Editing Low Earth orbit (section)

{{Short description|Orbit around Earth between 160 and 2000 km}}
[[File:ISS-44 Milky Way.jpg|thumb|upright=1.6|A view from the [[International Space Station]] in a low Earth orbit (LEO) at about {{cvt|400|km|mi|abbr=on}}, with yellow-green [[airglow]] visible at Earth's [[horizon]], where roughly at an altitude of {{cvt|100|km|mi|abbr=on}} the [[Boundary of space|boundary between Earth and outer space]] lies and flying speeds reach [[orbital speed|orbital velocities]].]]

A '''low Earth orbit''' ('''LEO''') is an [[geocentric orbit|orbit around Earth]] with a [[orbital period|period]] of 128 minutes or less (making at least 11.25 orbits per day) and an [[orbital eccentricity|eccentricity]] less than 0.25.<ref>{{cite web |url=https://www.space-track.org/#/recent |title=Current Catalog Files |access-date=July 13, 2018 |quote=LEO: Mean Motion > 11.25 & Eccentricity < 0.25 |archive-date=June 26, 2018 |archive-url=https://web.archive.org/web/20180626190758/https://www.space-track.org/#/recent |url-status=live}}</ref> Most of the artificial objects in [[outer space]] are in LEO, peaking in number at an altitude around {{cvt|800|km|mi|abbr=on}},<ref name="l496">{{cite thesis | last=Muciaccia | first=Andrea | title=Fragmentations in low Earth orbit: event detection and parent body identification | date=2021 | doi=10.13140/RG.2.2.27621.52966 | page=}}</ref> while the farthest in LEO, before [[medium Earth orbit]] (MEO), have an altitude of 2,000 kilometers, about one-third of the [[Earth radius|radius of Earth]] and near the beginning of the [[Van Allen radiation belt#Inner belt|inner Van Allen radiation belt]].

The term ''LEO region'' is used for the area of space below an [[altitude]] of {{cvt|2000|km|mi}} (about one-third of Earth's radius).<ref name="UNOOSA">{{cite web |date=September 2007 |title=IADC Space Debris Mitigation Guidelines |url=http://www.unoosa.org/documents/pdf/spacelaw/sd/IADC-2002-01-IADC-Space_Debris-Guidelines-Revision1.pdf |publisher=INTER-AGENCY SPACE DEBRIS COORDINATION COMMITTEE: Issued by Steering Group and Working Group 4 |quote=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 |access-date=2018-07-17 |archive-date=2018-07-17 |archive-url=https://web.archive.org/web/20180717154257/http://www.unoosa.org/documents/pdf/spacelaw/sd/IADC-2002-01-IADC-Space_Debris-Guidelines-Revision1.pdf |url-status=live}}</ref> Objects in orbits that pass through this zone, even if they have an [[apogee]] further out or are [[sub-orbital spaceflight|sub-orbital]], are carefully tracked since they present a collision risk to the many LEO satellites.

No [[human spaceflight]]s other than the lunar missions of the [[Apollo program]] (1968-1972) have taken place beyond LEO. All [[space station]]s to date have operated [[geocentric orbit|geocentric]] within LEO.