Lagrange point colonization: Difference between revisions

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{{shortShort description|colonizationColonization of five equilibrium points in the orbit of planets or moons}}

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{{Space colonization}}

'''Lagrange point colonization''' is the colonization of the five equilibrium points in the orbit of a planet or its primary moon, called [[Lagrange point]]s. The most obvious such points for colonization are those in the [https://www.facts-guru.info/2020/11/about-earthfacts-about-earth.html Earth]–[https://www.facts-guru.info/2020/11/the-moon-about-moon-moon-is-earths-only.html Moon] and in the Sun–[https://www.facts-guru.info/2020/11/about-earthfacts-about-earth.html Earth] systems. Although it would generally take days or weeks to reach the latter with current technology, it would be possible to generate energy from sunlight at them nearly continuously since they would, due to their considerable distance from [https://www.facts-guru.info/2020/11/about-earthfacts-about-earth.html '''Earth'''], be shaded from the [https://www.facts-guru.info/2020/11/sun-sun-sun-sun-is-star-at-center-of.html Sun] only seldom and then only shortly.

==Earth–Moon==

[[Image:Lagrange points Earth vs Moon.jpg|thumb|right|300px|A diagram showing the five [[Lagrange point]]s in a two-body system, with one body far more massive than the other (e.g. Earth and Moon). In this system {{L3}}–{{L5}} will appear to share the secondary's orbit, although they are situated slightly outside it.]]

The only two stable Lagrange points are {{L4}} and {{L5}}. Lagrange points are stable if the mass of the larger body is at least 25 times the mass of the secondary body.<ref>{{cite web|last1=Fitzpatrick|first1=Richard|title=Stability of Lagrange Points|url=http://farside.ph.utexas.edu/teaching/336k/Newtonhtml/node126.html|website=Newtonian Dynamics|publisher=University of Texas}}</ref><ref>{{cite web|last1=Greenspan|first1=Thomas|title=Stability of the Lagrange Points, L4 and L5|url=http://www.math.cornell.edu/~templier/junior/final_paper/Thomas_Greenspan-Stability_of_Lagrange_points.pdf|date=January 7, 2014}}</ref>. The Earth is over 81 times the mass of the Moon.<ref name = "Pitjeva">{{cite journal|last1=Pitjeva|first1=E.V.|last2=Standish|first2=E.M.|title=Proposals for the masses of the three largest asteroids, the Moon-Earth mass ratio and the Astronomical Unit|journal=Celestial Mechanics and Dynamical Astronomy|date=2009-04-01|volume=103|issue=4|pages=365–372|doi=10.1007/s10569-009-9203-8|bibcode = 2009CeMDA.103..365P |url=https://zenodo.org/record/1000691}}</ref> The [[L5 Society]] was founded to promote settlement by building space stations at these points in the Earth Moon system.

'''Lagrange point colonization''' is a proposed form of [[Space_colonization#Near-Earth space|space colonization]]<ref>{{Cite web|url=https://www.forbes.com/sites/brucedorminey/2012/07/31/death-of-a-sci-fi-dream-free-floating-space-colonies-hit-economic-reality/#3f0895e77431|title=Death Of A Sci-Fi Dream: Free-Floating Space Colonies Hit Economic Reality|last=Dorminey|first=Bruce|author-link=Bruce Dorminey|date=July 31, 2012|website=Forbes|access-date=December 17, 2018}}</ref> of the five equilibrium points in the orbit of a planet or its primary moon, called [[Lagrange point]]s.

An {{L1}} station would have a number of important functions due to its stationary position between the [[Earth]] and [[Moon]]. It is in an excellent ___location to monitor and coordinate communications among various missions on the nearside of the Moon. A vessel launched from L1 could reach any place on the Moon within a few hours to a day. This would make it ideal for crisis management if an emergency occurred on the Moon. Furthermore, it could serve as a way station, especially once built up, and would probably be used to handle tourists and casual visitors to the Moon. A station like this could also serve as a repair center for ships moving throughout the [[Solar System]].

The only two stable Lagrange points are {{L4}} and {{L5}}. Lagrange points are stable if the mass of the larger body is at least 25 times the mass of the secondary body.<ref>{{cite web|last1=Fitzpatrick|first1=Richard|title=Stability of Lagrange Points|url=http://farside.ph.utexas.edu/teaching/336k/Newtonhtml/node126.html|website=Newtonian Dynamics|publisher=University of Texas}}</ref><ref>{{cite web|last1=Greenspan|first1=Thomas|title=Stability of the Lagrange Points, L4 and L5|url=httphttps://www.math.cornell.edu/~templier/junior/final_paper/Thomas_Greenspan-Stability_of_Lagrange_points.pdf|date=January 7, 2014}}</ref>. TheThus, Earththe ispoints overL₄ 81and timesL₅ in the massEarth–Moon ofsystem thehave been proposed as possible sites for space Mooncolonies.<ref name = "Pitjevao'neill">{{cite journal |last1=PitjevaO'Neill |first1=E.VGerard K. |last2author1-link=Standish|first2=E.MGerard K. O'Neill |title=ProposalsThe for the massescolonization of the three largest asteroids, the Moon-Earth mass ratio and the Astronomicalspace Unit|journal=CelestialPhysics MechanicsToday and Dynamical Astronomy|date=2009-04-01September 1974 |volume=10327 |issue=49 |pages=365–37232–40 |doi=10.10071063/s10569-009-9203-81.3128863 |bibcode = 2009CeMDA1974PhT.103..365P.27i..32O |doi-access=free }}</ref><ref>{{cite web |title=The Lagrangian Points L4 and L5 |url=https://zenodopwg.gsfc.nasa.orggov/recordstargaze/1000691Slagrng2.htm |website=pwg.gsfc.nasa.gov |publisher=[[NASA]] |access-date=7 June 2021}}</ref> The [[L5 Society]] was founded to promote settlement by building space stations at these points in the Earth Moon system.

