AnO'Neill cylinder (also called anO'Neill colony, orIsland Three) is aspace settlement concept proposed by AmericanphysicistGerard K. O'Neill in his 1976 bookThe High Frontier: Human Colonies in Space.[1] O'Neill proposed thecolonization of space for the 21st century, using materials extracted from theMoon and later fromasteroids.[2]
An O'Neill cylinder would consist of two counter-rotating cylinders. The cylinders would rotate in opposite directions to cancel anygyroscopic effects that would otherwise make it difficult to keep them aimed toward the Sun. Each would be 6.4 kilometers (4 mi)[3] or 8.0 kilometers (5 mi)[4] in diameter and 32 kilometers (20 mi) long, connected at each end by a rod via abearing system. Their rotation would provideartificial gravity.[1]
While teaching undergraduatephysics atPrinceton University, O'Neill set his students on the task of designing large structures inouter space, with the intent of showing that sustainable living in space could be possible. 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 ofPhysics Today.[5]
O'Neill's project was not the first example of this concept. In 1954, German scientistHermann Oberth described the use of gigantic habitable cylinders for space travel in his bookMenschen im Weltraum—Neue Projekte für Raketen- und Raumfahrt (People in Space—New Projects for Rockets and Space Travel). In 1970, science-fiction authorLarry Niven proposed a larger-scale concept in his novelRingworld. Then, three years before O'Neill proposed his cylinder,Arthur C. Clarke used such a habitable cylinder (albeit of extraterrestrial construction) in his novelRendezvous with Rama.
In his 1976 book[1] O'Neill described three reference designs, nicknamed "islands":
To save the immense cost of rocketing the materials from Earth, these habitats would be built with materials launched into space from the Moon with a magneticmass driver.[1]
In the September 1974 edition ofPhysics Today magazine, Dr. O'Neill argued that life on board an O'Neill cylinder would be better than some places on Earth.[8] This would be because of an abundance in food, climate and weather control, and the fact that there would be no need for vehicles that use combustion engines that would create smog and pollution.[8] The inhabitants would also keep themselves active and entertained by practicing current earth sports such as skiing, sailing, and mountain climbing, thanks to artificially generated gravity due to the cylinder's rotation. In addition to these sports, new sports would also be created out of the habitat being enclosed in a cylinder in space, and these circumstances would be creatively taken advantage of.[8]
The cylinders rotate to provideartificial gravity on their inner surface. At the radius described by O'Neill, the habitats would have to rotate about twenty-eight times an hour to simulate a standard Earthgravity; anangular velocity of 2.8 degrees per second. Research on human factors in rotating reference frames[9][10][11][12][13] indicate that, at such low rotation speeds, few people would experiencemotion sickness due tocoriolis forces acting on the inner ear. People would, however, be able to detect spinward and antispinward directions by turning their heads, and any dropped items would appear to be deflected by a few centimetres.[12] The central axis of the habitat would be azero-gravity region, and it was envisaged that recreational facilities could be located there.
Note that a single isolated cylinder, as depicted in theBabylon 5 series, would be dynamically unstable.
The habitat was planned to have oxygen atpartial pressures roughly similar to terrestrial air, 20% of the Earth's sea-level air pressure. Nitrogen would also be included to add a further 30% of the Earth's pressure. This half-pressure atmosphere would save gas and reduce the needed strength and thickness of the habitat walls.[1][6]
At this scale, the air within the cylinder and the shell of the cylinder provide adequate shielding againstcosmic rays.[1] The internal volume of an O'Neill cylinder is great enough to support its own small weather systems, which may be manipulated by altering the internal atmospheric composition or the amount of reflected sunlight.[7]
Large mirrors are hinged at the back of each stripe of window. The unhinged edge of the windows points toward the Sun. The purpose of the mirrors is to reflectsunlight into the cylinders through the windows. Night is simulated by opening the mirrors, letting the window view empty space; this also permits heat to radiate to space. During the day, the reflected Sun appears to move as the mirrors move, creating a natural progression of Sun angles. Although not visible to the naked eye, the Sun's image might be observed to rotate due to the cylinder's rotation. Light reflected by mirrors ispolarized, which might confuse pollinatingbees.[1]
To permit light to enter the habitat, large windows run the length of the cylinder.[1] These would not be single panes, but would be made up of many small sections, to prevent catastrophic damage, and so the aluminum or steel window frames can take most of the stresses of the air pressure of the habitat.[1] Occasionally a meteoroid might break one of these panes. This would cause some loss of the atmosphere, but calculations showed that this would not be an emergency, due to the very large volume of the habitat.[1]
The habitat and its mirrors must be perpetuallyaimed at the Sun to collect solar energy and light the habitat's interior. O'Neill and his students carefully worked out a method of continuously turning the colony 360 degrees per orbit without using rockets (which would shed reaction mass).[1] First, the pair of habitats can be rolled by operating the cylinders asmomentum wheels. If one habitat's rotation is slightly off, the two cylinders will rotate about each other. Once the plane formed by the two axes of rotation is perpendicular in the roll axis to the orbit, then the pair of cylinders can beyawed to aim at the Sun by exerting a force between the two sunward bearings. Pushing the cylinders away from each other will cause both cylinders to gyroscopicallyprecess, and the system will yaw in one direction, while pushing them towards each other will cause yaw in the other direction. The counter-rotating habitats have no netgyroscopic effect, and so this slight precession can continue throughout the habitat's orbit, keeping it aimed at the Sun. This is a novel application ofcontrol moment gyroscopes.
In 1990 and 2007, a smaller design derivative known as Kalpana One was presented, which addresses the wobbling effect of a rotating cylinder by increasing the diameter and shortening the length. The logistical challenges ofradiation shielding are dealt with by constructing the station inlow Earth orbit and removing the windows.[14][15]
In 2014, a new construction method was suggested that involved inflating a bag and taping it with a spool (constructed from asteroidal materials) like the construction of acomposite overwrapped pressure vessel.[16]
At aBlue Origin event in Washington on May 9, 2019Jeff Bezos proposed building O'Neill colonies rather than colonizing other planets.[17][18]
![A cylinder constructed from interconnected bolas or other geometries[19]](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aCurreri_space_habitat_evolution.png)
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Notes: † Never inhabited due to launch or on-orbit failure, ‡ Part of theAlmaz military program, ° Never inhabited, lacks docking mechanism. | |||||||||