O'Neill cylinder

The O'Neill cylinder also called Island Three is a space habitat design proposed by physicist Gerard K. O'Neill in his book, The High Frontier. In the book O'Neill proposes the colonization of space for the 21st century, using materials from the Moon.

An Island Three consists of two very large counter rotating cylinders, 3 km radius and 20 km long, that are connected at each end by a rod via a bearing system. They rotate so as to provide spin gravity on their inner surfaces.

Background

While teaching undergraduate physics at Princeton University he had students design large structures in space, with the intent to show that living in space could be desirable. Several of the architectures were able to provide areas 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 1974 article in Physics Today.

Islands One, Two and Three

O'Neill has created three reference designs:Island One

A sphere measuring one mile in circumference (1,681 feet or 512.27 meters in diameter) which rotated, and people lived on the equatorial region. See Bernal Sphere.

A later NASA/Ames study at Stanford University developed an alternate version of Island One: the Stanford torus geometry, a toroidal shape 1,600 meters (just under a mile) in diameter.Island Two

Also a sphere, also 1,600 meters in diameter.Island Three

Two counter-rotating cylinders each two miles (3 km) in radius, and capable of scaling up to twenty miles (30 km) long. Each cylinder has six equal-area stripes that run the length of the cylinder; three are windows, three are "land." Furthermore, an outer agriculture ring, as seen in the picture on the right, 10 miles (15 km) in radius, rotates at a different speed for farming. The manufacturing block is located at the middle (behind the satellite dish assembly) to allow for minimized gravity for some manufacturing processes.

These habitats were to be built with materials launched into space with a kind of magnetic catapult called a mass driver.

Artificial gravity

The cylinders rotate to provide artificial gravity on their inner surface. Due to their very large radii, the habitats would rotate about forty times an hour, simulating a standard Earth gravity. NASA experiments in rotating reference frames indicate that almost no-one (at such low rotation speeds) would experience motion sickness due to coriolis forces acting on the inner ear. People would be able to detect spinward and antispinward directions by turning their heads, however, and dropped items would appear to be deflected by a few centimetres.

The central axis of the habitat would be a zero gravity region, and it was envisaged that it would be possible to have recreational facilities located there.

Atmosphere and radiation

The habitat was intended to use a reduced air pressure of about half Earth sea-level. This saved gas as well as reducing the necessary thickness of the habitat walls.

At this scale, the air within the cylinder and the shell of the cylinder provide adequate shielding against cosmic rays.

Sunlight

To permit light to enter the habitat, large windows run the length of the cylinder. These were not to be single panes, but would be made up of individual sections, of considerable thickness, so as to be able to handle the pressure of the atmosphere in the habitat. Occasionally a meteorite would break one of these panes, which 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.

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 reflect sunlight 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. As an aside, the light reflected from the mirrors is polarized, which might confuse bees.

Attitude control

Although the counter-rotating habitats have no gyroscopic effect, it's highly desirable to be able to control the pointing ("attitude") of the habitats to keep the mirrors correctly angled towards the sun. To do this, O'Neill and his students carefully worked out a method of aiming the habitats. First, the pair of habitats can be rolled by operating the cylinders as momentum wheels. If one habitat's rotation is slightly retarded, 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 be yawed to aim at the sun by exerting a force between the two sunward bearings: away from each other will cause both cylinders to gyroscopically precess, and the system will yaw in one direction, towards each other will cause yaw in the other direction.

See also

• Dyson Sphere
• Bernal sphere
• Centrifuge Accommodations Module
• Globus Cassus
• Stanford torus
• Space stations and habitats in popular culture

References

• O'Neill, Gerard K. (1977). The High Frontier: Human Colonies in Space. William Morrow & Company. ISBN 0-688-03133-1.