Medium Earth Orbit (meo)

What Is Medium Earth Orbit (MEO)?

Medium Earth Orbit (MEO) is a class of Earth orbit occupying the altitude band from approximately 2,000 to 35,786 kilometers above the Earth's surface, positioned between the lower boundary of Low Earth Orbit (LEO) and the altitude of Geostationary Earth Orbit (GEO). Satellites operating in MEO complete one to several full orbits per day depending on their altitude, which distinguishes them from geostationary satellites that remain fixed relative to the Earth's surface. MEO is used most prominently by the satellite constellations that provide Global Navigation Satellite System (GNSS) services, and is increasingly being considered for broadband communication networks requiring lower signal latency than GEO.

The region is bounded below by the outer edge of the densest portion of the Van Allen radiation belts, which impose design constraints on satellite electronics and solar panel materials. Orbit selection within MEO balances coverage geometry, signal propagation delay, launch cost, and radiation tolerance.

Orbital Characteristics

MEO satellites at typical GNSS altitudes of approximately 19,000 to 24,000 km have orbital periods of roughly 11 to 14 hours. At these altitudes, a single satellite has a ground footprint large enough to serve many ground stations simultaneously, but the satellite moves across the sky fast enough that a fixed ground station must switch between satellites as the constellation rotates. This geometry drives the design of satellite constellations toward multiple orbital planes with evenly distributed satellites, so that a minimum number of satellites are always visible above a defined elevation angle at any point on Earth.

NASA's report on medium earth orbits documents the radiation environment and orbital mechanics considerations that shape MEO satellite design, particularly the challenge of operating electronics in the particle flux of the radiation belts.

The principal occupants of MEO are the four major GNSS constellations. The United States GPS constellation operates 24 to 31 satellites at an altitude of approximately 20,200 km in six orbital planes, with each satellite completing two orbits per day. Russia's GLONASS system, the European Union's Galileo, and China's BeiDou also operate their primary navigation satellites in MEO. These constellations collectively support positioning, navigation, and timing services used by civilian and military receivers worldwide.

NASA Earthdata's Global Navigation Satellite System documentation describes how MEO-based GNSS constellations provide the ranging signals that ground receivers use to compute three-dimensional position through trilateration from at least four visible satellites. The orbital altitude of roughly 20,000 km was chosen to provide sufficient coverage with a modest number of satellites while keeping signal travel time to ground receivers manageable.

Communications and Scientific Applications

Beyond navigation, MEO is used by communication satellite operators seeking a middle ground between GEO's 270-millisecond one-way signal delay and LEO's demand for large numbers of satellites to maintain continuous coverage. The European Space Agency's overview of orbital regimes identifies MEO as the orbit used by medium-altitude broadband constellations targeting data latency in the range of 50 to 150 milliseconds, which is acceptable for many real-time applications.

Scientific satellites studying the Van Allen radiation belts and Earth's magnetosphere also operate in MEO, as this altitude places instruments directly within the region of interest.

Applications

Medium Earth Orbit has applications in a wide range of disciplines, including:

  • Global navigation and positioning services via GPS, Galileo, GLONASS, and BeiDou constellations
  • Precision agriculture, using GNSS signals for centimeter-accurate field guidance systems
  • Aviation navigation and instrument approach procedures dependent on GNSS integrity
  • Maritime navigation, where satellite timing underpins chart plotting and traffic separation
  • Scientific study of Earth's radiation environment and magnetospheric dynamics