Amedium Earth orbit (MEO) is anEarth-centered orbit with an altitude above alow Earth orbit (LEO) and below ahigh Earth orbit (HEO) – between 2,000 and 35,786 km (1,243 and 22,236 mi) above sea level.[1]
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 ageosynchronous 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 anorbital period of less than 24 hours, with the minimum period (for a circular orbit at the lowest MEO altitude) about 2 hours.[2]
Satellites in MEO orbits are perturbed by solar radiation pressure, which is the dominating non-gravitational perturbing force.[3] 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 theVan Allen radiation belts, which can damage satellites’ electronic systems without special shielding.[4]
A medium Earth orbit is sometimes calledmid Earth orbit[1] orintermediate circular orbit (ICO).[2]
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Two medium Earth orbits are particularly significant. A satellite in thesemi-synchronous orbit at an altitude of approximately 20,200 kilometres (12,600 mi) has an orbital period of 12 hours and passes over the same two spots on the equator every day.[1] This reliably predictable orbit is used by theGlobal Positioning System (GPS)constellation.[2] Other navigation satellite systems use similar medium Earth orbits includingGLONASS (with an altitude of 19,100 kilometres, 11,900 mi),[5]Galileo (with an altitude of 23,222 kilometres, 14,429 mi)[6] andBeiDou (with an altitude of 21,528 kilometres, 13,377 mi).[7]
TheMolniya orbit has a highinclination of 63.4° and higheccentricity 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 AmericanSirius Satellite Radio andXM Satellite Radio satellites and the RussianMolniya military communications satellites, after which it is named.[1]
Communications satellites in MEO include theO3b andO3b mPOWER constellations for low-latencybroadband anddata backhaul to maritime, aero and remote locations (with an altitude of 8,063 kilometres, 5,010 mi).[8]
Communications satellites to cover the North and South Pole are also put in MEO.[9]
Telstar 1, an experimental communications satellite launched in 1962, orbited in MEO.[10]
In May 2022,Kazakhstani mobile network operator,Kcell, and satellite owner and operator,SES used SES'sO3b MEOsatellite 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 alatency (delay) five times lower than on the existing platform based ongeostationary orbit satellites.[11][12]
In September 2023, satellite operatorSES announced the first satellite internet service to usesatellite constellations in both MEO andLow Earth Orbit (LEO). The SES Cruise mPOWERED + Starlink service will use SES'sO3b mPOWER MEO satellites andSpaceX'sStarlink 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 thatVirgin Voyages will be the first cruise line to deploy the service.[13][14][15]
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, wheregeostationary satellites are and where after their end of use they are parked in similar orbits, so-calledgraveyard orbits.
