satellites

A satellite is an object placed into orbit around a planet or other body to perform a mission. Natural satellites orbit their primaries, with the Moon as the closest example. Artificial satellites are human-made spacecraft launched to gather data, relay signals, observe Earth, navigate, or support science and commerce.

The first artificial satellite, Sputnik 1, was launched by the Soviet Union in 1957, initiating the space age. Since then, thousands of artificial satellites have been placed in orbit, enabling television, weather forecasting, global positioning, climate monitoring, and scientific experiments.

Satellites are built from a bus, which provides structure, power, propulsion, and attitude control, and a payload, which carries the mission instruments. Power is usually supplied by solar panels with onboard batteries; propulsion enables orbit changes; on-board computers run control software and communications.

Orbits are categorized by altitude and shape. Low Earth Orbit (LEO) ranges from about 160 to 2,000 km; Medium Earth Orbit (MEO) covers roughly 2,000 to 35,786 km; Geostationary Orbit (GEO) sits at 35,786 km and keeps a satellite fixed over a point on the equator. Highly elliptical orbits (HEO) are used for specialized missions.

Operational satellites require ground control, tracking, and collision avoidance. End-of-life planning is important to reduce space debris, with options including deorbiting, moving to a graveyard orbit, or ensuring safe disposal. Large constellations, such as those used for broadband, demonstrate modern scalability and connectivity.