|Bishop ring interior|
Giant rotating orbital habitat, built of woven diamondoid/buckyfibre cable; often around 2000 km in diameter and 500 km deep, open to space so that air is retained through centrifugal motion (and a thin membrane).
When carbon nanotube buckyfibre cable became readily available through nanofacturing techniques, the size of rotating habitats could be increased considerably. The largest rotating habitats possible using this material can be somewhat more than one thousand kilometers in radius, depending on the mass of landscape included. In the Information Age Forrest Bishop proposed this design of ring-shaped, open ended habitat, with the atmosphere retained by centrifugal force and tall atmosphere walls.
The ring is constructed from a coil or weave of carbon nanotube buckytube, formed into a short cylinder which is rotated to produce artificial gravity. Carbon Nanotube is sufficiently strong to support a cylinder of around 2000km in diameter with a rotation producing 1 gravity, but this leaves little margin for safety, and does not allow for the mass of the artificial landscape inside the ring. So most rings with Earth-like gravity are significantly smaller, from a few hundred up to a thousand kilometres in diameter. However a significant number of rings rotate more slowly, producing a lower gravity regime (a condition which is often popular with the inhabitants). The Arkab B necklace, for example, consist mostly of rings around 2000km across and an internal gravity of 0.8 gees or less.
This coil, or weave, is used to reinforce the main bulk of the ring, which holds atmosphere, soil, water, rocky substrate and habitations. In most versions of the Bishop Ring design, the bulk of the atmosphere is retained by a tall atmosphere wall ranging in height from 50km to 200km. Even 200km high walls are not high enough to prevent gradual atmosphere loss, so a thin transparent membrane or an airwall is used to cut atmospheric escape to negligible levels.
Generally the local star is permanently obscured from the point of view of someone standing on the ring-floor, to avoid constantly shifting illumination effects. This means the ring requires artificial lighting, generally provided by a central artificial sunlet called a luminaire. Power for this luminaire can be collected by photovoltaic cells on the outside of the ring; if the ring is distant from the star, the p-v arrays can be extended beyond the ring floor in both directions, and/or other sources of energy can be utilised.
One clade associated with the construction of Bishop Rings are the vac-spider species Hobo Sapiens, who can extrude a range of specialised buckyfibre filaments from their spinerettes.