Medium Earth orbit (MEO) lies between low Earth orbit and geostationary orbit. It is far less crowded than low Earth orbit, but it hosts some of the most important satellite systems in the world. This article looks at the main constellations in MEO and how many satellites they use, based on figures published by their operators.
The main MEO systems
- GPS (United States): according to the US government's GPS website, the US Space Force has been flying 31 operational GPS satellites for well over a decade. They orbit at approximately 20,200 km in six orbital planes and circle the Earth twice a day.
- Galileo (Europe): according to ESA, the fully operational system will have 24 satellites plus spares in MEO at an altitude of 23,222 km, with eight active satellites in each of three orbital planes.
- O3b mPOWER (SES): a communications system in MEO about 8,000 km above the Earth. SES refers to 13 O3b mPOWER satellites in total.
Is there an official total?
We have not found an official, current count of all satellites in MEO from a primary source. The numbers above therefore describe individual systems, not the whole orbit.
Why so few compared with LEO?
A satellite in MEO sees a much larger part of the Earth than one in LEO, so fewer satellites are needed for global coverage. Navigation systems need only a few dozen satellites, while broadband constellations in LEO use thousands. Our article on LEO, MEO and GEO compares the orbits in detail.
Frequently asked questions
How many GPS satellites are there?
According to GPS.gov, the US Space Force has been flying 31 operational GPS satellites.
How many satellites does Galileo have?
According to ESA, the fully operational system will have 24 satellites plus spares in MEO.
What altitude is MEO?
Between LEO and GEO. GPS flies at about 20,200 km, Galileo at 23,222 km and O3b mPOWER at about 8,000 km.
Related reading
- LEO, MEO and GEO Satellites Compared
- Satellite Constellations Explained
- The Most Important Satellite Orbits Explained
Sources
Cover image: Sunset over the Indian Ocean photographed from the International Space Station, May 2010. Credit: NASA (iss023e057948), public domain.