Editing Satellite navigation (section)

{{short description|Use of satellite signals for geo-spatial positioning}}
{{For|maneuvering satellites to maintain orbit and station|Orbital station-keeping}}
[[File:GPS Block IIIA.jpg|thumb|The [[U.S. Space Force]]'s [[Global Positioning System]] was the first global satellite navigation system and the first to be provided as a free global service.]]
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A '''satellite navigation''' or '''satnav''' system is a system that uses [[satellite]]s to provide autonomous [[geopositioning]]. A satellite navigation system with global coverage is termed '''global navigation satellite system''' ('''GNSS'''). {{As of|2024}}, four global systems are operational: the [[United States]]'s [[Global Positioning System]] (GPS), [[Russia]]'s Global Navigation Satellite System ([[GLONASS]]), [[China]]'s [[BeiDou]] Navigation Satellite System (BDS),<ref name=autogenerated1>{{cite web|url=https://www.cnn.com/2020/06/24/tech/china-beidou-satellite-gps-intl-hnk/index.html |title=China's GPS rival Beidou is now fully operational after final satellite launched |date=24 June 2020 |publisher=cnn.com |access-date=2020-06-26}}</ref> and the [[European Union|European Union's]] [[Galileo (satellite navigation)|Galileo]].<ref>{{cite web|url=https://www.euspa.europa.eu/european-space/galileo/What-Galileo |title=Galileo is the European global satellite-based navigation system |website=www.euspa.europa.eu|date=26 January 2024 |access-date=26 January 2024}}</ref> Two regional systems are operational: India's [[Indian Regional Navigation Satellite System|NavIC]]<ref name=":0" /> and Japan's [[Quasi-Zenith Satellite System|QZSS]].<ref name=":2" />

''[[Satellite-based augmentation system]]s'' (SBAS), designed to enhance the accuracy of GNSS,<ref name=":1">{{cite web |last1=Kriening |first1=Torsten |title=Japan Prepares for GPS Failure with Quasi-Zenith Satellites |url=https://spacewatch.global/2019/01/japan-prepares-for-gps-failure-with-quasi-zenith-satellites/ |website=SpaceWatch.Global |access-date=10 August 2019 |date=23 January 2019}}</ref> include Japan's [[Quasi-Zenith Satellite System]] (QZSS),<ref name=":1">{{cite web |last1=Kriening |first1=Torsten |title=Japan Prepares for GPS Failure with Quasi-Zenith Satellites |url=https://spacewatch.global/2019/01/japan-prepares-for-gps-failure-with-quasi-zenith-satellites/ |website=SpaceWatch.Global |access-date=10 August 2019 |date=23 January 2019}}</ref> India's [[GAGAN]] and the European [[EGNOS]], all of them based on GPS. Previous iterations of the BeiDou navigation system and the present [[Indian Regional Navigation Satellite System]] (IRNSS), operationally known as NavIC, are examples of stand-alone operating '''regional navigation satellite systems''' ('''RNSS''').<ref>{{Cite book |url=https://www.isro.gov.in/sites/default/files/satnav_policy-29.pdf |title=Indian Satellite Navigation Policy - 2021 (Draft) |publisher=Department of Space |year=2021 |location=Bengaluru, India |pages=7 |quote="ISRO/DOS shall work towards expanding the coverage from regional to global to ensure availability of NavIC standalone signal in any part of the world without relying on other GNSS and aid in wide utilisation of Indian navigation system across the globe." |access-date=27 July 2022 |archive-date=30 July 2021 |archive-url=https://web.archive.org/web/20210730141223/https://www.isro.gov.in/sites/default/files/satnav_policy-29.pdf |url-status=dead }}</ref>

[[Satellite navigation device]]s determine their location ([[longitude]], [[latitude]], and [[altitude]]/[[elevation]]) to high precision (within a few centimeters to meters) using [[time signal]]s transmitted along a [[Line-of-sight propagation|line of sight]] by [[radio]] from satellites. The system can be used for providing position, navigation or for tracking the position of something fitted with a receiver (satellite tracking). The signals also allow the electronic receiver to calculate the current local time to a high precision, which allows time synchronisation. These uses are collectively known as '''Positioning, Navigation and Timing''' (PNT). Satnav systems operate independently of any telephonic or internet reception, though these technologies can enhance the usefulness of the positioning information generated.

Global coverage for each system is generally achieved by a [[satellite constellation]] of 18–30 [[medium Earth orbit]] (MEO) satellites spread between several [[orbital planes]]. The actual systems vary, but all use [[orbital inclination]]s of >50° and [[orbital period]]s of roughly twelve hours<!-- no, only some do, as can be seen in the table comparing systems that exists in this article --> (at an altitude of about {{convert|20000|km|mi|disp=or}}).{{citation needed (lead)|date=May 2025}}