The {{L2}} point, on the [[far side of the Moon]], is completely shielded from Earth by the Moon so [[radio telescope]]s placed there would receive much less interference than existing telescopes. Of course, since the Moon is [[tidally locked]], any colony on the [[far side of the Moon]] has this same benefit; a lunar facility, however, would suffer from [[Moonquake]]s.

[[Gerard K. O'Neill]] suggested in 1974 that the Earth–Moon L₅ point, in particular, could fit several thousands of floating colonies, and would allow easy travel to and from the colonies due to the shallow [[effective potential]] at this point. A contemporary NASA team estimated that a 500,000-tonne colony would cost US$5.1&nbsp;billion (equivalent to US${{inflation|US|5.1|1974}}&nbsp;billion in {{Inflation/year|US}}) to build.<ref name="o'neill"/>

Both L1 and L2 require active [[stationkeeping]] since neither is fully stable (they are [[saddle point]]s on the energy landscape). Colonies at the {{L4}} and {{L5}} positions would have the advantage of being stable without any need for stationkeeping, and could be used as a waypoint for travel to and from [[cislunar space]].

O'Neill proposed manufacturing large [[O'Neill cylinder|cylinders]] or [[Bernal sphere|spheres]] as colony habitats, while others proposed an enclosed [[Stanford torus|torus]] shape or a huge [[Bishop Ring (habitat)|ring]] without a "roof". Another approach is to move an asteroid to a Lagrange point with a colony in its [[Terrarium (space habitat)|hollow]] interior.

In addition, they would significantly reduce the [[Delta-v#Delta-vs used for trajectories|delta-v]] (velocity change) needed to move from one to another, or to enter or leave Earth orbit, an important drawback of any lunar surface station, which demands [[Delta-v budget#Earth–Moon space budget|high energy expenditure]] to escape and a comparable or greater amount to soft-land.

==Sun–Earth==

[[Image:Lagrange points.jpg|thumb|right|330px|Contour lines of the effective potential illustrate the five Lagrange points of the Sun–Earth system]]

The L1 position is useful for solar observations since it is near Earth but in constant sunlight. It could also be useful for collecting solar power. Conversely, the L2 point is perpetually in the shadow of Earth, and as such offers a prime ___location for observing the [[outer planets]] or [[deep space exploration|deep space]]. L4 and L5 colonies could be used as [[waypoint]]s in space travel, to expand the practical [[launch window]] for travel to and from Earth and the other planets. These positions are useful for colonies as they are stable without any need for stationkeeping.

==Disadvantages==

{{POV section|date=August 2020}}

[[File:Structure_of_the_magnetosphere_LanguageSwitch.svg|lang=en|thumb|upright=1.5|Schematic of Earth's magnetosphere. The [[solar wind]] flows from left to right.]]

The risk of [[Proton#Human_exposure|proton exposure]] from the [[solar wind]] as well as the [[health threat from cosmic rays]] would be significant. The Earth's [[magnetosphere]] protects against solar storms but provides little protection from the more energetic cosmic radiation—the Earth's atmosphere protects us from that.{{cn|date=February 2018}}

In the Earth–Moon system, the orbit of colonies at L3–L5 would take them outside the protection of Earth's [[magnetosphere]] for approximately two-thirds of the time (as occurs with the Moon). Colonies at L1 (located between Earth and the Moon) would experience this to a lesser degree, whereas L2 (located beyond the Moon) would experience this to a greater degree and all of them would be exposed to the little-understood [[plasma sheet]] of the [[Magnetosphere#Magnetotail|magnetotail]].<ref>[http://www.nasa.gov/topics/moonmars/features/magnetotail_080416.html The Moon and the Magnetotail - Tony Phillips (2008)]</ref>

In the Sun–Earth system, L1 and L3–L5 are all outside the protection of Earth's magnetosphere. L2 periodically transfers from within the magnetotail, plasma sheet, and solar wind, depending on the intensity and direction of the solar wind.

Solar storm shielding would only be needed occasionally and it would also be easier to protect against in a shelter settlers could retreat to during a major storm. Cosmic radiation doses build up more slowly over years of exposure, and would need a couple of meters or more of shielding. Designs for space habitats usually supply this with an external shield of regolith or other materials.{{cn|date=February 2018}}

== See also ==

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*[http://www.esa.int/esaSC/SEMM17XJD1E_index_0.html European Space Agency]

*[https://web.archive.org/web/20070830061728/http://www.freemars.org/l5/aboutl5.html Free Mars]

*[http://www.orbitalvector.com/Space%20Structures/Lagrange%20Structures/LAGRANGE%20POINT%20STRUCTURES.htm Orbital Vector] {{Webarchive|url=https://web.archive.org/web/20170914225922/http://orbitalvector.com/Space%20Structures/Lagrange%20Structures/LAGRANGE%20POINT%20STRUCTURES.htm |date=September 14, 2017 }}

*[http://www.nasa.gov/topics/moonmars/features/magnetotail_080416.html NASA - The Moon and the Magnetotail] {{Webarchive|url=https://web.archive.org/web/20211114122639/https://www.nasa.gov/topics/moonmars/features/magnetotail_080416.html |date=November 14, 2021 }}

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