An O'Neill cylinder is a space settlement concept proposed by American physicist Gerard K. O'Neill in his 1976 book The High Frontier: Human Colonies in Space. O'Neill proposed the colonization of space for the 21st century, using materials extracted from the Moon and later from asteroids.
Artist's depiction of a pair of O'Neill cylinders
Interior view, showing alternating land and window segments
Artist's impression of the interior of an O'Neill cylinder, showing the curvature of the inner surface
A NASA lunar base concept with a mass driver (the long structure that extends toward the horizon that is a part of the plan to build O'Neill Cylinders)
A space settlement is a settlement in outer space, sustaining more extensively habitation facilities in space than a general space station or spacecraft. Possibly including closed ecological systems, its particular purpose is permanent habitation.
A pair of O'Neill cylinders
Interior view of an O'Neill cylinder, showing alternating land and window stripes
A Stanford torus interior
Stanford torus exterior