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.[1] Most of the artificial objects in outer space are in LEO, peaking in number at an altitude around 800 km (500 mi),[2] 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).[3] 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.

No human spaceflights other than the lunar missions of the Apollo program (1968-1972) and the 2024 Polaris Dawn have taken place beyond LEO. All space stations to date have operated geocentric within LEO.

  1. ^ "Current Catalog Files". Archived from the original on 26 June 2018. Retrieved 13 July 2018. LEO: Mean Motion > 11.25 & Eccentricity < 0.25
  2. ^ Muciaccia, Andrea (2021). Fragmentations in low Earth orbit: event detection and parent body identification (Thesis). doi:10.13140/RG.2.2.27621.52966.
  3. ^ "IADC Space Debris Mitigation Guidelines" (PDF). INTER-AGENCY SPACE DEBRIS COORDINATION COMMITTEE: Issued by Steering Group and Working Group 4. September 2007. Archived (PDF) from the original on 17 July 2018. Retrieved 17 July 2018. Region A, Low Earth Orbit (or LEO) Region – spherical region that extends from the Earth's surface up to an altitude (Z) of 2,000 km