Editing Satellite (section)

{{Short description|Objects intentionally placed into orbit}}
{{About|human-made satellites|moons|Natural satellite|other uses|Satellite (disambiguation)}}
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{{Use dmy dates|date=December 2019}}
{{Use American English|date=July 2022}}
[[File:Two 3U CubeSats.jpg|300px|thumb|upright=1.5|alt=Two 3U CubeSats|Two [[CubeSat]]s orbiting around [[Earth]] after being deployed from the ISS [[Kibō (ISS module)|''Kibō'' module]]'s Small Satellite Orbital Deployer]]

A '''satellite''' or an '''artificial satellite'''{{efn|to distinguish them from [[natural satellites]].}} is an object, typically a [[spacecraft]], placed into [[orbit]] around a [[Astronomical object|celestial body]]. They have a variety of uses, including communication relay, [[weather forecasting]], navigation ([[GPS]]), [[broadcasting]], scientific research, and Earth observation. Additional military uses are reconnaissance, [[Early warning system|early warning]], signals intelligence and, potentially, weapon delivery. Other satellites include the final rocket stages that place satellites in orbit and formerly useful satellites that later become defunct.

Except for [[passive satellite]]s, most satellites have an [[electricity generation]] system for equipment on board, such as [[solar panel]]s or [[radioisotope thermoelectric generator]]s (RTGs). Most satellites also have a method of communication to [[ground station]]s, called [[Transponder (satellite communications)|transponders]]. Many satellites use a [[Satellite bus|standardized bus]] to save cost and work, the most popular of which are small [[CubeSat]]s. Similar satellites can work together as groups, forming [[Satellite constellation|constellations]]. Because of the high [[launch cost]] to space, most satellites are designed to be as lightweight and robust as possible. Most communication satellites are radio [[Broadcast relay station|relay stations]] in orbit and carry dozens of transponders, each with a bandwidth of tens of megahertz.

Spaceships become satellites by accelerating or decelerating to reach [[Orbital angular velocity|orbital velocities]], occupying an orbit high enough to avoid [[orbital decay]] due to [[atmospheric drag|drag]] in the presence of an [[atmosphere]] and above their [[Roche limit]]. Satellites are spacecraft launched from the surface into space by [[launch system]]s. Satellites can then change or maintain their orbit by [[Spacecraft propulsion|propulsion]], usually by [[thrusters (spacecraft)|chemical]] or [[ion thruster]]s. As of 2018, about 90% of the satellites orbiting the Earth are in [[low Earth orbit]] or [[geostationary orbit]]; geostationary means the satellites stay still in the sky (relative to a fixed point on the ground). Some imaging satellites choose a [[Sun-synchronous orbit]] because they can scan the entire globe with similar lighting. As the number of satellites and amount of [[space debris]] around Earth increases, the threat of collision has become more severe. An '''orbiter''' is a spacecraft that is designed to perform an [[orbital insertion]], entering orbit around an astronomical body from another,<ref name="d979">{{cite web | title=Definition of ORBITER | website=Merriam-Webster | date=2024-08-05 | url=https://www.merriam-webster.com/dictionary/orbiter | access-date=2025-03-05}}</ref> and as such becoming an artificial satellite. A small number of satellites orbit other bodies (such as the [[Lunar orbit|Moon]], [[Areocentric orbit|Mars]], and the [[Heliocentric orbit|Sun]]) or many bodies at once (two for a [[halo orbit]], three for a [[Lissajous orbit]]).

[[Earth observation satellite]]s gather information for [[Reconnaissance satellite|reconnaissance]], [[Satellite imagery|mapping]], [[Weather satellite|monitoring the weather]], ocean, forest, etc. [[Space telescope]]s take advantage of outer space's [[Ultra-high vacuum|near perfect vacuum]] to observe objects with the entire [[electromagnetic spectrum]]. Because satellites can see a large portion of the Earth at once, [[communications satellites]] can relay information to remote places. The signal delay from satellites and their orbit's predictability are used in [[satellite navigation]] systems, such as GPS. [[Crewed spacecraft]]s which are in orbit or remain in orbit, like [[Space station]]s, are artificial satellites as well.

The first artificial satellite launched into the Earth's orbit was the [[Soviet Union]]'s [[Sputnik 1]], on October 4, 1957. As of December 31, 2022, there are 6,718 operational satellites in the Earth's orbit, of which 4,529 belong to the United States (3,996 commercial), 590 belong to China, 174 belong to Russia, and 1,425 belong to other nations.<ref>{{cite web |url=https://www.ucsusa.org/resources/satellite-database |title=UCS Satellite Database |website=Union of Concerned Scientists |date=1 May 2022 |access-date=30 March 2021 |archive-date=20 December 2019 |archive-url=https://web.archive.org/web/20191220002901/https://ucsusa.org/resources/satellite-database |url-status=live }}</ref>