Editing Low Earth orbit (section)

==Orbital characteristics==
The mean orbital velocity needed to maintain a stable low Earth orbit is about {{convert|7.8|km/s|mi/s|sigfig=2|abbr=on}}, which translates to {{convert|28000|km/h|mi/h|sigfig=2|abbr=on}}. However, this depends on the exact altitude of the orbit. Calculated for a circular orbit of {{convert|200|km|abbr=on}} the orbital velocity is {{convert|7.79|km/s|mi/s|sigfig=3|abbr=on}}, but for a higher {{convert|1500|km|abbr=on}} orbit the velocity is reduced to {{convert|7.12|km/s|mi/s|sigfig=3|abbr=on}}.<ref>{{Cite web|url=http://www.spaceacademy.net.au/watch/track/leopars.htm|title=LEO parameters|website=www.spaceacademy.net.au|access-date=2015-06-12|archive-date=2016-02-11|archive-url=https://web.archive.org/web/20160211202014/http://www.spaceacademy.net.au/watch/track/leopars.htm|url-status=live}}</ref> The launch vehicle's [[delta-v]] needed to achieve low Earth orbit starts around {{convert|9.4|km/s|mi/s|sigfig=2|abbr=on}}.

The pull of [[gravity]] in LEO is only slightly less than on the Earth's surface. This is because the distance to LEO from the Earth's surface is much less than the Earth's radius. However, an object in orbit is in a permanent [[free fall]] around Earth, because in orbit the [[Gravity|gravitational force]] and the [[centrifugal force]] balance each other out.{{efn|It is important to note here that “free fall” by definition requires that ''gravity'' is the only force acting on the object. That definition is still fulfilled when falling around Earth, as the other force, the ''centrifugal force'' is a [[fictitious force]].}} As a result, spacecraft in orbit continue to stay in orbit, and people inside or outside such craft continuously experience [[weightlessness]].

Objects in LEO orbit Earth between the denser part of the atmosphere and below the inner [[Van Allen radiation belt]].  They encounter atmospheric drag from [[gases]] in the [[thermosphere]] (approximately 80–600&nbsp;km above the surface) or [[exosphere]] (approximately {{cvt|600|km|-2|disp=or}} and higher), depending on orbit height.  Satellites in orbits that reach altitudes below {{cvt|300|km}} [[Orbital decay|decay]] quickly due to atmospheric drag. 

Equatorial low Earth orbits ('''ELEO''') are a subset of LEO. These orbits, with low [[orbital inclination]], allow rapid revisit times over low-latitude locations on Earth.  [[Retrograde and prograde motion|Prograde]] equatorial LEOs also have lower [[delta-v]] launch requirements because they take advantage of the Earth's rotation. Other useful LEO orbits including [[polar orbit]]s and [[Sun-synchronous orbit]]s have a higher inclinations to the equator and provide coverage for higher latitudes on Earth. Some of the first generation of [[Starlink]] satellites used polar orbits which provide coverage everywhere on Earth.  Later Starlink constellations orbit at a lower inclination and provide more coverage for populated areas.

Higher orbits include [[medium Earth orbit]] (MEO), sometimes called intermediate circular orbit (ICO), and further above, [[geostationary orbit]] (GEO). Orbits higher than low orbit can lead to early failure of electronic components due to intense [[radiation]] and charge accumulation.

In 2017, "[[very low Earth orbit]]s" ('''VLEO''') began to be seen in [[regulatory agency|regulatory]] filings. These orbits, below about {{Cvt|450|km|mi|-1}}, require the use of novel technologies for [[orbit raising]] because they operate in orbits that would ordinarily decay too soon to be economically useful.<ref>{{Cite journal|last1=Crisp|first1=N. H.|last2=Roberts|first2=P. C. E.|last3=Livadiotti|first3=S.|last4=Oiko|first4=V. T. A.|last5=Edmondson|first5=S.|last6=Haigh|first6=S. J.|last7=Huyton|first7=C.|last8=Sinpetru|first8=L.|last9=Smith|first9=K. L.|last10=Worrall|first10=S. D.|last11=Becedas|first11=J.|date=August 2020|title=The Benefits of Very Low Earth Orbit for Earth Observation Missions|journal=[[Progress in Aerospace Sciences]]|volume=117|pages=100619|doi=10.1016/j.paerosci.2020.100619|arxiv=2007.07699|bibcode=2020PrAeS.11700619C|s2cid=220525689}}</ref><ref name=pa20170303>{{cite news |last=Messier |first=Doug |url=http://www.parabolicarc.com/2017/03/03/spacex-launch-12000-satellites/ |title=SpaceX Wants to Launch 12,000 Satellites |work=Parabolic Arc |date=2017-03-03 |access-date=2018-01-22 |archive-date=2020-01-22 |archive-url=https://web.archive.org/web/20200122203256/http://www.parabolicarc.com/2017/03/03/spacex-launch-12000-satellites/ |url-status=live }}</ref>