious follower : minion, sycophant
- 2 a : a celestial body orbiting another of larger size
- b : a manufactured object or vehicle intended to orbit the earth, the moon, or another celestial body
- 3 : someone or something attendant, subordinate, or dependent; especially : a country politically and economically dominated or controlled by another more powerful country
- 4 : a usually independent urban community situated near but not immediately adjacent to a large city
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon.
The first artificial satellite, Sputnik 1, was launched by the Soviet Union in 1957. By 2010 thousands of satellites have been launched into orbit around the Earth. These originate from more than 50 countries and have used the satellite launching capabilities of ten nations. A few hundred satellites are currently operational, whereas thousands of unused satellites and satellite fragments orbit the Earth as space debris. A few space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Venus, Mars, Jupiter and Saturn.
Satellites are used for a large number of purposes. Common types include military (spy) and civilian Earth observation satellites, communication satellites, navigation satellites, weather satellites, and research satellites. Space stations and human spacecraft in orbit are also satellites. Satellite orbits vary greatly, depending on the purpose of the satellite, and are classified in a number of ways. Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.
Satellites are usually semi-independent computer controlled systems. Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control and orbit control.