View source for Medium Earth orbit

{{short description|Earth-centered orbit above low Earth orbit and below geostationary orbit}}
{{Comparison satellite navigation orbits}}
[[File:Orbitalaltitudes.jpg|upright=1.2|thumb|To-scale diagram of low, medium, and [[high Earth orbit]]s]]
[[File:Orbits schematic edit.png|upright=1.2|thumb|Space of Medium Earth orbits (MEO) as pink area, with [[Earth]] and the [[Lunar distance|distance of the orbit of the Moon]] for reference and to scale.]]
A '''medium Earth orbit''' ('''MEO''') is an [[geocentric orbit|Earth-centered orbit]] with an altitude above a [[low Earth orbit]] (LEO) and below a [[high Earth orbit]] (HEO)&nbsp;– between {{convert|2000|and|35786|km|mi|0|abbr=on}} above sea level.<ref name="NASA_EO">[https://earthobservatory.nasa.gov/features/OrbitsCatalog/page1.php ''Catalog of Earth Satellite Orbits'']. NASA Earth Observatory. 4 September 2009. Accessed 2 May 2021.</ref>

The boundary between MEO and LEO is an arbitrary altitude chosen by accepted convention, whereas the boundary between MEO and HEO is the particular altitude of a [[geosynchronous orbit]], in which a satellite takes 24&nbsp;hours to circle the Earth, the same period as the Earth’s own rotation. All satellites in MEO have an [[orbital period]] of less than 24&nbsp;hours, with the minimum period (for a circular orbit at the lowest MEO altitude) about 2&nbsp;hours.<ref name=nasa20120718>{{cite web |title=Definitions of geocentric orbits from the Goddard Space Flight Center |url=http://gcmd.nasa.gov/User/suppguide/platforms/orbit.html |work=User support guide: platforms  |publisher=NASA Goddard Space Flight Center |access-date=8 July 2012 |url-status=dead |archive-url=https://web.archive.org/web/20100527132541/http://gcmd.nasa.gov/User/suppguide/platforms/orbit.html |archive-date=27 May 2010 }}</ref>

Satellites in MEO orbits are perturbed by solar radiation pressure, which is the dominating non-gravitational perturbing force.<ref>{{cite journal |last1=Bury |first1=Grzegorz |last2=Sośnica |first2=Krzysztof |last3=Zajdel |first3=Radosław |last4=Strugarek |first4=Dariusz |title=Toward the 1-cm Galileo orbits: challenges in modeling of perturbing forces |journal=Journal of Geodesy |date=February 2020 |volume=94 |issue=2 |pages=16 |doi=10.1007/s00190-020-01342-2|bibcode=2020JGeod..94...16B |doi-access=free }}</ref> Other perturbing forces include: [[Albedo#Terrestrial albedo|Earth's albedo]], navigation antenna thrust, and thermal effects related to heat re-radiation.

The MEO region includes the two zones of energetic charged particles above the equator known as the [[Van Allen radiation belt]]s, which can damage satellites’ electronic systems without special shielding.<ref>[https://aerospace.csis.org/aerospace101/popular-orbits-101/ "Popular Orbits 101"]. Aerospace Security. 26 October 2020. Accessed 2 May 2021.</ref>

A medium Earth orbit is sometimes called '''mid Earth orbit'''<ref name="NASA_EO"/> or '''intermediate circular orbit''' ('''ICO''').<ref name=nasa20120718/>

== Applications ==
[[File:Apollo 17 Blue Marble original orientation (AS17-148-22727).jpg|thumb|right|A [[Hasselblad|camera]] photo of Earth from a distance of {{convert|29400|km|mi|sp=us|abbr=off}}, a distance of higher medium Earth orbits (uncropped and unrotated ''[[The Blue Marble]]'' image, from [[Apollo 17]] during lunar transfer).]]
Two medium Earth orbits are particularly significant. A satellite in the ''[[semi-synchronous orbit]]'' at an altitude of approximately {{convert|20200|km}} has an orbital period of 12&nbsp;hours and passes over the same two spots on the equator every day.<ref name="NASA_EO"/> This reliably predictable orbit is used by the [[Global Positioning System]] (GPS) [[satellite constellation|constellation]].<ref name=nasa20120718/> Other navigation satellite systems use similar medium Earth orbits including [[GLONASS]] (with an altitude of {{convert|19100|km|disp=comma}}),<ref>{{cite web |url=http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA484380 |archive-url=https://web.archive.org/web/20110629000017/http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA484380 |url-status=dead |archive-date=June 29, 2011 |title=The Global Navigation System GLONASS: Development and Usage in the 21st Century |publisher=34th Annual Precise Time and Time Interval (PTTI) Meeting |year=2002 |access-date=28 February 2019}}</ref> [[Galileo positioning system|Galileo]] (with an altitude of {{convert|23222|km|mi|0|disp=comma}})<ref>[http://www.esa.int/Our_Activities/Navigation/Galileo/Galileo_satellites Galileo Satellites].</ref> and [[BeiDou]] (with an altitude of {{convert|21528|km|mi|0|disp=comma}}).<ref>[http://www2.unb.ca/gge/Resources/beidou_icd_english_ver2.0.pdf ''BeiDou Navigation Satellite System Signal In Space'']. China Satellite Navigation Office. December 2013. Access 2 May 2021.</ref>

