O'Neill cylinder

The O'Neill cylinder (also called an O'Neill colony) is a space settlement design 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 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 (8.0 km) in diameter and 20 miles (32 km) 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.

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 by O'Neill in a September 1974 article of Physics Today.

O'Neill's project was not completely without precedent. In 1954, the German scientist Hermann Oberth described the use of gigantic habitable cylinders for space travel in his book Menschen im Weltraum – Neue Projekte für Raketen- und Raumfahrt ("People in space – New projects for rockets and space travel").

O'Neill created three reference designs, nicknamed "islands":

Island One is a rotating sphere measuring one mile in circumference (1,681 feet or 512.27 meters in diameter), with people living on the equatorial region (see Bernal sphere). A later NASA/Ames study at Stanford University developed an alternative version of Island One: the Stanford torus, a toroidal shape 1,600 metres (5,200 ft) in diameter.

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