Medium Earth Orbit (MEO)

Medium Earth Orbit, or MEO, is the wide band of space that sits above Low Earth Orbit and below the ring where satellites appear to hover over one spot. It is the home of the navigation satellites that help your phone know exactly where you are.

Quick facts

• Altitude: roughly 2,000 to 35,786 km above Earth (most navigation satellites fly near ~20,000 km).
• Orbital period (time for one lap): about 2 hours up to just under 24 hours; GPS satellites take about 12 hours.
• Speed: around 3.9 km/s at the GPS altitude of about 20,200 km.
• Inclination (tilt of the orbit): depends on the mission — GPS uses 55 degrees, while the O3b broadband satellites fly near 0 degrees, right over the equator.
• Boundaries: the lower edge (with LEO) is set by convention; the upper edge is the geosynchronous altitude, where one lap takes exactly one sidereal day (the time Earth takes to spin once relative to the stars, about 23 hours 56 minutes).

How it works

A satellite stays up by balancing its forward speed against Earth’s gravity. It is constantly falling toward the planet, but it is also moving sideways so fast that it keeps missing — tracing a closed loop instead of crashing down. Think of throwing a ball so hard that the ground curves away beneath it as fast as it drops.

Higher orbits feel weaker gravity, so a satellite there travels more slowly and each lap takes longer. Near 20,000 km, one lap takes about 12 hours at roughly 3.9 km/s. Because MEO craft sit so much higher than Low Earth Orbit satellites, each one sees a far larger slice of the planet. That is why a modest fleet — for example, 24 GPS satellites spread across six orbital planes tilted at 55 degrees — can keep several satellites above the horizon everywhere at once, which is exactly what a receiver needs to pinpoint a position. A 12-hour orbit also retraces the same ground path each day. This high up, air resistance is negligible; the main nudge on these satellites comes from the pressure of sunlight itself.

Why it’s used

MEO is the sweet spot for global navigation. From about 20,000 km a single satellite covers a huge footprint, so a small constellation can give continuous worldwide coverage with the geometric spread needed to fix a 3D position. That is why every major global navigation system — GPS, GLONASS, Galileo, and BeiDou — lives here.

The lower edge of MEO is also used for fast internet. SES’s O3b and O3b mPOWER satellites ring the planet at about 8,000 km and deliver fiber-like round-trip delay of roughly 140 to 150 milliseconds — far quicker than a satellite parked in the much higher geostationary belt (the ring about 35,786 km up where a satellite appears to hover over one spot) — while still covering wide areas with relatively few craft. MEO also supports some Earth-measuring and space-weather science. In short, it is chosen whenever you want broad, lasting coverage from a manageable number of satellites, without the long signal delay of the geostationary belt or the enormous fleets that Low Earth Orbit requires.

Notable missions

• GPS (NAVSTAR): the U.S. navigation constellation at about 20,200 km, 55-degree inclination, six orbital planes, 12-hour period — the classic MEO system.
• Galileo: the European Union’s global navigation system at about 23,222 km; ESA points to it as the flagship example of MEO, serving everything from aviation to smartphones.
• GLONASS: Russia’s navigation constellation at about 19,100 km.
• BeiDou (MEO segment): China’s navigation satellites at about 21,528 km (BeiDou also uses other orbit types).
• O3b / O3b mPOWER (SES): a near-equatorial broadband constellation at about 8,063 km delivering low-latency connectivity to maritime, enterprise, aviation, and government users; the mPOWER fleet, built by Boeing, began service in 2024.

MEO trades a few real challenges — more radiation near the Van Allen belts, satellites that move across the sky rather than staying fixed, and longer signal delay than Low Earth Orbit — for a powerful payoff: global reach from a small fleet, with far less delay than the geostationary belt. That balance is why it quietly powers the navigation we lean on every day.