The ''[[Molniya orbit]]'' has a high [[orbital inclination|inclination]] of 63.4° and high [[orbital eccentricity|eccentricity]] of 0.722 with a period of 12&nbsp;hours, so a satellite spends most of its orbit above the chosen area in high latitudes. This orbit was used by the (now defunct) North American [[Sirius Satellite Radio]] and [[XM Satellite Radio]] satellites and the Russian [[Molniya (satellite)|Molniya]] military communications satellites, after which it is named.<ref name="NASA_EO"/>

Communications satellites in MEO include the [[O3b]] and [[O3b mPOWER]] constellations for low-[[Latency (engineering)|latency]] [[Satellite Internet access|broadband]] and [[Backhaul (telecommunications)|data backhaul]] to maritime, aero and remote locations (with an altitude of {{convert|8063|km|mi|0|disp=comma}}).<ref>[https://www.ses.com/networks/networks-and-platforms/o3b-meo O3b satellites]</ref>

Communications satellites to cover the North and South Pole are also put in MEO.<ref>[http://exnetapps.intelsat.com/resources/satellite-basics/benefits.asp Satellite Basics: Solution Benefits<!-- Bot generated title -->]. {{webarchive|url=https://archive.today/20131119183307/http://exnetapps.intelsat.com/resources/satellite-basics/benefits.asp |date=2013-11-19 }}.</ref>

[[Telstar]] 1, an experimental communications satellite launched in 1962, orbited in MEO.<ref>{{Cite web |url=http://iml.jou.ufl.edu/projects/Fall99/Coffey/MEO.HTM |title=Medium Earth Orbit |website=Internet in the Sky |access-date=2007-01-04 |archive-url=https://web.archive.org/web/20170609231841/http://iml.jou.ufl.edu/projects/Fall99/Coffey/MEO.HTM |archive-date=2017-06-09 |url-status=dead }}</ref>

In May 2022, [[Kazakhstan|Kazakhstani]] mobile network operator, [[Kcell]], and satellite owner and operator, [[SES (company)|SES]] used SES's [[O3b]] MEO [[satellite constellation]] to demonstrate that MEO satellites could be used to provide high-speed mobile internet to remote regions of Kazakhstan for reliable video calling, conferencing and streaming, and web browsing, with a [[latency (engineering)|latency (delay)]] five times lower than on the existing platform based on [[geostationary orbit]] satellites.<ref>[https://www.commsupdate.com/articles/2022/05/26/kcell-ses-demo-o3b-satellite-enabled-remote-mobile-services/ ''Kcell, SES demo O3b satellite-enabled remote mobile services''] Comms Update. 26 May 2022. Accessed 30 May 2022</ref><ref>{{cite press release|publisher=SES|date=25 May 2022 |url=https://www.ses.com/press-release/kcell-and-ses-successfully-demonstrate-cellular-network-connectivity-kazakhstan|title=Kcell and SES Successfully Demonstrate Cellular Network connectivity in Kazakhstan|access-date=30 May 2022}}</ref>

In September 2023, satellite operator [[SES (company)|SES]] announced the first satellite internet service to use [[satellite constellation]]s in both MEO and [[Low Earth Orbit|Low Earth Orbit (LEO)]]. The SES Cruise mPOWERED + Starlink service will use SES's [[O3b mPOWER]] MEO satellites and [[SpaceX]]'s [[Starlink]] LEO system to provide cruise ship passengers with internet, social media and video calls at up to 3 Gbps per ship anywhere in the World. Subsequently, in February 2024, [[SES (company)|SES]] announced that [[Virgin Voyages]] will be the first cruise line to deploy the service.<ref>[https://www.satellitetoday.com/mobility/2023/09/13/ses-teams-up-with-starlink-to-package-connectivity-for-the-cruise-segment/ ''SES Teams Up with Starlink to Package Connectivity for the Cruise Segment''] Via Satellite. 13 September 2023. Accessed 27 February 2024</ref><ref>{{cite press release|publisher=SES|date=13 September 2023 |url=https://www.ses.com/press-release/ses-introduces-cruise-industrys-first-integrated-meo-leo-service-starlink|title=SES Introduces Cruise Industry’s First Integrated MEO-LEO Service with Starlink|access-date=27 February 2024}}</ref><ref>[https://cruiseindustrynews.com/cruise-news/2024/02/virgin-voyages-rolls-out-new-improved-internet-package-with-ses/ ''Virgin Voyages Rolls Out New Improved Internet Package with SES''] Cruise Industry News. 26 February 2024. Accessed 27 February 2024</ref>

==Space debris==
[[File:Space sustainability urgency in earth orbits white.png|thumb|upright=2|Infographic showing the space debris situation extending from low Earth orbit, across medium Earth orbits, until the lowest high Earth orbits.]]

[[Space debris]] in medium Earth orbit stays practically permanently   orbiting Earth. Most space debris extends to the lowest high Earth orbits just beyond the edge of medium Earth orbit, where [[geostationary satellite]]s are and where after their end of use they are parked in similar orbits, so-called [[graveyard orbit]]s.

==See also==
{{cmn|
* [[Atmospheric reentry]]
* [[Escape velocity]]
* [[Geostationary orbit|Geostationary Earth orbit]] (GEO)
* [[High Earth orbit]] (HEO)
* [[Highly elliptical orbit]] (HEO)
* [[Graveyard orbit]]
* [[International Space Station]]
* [[List of orbits]]
* [[Low Earth orbit]] (LEO)
* [[Satellite phone]]
* [[Suborbital spaceflight]]
* [[Geocentric_orbit#Geocentric_orbit_types|Types of geocentric orbit]]
}}

== Explanatory notes ==
{{reflist|group=lower-alpha}}

==References==
{{Reflist}}

{{Orbits}}
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[[Category:Earth orbits]]