Lagrange point colonization

{{Short description|Colonization of five equilibrium points in the orbit of planets or moons}}

{{Use American English|date=November 2020}}

{{Use mdy dates|date=November 2020}}

Image:Lagrange points Earth vs Moon.jpgs 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.]]

Lagrange point colonization is a proposed form of space colonization{{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}} of the five equilibrium points in the orbit of a planet or its primary moon, called Lagrange points.

The Lagrange points {{L4}} and {{L5}} are stable if the mass of the larger body is at least 25 times the mass of the secondary body.{{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}}{{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}} Thus, the points L₄ and L₅ in the Earth–Moon system have been proposed as possible sites for space colonies.{{cite journal |last1=O'Neill |first1=Gerard K. |author1-link=Gerard K. O'Neill |title=The colonization of space |journal=Physics Today |date=September 1974 |volume=27 |issue=9 |pages=32–40 |doi=10.1063/1.3128863 |bibcode=1974PhT....27i..32O |doi-access=free }}{{cite web |title=The Lagrangian Points L4 and L5 |url=https://pwg.gsfc.nasa.gov/stargaze/Slagrng2.htm |website=pwg.gsfc.nasa.gov |publisher=NASA |access-date=7 June 2021}} The L5 Society was founded to promote settlement by building space stations at these points.

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$5.1 billion (equivalent to US${{inflation|US|5.1|1974}} billion in {{Inflation/year|US}}) to build.

O'Neill proposed manufacturing large cylinders or spheres as colony habitats, while others proposed an enclosed torus shape or a huge ring without a "roof". Another approach is to move an asteroid to a Lagrange point with a colony in its hollow interior.