An O'Neill cylinder (also called an O'Neill colony) 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.
An O'Neill cylinder would consist of two counter-rotating cylinders. The cylinders would rotate in opposite directions to cancel any gyroscopic effects that would otherwise make it difficult to keep them aimed toward the Sun. Each would be 5 miles (8.0 km) in diameter and 20 miles (32 km) long, connected at each end by a rod via a bearing system. Their rotation would provide artificial gravity.
Background
While teaching undergraduate physics at Princeton University, O'Neill set his students the task of designing large structures in outer space, with the intent of showing that living in space could be desirable. Several of the designs were able to provide volumes large enough to be suitable for human habitation. This cooperative result inspired the idea of the cylinder and was first published...