Outline of artificial satellites

Artificial satellites are human-made spacecraft placed into orbit around Earth or another celestial body. They are distinct from natural satellites such as moons, and from space probes that travel beyond Earth orbit or between planetary bodies. Artificial satellites operate as part of wider satellite systems that may include a satellite bus, payload, ground segment, launch vehicle, tracking network, and regulatory framework. Artificial satellites are used for communications, navigation, Earth observation, weather monitoring, scientific research, military support, intelligence gathering, astronomy, and technology demonstration. They occupy many types of orbits, including low Earth orbit, medium Earth orbit, geostationary orbit, Sun-synchronous orbit, polar orbit, highly elliptical orbit, Lagrange-point orbits, and orbits around the Moon, Mars, and other Solar System bodies.

Essence of satellites

Artificial satellites are spacecraft placed in orbit to perform functions through a payload, supported by a satellite bus, ground segment, and wider satellite systems. Satellites are defined by their primary body, their orbital motion, and their distinction from natural satellites, space probes, space stations, orbital debris, and other kinds of spacecraft. Satellites make up the vast majority of modern space missions and launches.

Basic satellite functions

Communications Communications satellite – Artificial satellite that relays radio signals. Telecommunications – Transmission of information electromagnetically. Tracking and data relay satellite – American communications satellite. Military support Early warning satellite – Ballistic missile detection satellite. Military communications – Messages within armed forces. Military satellite – Artificial satellite used for military purposes. Reconnaissance satellite – Satellite that covertly collects data for intelligence or military applications. Navigation Geopositioning – Determination of the geographic position of an object. Global navigation satellite system - Satellites that provide signals for geopositioning. Satellite navigation – Use of satellite signals for navigation or geo-spatial positioning. Observation Remote sensing – Obtaining information through non-contact sensors. Earth observation satellite – Satellite designed to observe Earth from orbit. Satellite imagery – Images taken from an artificial satellite. Scientific measurement Space physics – Study of space plasmas in the Solar System. Space telescope – Instrument in space to study astronomical objects. Technology demonstration CubeSat – Miniature satellite in 10 cm cube modules. Technology demonstration satellite – Showcasing an idea for new technology. Timing Precise Time and Time Interval – Standard for highly accurate timing information. Time and frequency transfer – Scheme where multiple sites share a precise reference time or frequency.

Core concepts Artificial satellite Satellite – Objects intentionally placed into orbit Sputnik 1 – First artificial Earth satellite Orbit Kepler's laws of planetary motion – Laws describing planetary orbits Orbit – Curved path of an object around a point Orbital mechanics – Field of classical mechanics concerned with the motion of spacecraft Orbital period – Time an astronomical object takes to complete one orbit around another object Payload Payload – Carrying capacity of a vehicle Satellite bus – Main body and structural component of the satellite Primary body Barycenter – Center of mass of multiple bodies orbiting each other Primary body – Prime astronomical designated entity within a gravitational system

Satellite Satellite – Objects intentionally placed into orbit Artificial satellite – Objects intentionally placed into orbit List of natural satellites Natural satellite – Astronomical body that orbits a planet

Satellite system

Ground segment – Ground-based elements of a spacecraft system Satellite constellation – Group of artificial satellites working together as a system Spacecraft Spacecraft – Vehicle or machine designed to fly in space Spacecraft design Uncrewed spacecraft – Spacecraft without people on board

Fundamental distinctions Natural and artificial satellites Artificial satellite – Objects intentionally placed into orbit Moon – Natural satellite orbiting Earth Natural satellite – Astronomical body that orbits a planet Satellites and orbital debris Derelict spacecraft – Pollution around Earth by defunct artificial objects Graveyard orbit – Spacecraft end-of-life orbit Kessler syndrome – Theoretical satellite collision cascade Orbital debris – Pollution around Earth by defunct artificial objects Space debris – Pollution around Earth by defunct artificial objects Satellites and space probes Flyby (spaceflight) – Flight event at some distance from the object Interplanetary probe – Unmanned robotic spacecraft Spacecraft – Vehicle or machine designed to fly in space Space probe – Unmanned robotic spacecraft Satellites and space stations International Space Station – Modular space station in low Earth orbit Mir – Soviet/Russian space station (1986–2001) Skylab – First space station launched and operated by NASA (1973–1979) Space station – Habitable artificial satellite Tiangong space station – Chinese modular space station (since 2021) Satellites and spacecraft Crewed spacecraft – Spacecraft with life-support systems Robotic spacecraft – Spacecraft without people on board Spacecraft – Vehicle or machine designed to fly in space Uncrewed spacecraft – Spacecraft without people on board

Applications Artificial satellites are used across civil, commercial, scientific, and military fields. Major applications include astronomy, communications, Earth observation, remote sensing, satellite navigation, weather monitoring, military support, and educational or amateur spaceflight.

Astronomy and space science

Satellites support astronomy and space science by carrying instruments above Earth's atmosphere, observing wavelengths and environments that are difficult or impossible to study from the ground. Major scientific uses include space telescope observations, cosmic microwave background mapping, gamma-ray astronomy, infrared astronomy, X-ray astronomy, planetary science, solar observation, and space physics.

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