Lagrange point colonization

Lagrange point colonization is a proposed form of space colonization[1] of the five equilibrium points in the orbit of a planet or its primary moon, called Lagrange points.

A diagram showing the five Lagrange points 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 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.[2][3] Thus, the points L₄ and L₅ in the Earth–Moon system have been proposed as possible sites for space colonies.[4][5] 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$30 billion in 2022) to build.[4]

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.