Space Cities

Habitats in stationary locations above a planet

Space City
Image from Steve Bowers
New Phoenix City, suspended on eighteen space fountains above Florizel

The term 'space city' has traditionally been reserved for habitats suspended above a particular location on a planet. One of the first habitats to identify itself as a space city was Supra-Tokyo, located in geostationary orbit above the Pacific ocean on Old Earth. Many habitats in Clarke Rings take the name of cities or other locations on the planet beneath them.

However stationary orbits are located at a relatively large distance from the planet below. Even if a beanstalk is present, the journey time between the planet and such habitats can be significant. However mass-beam technology can be used to establish structures and habitats much closer to the planet's surface.

City Rings

Venus after terraforming
Image from Steve Bowers
Venus after Terraforming; the cityring, built using atmospheric carbon, can be seen
A set of dynamic orbital rings can be used to support stationary habitats at a arbitrary height above a planet. Mass-streams, moving faster than orbital speed within magnetic tracks, will exert an outward pressure in such a ring, may or may not be stationary above the planet below. Any number of space cities may be located on such a ring, depending on their mass and the available energy; frequently the ring will become a continuous city-ring, supporting habitable structures along its length.

Space Fountain
Image from Anders Sandberg
More recently more advanced space cities have been built in various locations, supported by multiple space fountains. Massive loops of particle beams are used to support small, lightweight cities above the atmosphere, using superconducting materials to redirect the beams back towards the planet. The total momentum of such fountains is very large; nevertheless the mass of the city (or other payload) will generally not exceed 2% of the total mass of the support system.

One downside to stationary habitats of this kind is that they move far below orbital speed, so any spacecraft leaving them will need to accelerate rapidly in order to travel into space. City rings and other orbital ring systems can support lengthy acceleration tracks, allowing relatively easy access to orbit; but space fountains and cities supported by them are generally too small to allow this sort of acceleration. Sometimes a static orbital ring may be used to allow easy access to space from such structures.
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Development Notes
Text by Steve Bowers
Mike Miller and Alex Mulvey
Initially published on 23 March 2015.