Orbital (space habitat)
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In Iain M. Banks' fictional Culture universe, an Orbital is a purpose-built space habitat.
Banks has described them as looking like "a god's bracelet" hanging in space. Orbitals are ribbon-like hoops of superstrong material (see also unobtainium) reinforced and joined with forcefields. On the inside of the hoop, there can be any type of planetary environment, from desert to ocean to jungle to glacier. At the edges are high walls to keep the atmosphere in and protect the inhabitants from radiation, typically tens or hundreds of kilometres high.
Orbitals spin to mimic the effects of gravity, and are sized so that the rate of rotation necessary to produce a comfortable gravity level is approximately equal to one day. In the case of the standard Culture day and gravity, this diameter is around fourteen million kilometres. By tilting the axis of the Orbital relative to its orbit around a star, a convenient day-night cycle can be experienced by the inhabitants.
The Culture's Orbitals are each governed/managed by a Mind, which is situated in a structure in space at the centre of the Orbital, known as the Hub. The Mind is generally referred to simply as "Hub" by the inhabitants of the Orbital. Other civilisations also build Orbitals, however, and it is not clear that all are so-managed.
An Orbital is similar to a Ringworld, but is much smaller and does not enclose its primary star within itself, instead orbiting the star in a more conventional manner.
It should also be noted that the computer game Halo: Combat Evolved by Bungie Studios is set on a structure similar to an Orbital, only much smaller, only ten thousand kilometres across.