Editing Low Earth orbit (section)

== Defining characteristics ==
A wide variety of sources<ref>{{Cite web|title=Definition of LOW EARTH ORBIT|url=https://www.merriam-webster.com/dictionary/low%20earth%20orbit|access-date=2018-07-08|website=Merriam-Webster Dictionary|language=en|archive-date=2018-07-08|archive-url=https://web.archive.org/web/20180708162215/https://www.merriam-webster.com/dictionary/low%20earth%20orbit|url-status=live}}</ref><ref>{{Cite web|title=Frequently Asked Questions|url=https://www.faa.gov/space/additional_information/faq/#s1|access-date=2020-02-14|publisher=FAA|language=en-us|quote=LEO refers to orbits that are typically less than 2,400 km (1,491 mi) in altitude.|archive-date=2020-06-02|archive-url=https://web.archive.org/web/20200602021356/https://www.faa.gov/space/additional_information/faq/#s1|url-status=live}}</ref><ref>{{Cite news|last=Campbell|first=Ashley|date=2015-07-10|title=SCaN Glossary|language=en|publisher=NASA|url=https://www.nasa.gov/directorates/heo/scan/definitions/glossary/index.html#L|access-date=2018-07-12|quote=Low Earth Orbit (LEO): A geocentric orbit with an altitude much less than the Earth's radius. Satellites in this orbit are between 80 and 2000 kilometers above the Earth's surface.|archive-date=2020-08-03|archive-url=https://web.archive.org/web/20200803122937/https://www.nasa.gov/directorates/heo/scan/definitions/glossary/index.html#L|url-status=live}}</ref> define LEO in terms of [[altitude]]. The altitude of an object in an [[elliptic orbit]] can vary significantly along the orbit. Even for [[circular orbit]]s, the altitude above ground can vary by as much as {{cvt|30|km|mi}} (especially for [[polar orbit]]s) due to the [[flattening|oblateness]] of [[figure of the Earth|Earth's spheroid figure]] and local [[topography]].  While definitions based on altitude are inherently ambiguous, most of them fall within the range specified by an orbit period of 128 minutes because, according to [[orbital period|Kepler's third law]], this corresponds to a [[semi-major and semi-minor axes|semi-major axis]] of {{cvt|8413|km|mi}}. For circular orbits, this in turn corresponds to an altitude of {{cvt|2042|km|mi}} above the mean radius of Earth, which is consistent with some of the upper altitude limits in some LEO definitions.

The LEO region is defined by some sources as a region in space that LEO orbits occupy.<ref name="UNOOSA" /><ref>{{Cite news|others=David Hitt : NASA Educational Technology Services, Alice Wesson : JPL, J.D. Harrington : HQ;, Larry Cooper : HQ;, Flint Wild : MSFC;, Ann Marie Trotta : HQ;, Diedra Williams : MSFC|date=2015-06-01|title=What Is an Orbit?|language=en|work=NASA|url=https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-orbit-58.html|access-date=2018-07-08|quote=LEO is the first 100 to 200 miles (161 to 322&nbsp;km) of space.|archive-date=2018-03-27|archive-url=https://web.archive.org/web/20180327095840/https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-orbit-58.html|url-status=live}}</ref><ref>{{Cite news|last=Steele|first=Dylan|date=2016-05-03|title=A Researcher's Guide to: Space Environmental Effects|language=en|page=7|work=NASA|url=https://www.nasa.gov/connect/ebooks/researchers_guide_space_environment_detail.html|access-date=2018-07-12|quote=the low-Earth orbit (LEO) environment, defined as 200–1,000 km above Earth's surface|archive-date=2016-11-17|archive-url=https://web.archive.org/web/20161117060640/http://www.nasa.gov/connect/ebooks/researchers_guide_space_environment_detail.html|url-status=live}}</ref> Some [[highly elliptical orbit]]s may pass through the LEO region near their lowest altitude (or [[apsis|perigee]]) but are not in a LEO orbit because their highest altitude (or [[apsis|apogee]]) exceeds {{cvt|2000|km|mi|0}}. [[sub-orbital spaceflight|Sub-orbital]] objects can also reach the LEO region but are not in a LEO orbit because they [[atmospheric entry|re-enter the atmosphere]]. The distinction between LEO orbits and the LEO region is especially important for analysis of possible collisions between objects which may not themselves be in LEO but could collide with satellites or debris in LEO orbits.

[[File:Orbitalaltitudes.svg|center|700px]]