Rotating Space Habitats

Heaven Habitat2
Image from Anders Sandberg
Heaven Habitat (see left) was built in Earth Orbit in the late 21st century using expended heavy-lifter fuel tanks. The 36 modules were connected using polycarbon cables and rotated together in order to simulate 0.5 G.

When humankind first went into space an early priority was the construction of space habitats. The first examples of such habitats were constructed with no attempt to provide artificial gravity; and zero gravity habitats continue to be very common, especially among the microgravity-adapted clades such as the Space-adapted Humans and associated subtypes. One useful type of zero-gee habitat was the Bigelow inflatable structure, made of flexible but strong cloth-like materials. However for the comfort of the majority of planet-dwelling peoples it was desirable to replicate the effects of gravity in some way.

Centrifugal gravity produced by rotating the habitat was adopted early in the Interplanetary age, and continues to be the method used almost exclusively throughout the Terragen Sphere. Some habitats and spacecraft use utility fog and other mechanical forms of restraint to replicate some of the effects of gravity; this method does not provide any acceleration effects, so the medical effects of freefall are still apparent and need to be treated.

Centrifugal gravity is produced by rotation around a single axis. To reduce coriolis effects and for comfort's sake, most habitats rotate no more than 3 times per minute (3 rpm). To replicate one standard Earth gravity a habitat rotating at 3 rpm would need to be 99.3 metres in radius. In practice many small habitats use a lower gravity regime, and can therefore have a smaller radius or a slower rotation; a very popular gravity strength for nearbaseline human clades is 0.8 gees, which is high enough to be perfectly comfortable, but low enough to reduce strain on the inhabitants' bodies during normal activities.

Even lower gravities are commonplace in the large, slowly-rotating worlds known as Ribbonworlds, which are generally favoured by flying and leaping clades and bodymorphs.

Because centrifugally produced gravity acts directly away from the axis of rotation, the designs used are limited to a few basic forms. Two modules can be linked by tether and rotated around a centre of gravity; this is the simplest form. If several such modules are connected together they form a ring, for instance in the very early Heaven Habitat shown above.

Although the archailects in the Orion's Arm have exquisite control over spacetime curvature and could produce a gravity field within a habitat or other vessel if they found such a thing necessary, there are very many physical and practical problems with such fields and in practice such effects are rarely used in habitats and vessels used by modosophonts.

Common designs of rotating space habitat which have been used for many thousands of years include (in order of increasing size) the Stanford Torus, the Bernal Sphere, the O'Neill Island Three cylinders, the Bishop Ring and the McKendree Cylinder.

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Development Notes
Text by Steve Bowers
Initially published on 27 August 2008.

An essay about the Coriolis Effect in a Rotating Space Habitat by Grant Hutchison.

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