Editing Geosynchronous orbit (section)

=== Geostationary orbit ===
{{main|Geostationary orbit}}
[[File:Geostat.gif|thumb|The geostationary satellite (green) always remains above the same marked spot on the equator (brown).]]
A geostationary equatorial orbit (GEO) is a circular geosynchronous orbit in the plane of the Earth's equator with a radius of approximately {{convert|42164|km|mi|0|abbr=on}} (measured from the center of the Earth).<ref name="smad"/>{{rp|156}} A satellite in such an orbit is at an altitude of approximately {{convert|35786|km|mi|0|abbr=on}} above mean sea level. It maintains the same position relative to the Earth's surface. If one could see a satellite in geostationary orbit, it would appear to hover at the same point in the sky, i.e., not exhibit [[diurnal motion]], while the Sun, Moon, and stars would traverse the skies behind it. Such orbits are useful for [[telecommunications satellite]]s.<ref>{{cite web|url=https://www.esa.int/Our_Activities/Telecommunications_Integrated_Applications/Orbits |title=Orbits |publisher=[[ESA]] |access-date=October 1, 2019 |date=October 4, 2018}}</ref>

A perfectly stable geostationary orbit is an ideal that can only be approximated. In practice the satellite drifts out of this orbit because of perturbations such as the [[solar wind]], [[radiation pressure]], variations in the Earth's gravitational field, and the [[gravity|gravitational]] effect of the [[Moon]] and [[Sun]], and thrusters are used to maintain the orbit in a process known as [[orbital station-keeping|station-keeping]].<ref name="smad">{{cite book|title=Space Mission Analysis and Design|publisher=Microcosm Press and Kluwer Academic Publishers |editor1-first=Wiley J. |editor1-last=Larson |editor2-first=James R. |editor2-last=Wertz |bibcode=1999smad.book.....W |last1=Wertz |first1=James Richard |last2=Larson |first2=Wiley J. |year=1999|isbn=978-1-881883-10-4}}</ref>{{rp|156}}

Eventually, without the use of thrusters, the orbit will become inclined, oscillating between 0° and 15° every 55 years. At the end of the satellite's lifetime, when fuel approaches depletion, satellite operators may decide to omit these expensive manoeuvres to correct inclination and only control eccentricity. This prolongs the life-time of the satellite as it consumes less fuel over time, but the satellite can then only be used by ground antennas capable of following the N-S movement.<ref name="smad"/>{{rp|156}}

Geostationary satellites will also tend to drift around one of two stable longitudes of 75° and 255° without station keeping.<ref name="smad"/>{{rp|157}}