The O'Neill cylinder is essentially a space settlement design proposed by American physicist Gerard K. O'Neill in his 1976 book The High Frontier: Human Colonies in Space. An O'Neill cylinder would consist of two counter-rotating cylinders. The cylinders would rotate in opposite directions in order to cancel out any gyroscopic effects that would otherwise make it difficult to keep them aimed toward the Sun. Each would be 5-miles in diameter and 20-miles long, connected at each end by a rod via a bearing system. They would rotate so as to provide artificial gravity via centrifugal force on their inner surfaces. Continue reading for two more videos, pictures and additional information.