Medium Earth orbit (MEO)

A host of medium Earth orbits (MEO) exist between LEO and GEO, specifically at altitudes between 1,243 and 22,236 miles (2,000 and 35,786 km), but most typically between 12,552 and 12,831 miles (20,200 and 20,650 km). All objects in MEO feature orbital periods less than 24 hours, which extend down to a minimum of two hours. Medium Earth orbits, currently home to around 140 satellites, are ideal for navigation satellites, which is why Global Positioning System (GPS) satellites are placed there.

There are two main types of MEOs to be aware of, as NASA explains:

The semi-synchronous orbit is a near-circular orbit (low eccentricity) 26,560 kilometers from the center of the Earth (about 20,200 kilometers above the surface). A satellite at this height takes 12 hours to complete an orbit. As the satellite moves, the Earth rotates underneath it. In 24-hours, the satellite crosses over the same two spots on the equator every day. This orbit is consistent and highly predictable. It is the orbit used by the Global Positioning System (GPS) satellites.

The second common medium Earth orbit is the Molniya orbit. Invented by the Russians, the Molniya orbit works well for observing high latitudes. A geostationary orbit is valuable for the constant view it provides, but satellites in a geostationary orbit are parked over the equator, so they don’t work well for far northern or southern locations, which are always on the edge of view for a geostationary satellite. The Molniya orbit offers a useful alternative.

MEO is useful in the same way that LEO is useful, in that objects don’t need to take specific routes around Earth, allowing for an assortment of applications.