Medium Earth orbit
{{short description|Earth-centered orbit above low Earth orbit and below geostationary orbit}}
{{Comparison satellite navigation orbits}}
File:Orbits schematic edit.png and the distance of the orbit of the Moon for reference and to scale.]]
A medium Earth orbit (MEO) is an Earth-centered orbit with an altitude above a low Earth orbit (LEO) and below a high Earth orbit (HEO) – between {{convert|2000|and|35786|km|mi|0|abbr=on}} above sea level.[https://earthobservatory.nasa.gov/features/OrbitsCatalog/page1.php Catalog of Earth Satellite Orbits]. NASA Earth Observatory. 4 September 2009. Accessed 2 May 2021.
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 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 hours, with the minimum period (for a circular orbit at the lowest MEO altitude) about 2 hours.{{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 }}
Satellites in MEO orbits are perturbed by solar radiation pressure, which is the dominating non-gravitational perturbing force.{{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 }} Other perturbing forces include: 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 belts, which can damage satellites’ electronic systems without special shielding.[https://aerospace.csis.org/aerospace101/popular-orbits-101/ "Popular Orbits 101"]. Aerospace Security. 26 October 2020. Accessed 2 May 2021.
A medium Earth orbit is sometimes called mid Earth orbit or intermediate circular orbit (ICO).
Applications
File:Apollo 17 Blue Marble original orientation (AS17-148-22727).jpg 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 hours and passes over the same two spots on the equator every day. This reliably predictable orbit is used by the Global Positioning System (GPS) constellation. Other navigation satellite systems use similar medium Earth orbits including GLONASS (with an altitude of {{convert|19100|km|disp=comma}}),{{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}} Galileo (with an altitude of {{convert|23222|km|mi|0|disp=comma}})[http://www.esa.int/Our_Activities/Navigation/Galileo/Galileo_satellites Galileo Satellites]. and BeiDou (with an altitude of {{convert|21528|km|mi|0|disp=comma}}).[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.
The Molniya orbit has a high inclination of 63.4° and high eccentricity of 0.722 with a period of 12 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 military communications satellites, after which it is named.
Communications satellites in MEO include the O3b and O3b mPOWER constellations for low-latency broadband and data backhaul to maritime, aero and remote locations (with an altitude of {{convert|8063|km|mi|0|disp=comma}}).[https://www.ses.com/networks/networks-and-platforms/o3b-meo O3b satellites]
Communications satellites to cover the North and South Pole are also put in MEO.[http://exnetapps.intelsat.com/resources/satellite-basics/benefits.asp Satellite Basics: Solution Benefits]. {{webarchive|url=https://archive.today/20131119183307/http://exnetapps.intelsat.com/resources/satellite-basics/benefits.asp |date=2013-11-19 }}.
Telstar 1, an experimental communications satellite launched in 1962, orbited in MEO.{{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 }}
In May 2022, Kazakhstani mobile network operator, Kcell, and satellite owner and operator, 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 (delay) five times lower than on the existing platform based on geostationary orbit satellites.[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{{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}}
In September 2023, satellite operator SES announced the first satellite internet service to use satellite constellations in both MEO and 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 announced that Virgin Voyages will be the first cruise line to deploy the service.[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{{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}}[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
Space debris
File:Space sustainability urgency in earth orbits white.png
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 satellites are and where after their end of use they are parked in similar orbits, so-called graveyard orbits.
See also
Explanatory notes
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References
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{{Orbits}}
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