Artist's depiction of a pair of O'Neill cylinders A pair of O'Neill cylinders (Island Three) 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.[1] O'Neill proposed the colonization of space for the 21st century, using materials extracted from the Moon and lat
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