Lagrange point colonization
# Lagrange point colonization

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

The Lagrange points $L_4$ and $L_5$ are stable if the mass of the larger body is at least 25 times the mass of the secondary body. Thus, the points $L_4$ and $L_5$ in the Earth–Moon system have been proposed as possible sites for space colonies. 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 $L_5$ 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.

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.

