satellite

Satellites are objects that orbit a planet or other body. They can be natural, such as moons, or artificial, manufactured for a purpose and placed into orbit by a launch vehicle. Artificial satellites consist of a payload—the instrument or service they carry—and a spacecraft bus that provides power, propulsion, thermal control, attitude determination, and communications.

Orbits are defined by altitude and shape. Common categories include low Earth orbit (LEO) at about 160 to 2,000 kilometers, medium Earth orbit (MEO), geostationary orbit (GEO) at about 35,786 kilometers, and high Earth orbits (HEO). Polar and sun-synchronous orbits pass over the poles and support Earth observation and climate monitoring.

Satellites support a range of applications, including communications relays, navigation, remote sensing, weather monitoring, scientific research, and military uses. Communications satellites enable television, internet, and phone links; navigation systems provide location data; Earth-observation satellites collect imagery and data on land, oceans, and atmosphere; scientific missions study space and planetary environments.

Launch vehicles place satellites into their target orbits. Once operational, ground stations oversee operations and command the craft remotely. At end of life, satellites may be decommissioned, moved to a graveyard orbit, or deorbited. Space debris and collision risk are managed through tracking and avoidance measures.

The first artificial satellite, Sputnik 1, was launched by the Soviet Union in 1957, inaugurating the space age. Since then, thousands of satellites have been deployed by many nations for civilian, scientific, and military purposes.