Low Earth orbit

A view from the International Space Station, in a low Earth orbit (LEO) at about 400 km (250 mi), with yellow-green airglow visible at Earth's horizon, where roughly at an altitude of 100 km (62 mi) the boundary between Earth and outer space lies and flying speeds reach orbital velocities

A low Earth orbit (LEO) is an orbit around Earth with a period of 128 minutes or less (making at least 11.25 orbits per day) and an eccentricity less than 0.25. Most of the artificial objects in outer space are in LEO, peaking in number at an altitude around 800 km (500 mi), while the farthest in LEO, before medium Earth orbit (MEO), have an altitude of 2,000 kilometers, about one-third of the radius of Earth and near the beginning of the inner Van Allen radiation belt.

The term LEO region is used for the area of space below an altitude of 2,000 km (1,200 mi) (about one-third of Earth's radius). Objects in orbits that pass through this zone, even if they have an apogee further out or are sub-orbital, are carefully tracked since they present a collision risk to the many LEO satellites.

The only human spaceflights beyond LEO were the nine lunar missions of the Apollo program from 1968 to 1972 and the Artemis II lunar flyby in 2026. All space stations as of 2026 have operated in geocentric orbits within LEO.

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