Editing Geosynchronous orbit (section)

== Types ==

=== 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}}

=== Elliptical and inclined geosynchronous orbits ===

[[File:Qzss-45-0.09.jpg|left|thumb|A quasi-[[zenith]] satellite orbit]]

Many objects in geosynchronous orbits have eccentric and/or inclined orbits. Eccentricity makes the orbit elliptical and appear to oscillate E-W in the sky from the viewpoint of a ground station, while inclination tilts the orbit compared to the equator and makes it appear to oscillate N-S from a groundstation. These effects combine to form an [[analemma]] (figure-8).<ref name="smad"/>{{rp|122}}

Satellites in elliptical/eccentric orbits must be tracked by steerable [[ground station]]s.<ref name="smad"/>{{rp|122}}

====Tundra orbit====
{{main|Tundra orbit}}

The Tundra orbit is an eccentric geosynchronous orbit, which allows the satellite to spend most of its time dwelling over one high latitude location. It sits at an inclination of 63.4°, which is a [[frozen orbit]], which reduces the need for [[orbital station-keeping|stationkeeping]].<ref name="scs">{{cite book|url=https://books.google.com/books?id=PEsmLaDXzvsC&q=tundra&pg=PT110 |section=2.2.1.2 Tundra Orbits |isbn=978-1-119-96509-1 |title=Satellite Communications Systems: Systems, Techniques and Technology|last1=Maral |first1=Gerard |last2=Bousquet |first2=Michel |date=2011-08-24|publisher=John Wiley & Sons }}</ref> At least two satellites are needed to provide continuous coverage over an area.<ref name="jenkin">{{cite conference|title=Tundra Disposal Orbit Study |surname1=Jenkin |given1=A.B. |surname2=McVey |given2=J.P. |surname3=Wilson |given3=J.R. |surname4=Sorge |given4=M.E. |date=2017 |publisher=ESA Space Debris Office|conference=7th European Conference on Space Debris|url=https://conference.sdo.esoc.esa.int/proceedings/sdc7/paper/328|access-date=2017-10-02|archive-url=https://web.archive.org/web/20171002121240/https://conference.sdo.esoc.esa.int/proceedings/sdc7/paper/328|archive-date=2017-10-02|url-status=dead}}</ref> It was used by the [[Sirius XM Satellite Radio]] to improve signal strength in the northern US and Canada.<ref name="Sirius Launch">{{cite web
  | title=Sirius Rising: Proton-M Ready to Launch Digital Radio Satellite Into Orbit
  | url=http://www.americaspace.com/2013/10/18/sirius-rising-proton-m-ready-to-launch-digital-radio-satellite-into-orbit/
  | website=AmericaSpace
  | access-date=8 July 2017
  | date=2013-10-18
  | archive-url=https://web.archive.org/web/20170628043459/http://www.americaspace.com/2013/10/18/sirius-rising-proton-m-ready-to-launch-digital-radio-satellite-into-orbit/
  | archive-date=28 June 2017
  | url-status=live
  }}</ref>

====Quasi-zenith orbit====
The [[Quasi-Zenith Satellite System]] (QZSS) is a four-satellite system that operates in a geosynchronous orbit at an inclination of 42° and a 0.075 eccentricity.<ref>{{citation |title=Interface Specifications for QZSS |version=version 1.7 |url=http://qz-vision.jaxa.jp/USE/is-qzss/index_e.html |date=2016-07-14 |author=Japan Aerospace Exploration Agency |pages=7–8 |url-status=dead |archive-url=https://web.archive.org/web/20130406032030/http://qz-vision.jaxa.jp/USE/is-qzss/index_e.html |archive-date=2013-04-06}}</ref> Each satellite dwells over [[Japan]], allowing signals to reach receivers in [[urban canyons]] then passes quickly over Australia.<ref>{{cite web |url=http://qzss.go.jp/en/technical/technology/orbit.html |title=Quasi-Zenith Satellite Orbit (QZO) |access-date=2018-03-10 |archive-url=https://web.archive.org/web/20180309194252/http://qzss.go.jp/en/technical/technology/orbit.html |archive-date=2018-03-09 |url-status=live}}</ref>