A space habitat, also called space colony and orbital colony, is a space station which is intended as a permanent settlement rather than as a simple waystation or other specialized facility. They would be literal "cities" in space, where people would live and work and raise families. No space habitats have yet been constructed, but many design proposals have been made with varying degrees of realism by both science fiction authors and engineers.

Most of the real work on space habitats was carried out in the 1970s by workshops led by Gerard K. O'Neill in the post-Apollo highs at NASA. Several designs were studied, some in depth, with sizes ranging from 1,000 to 10,000 people. Attempts were made to make the habitats as self-supporting as possible, but all of the designs relied on regular shipments from Earth or the Moon, notably for volatiles. However, more recent research has indicated that certain asteroids contain significant amounts of volatiles such as water and ammonia, making it possible to reduce this reliance considerably.

One problem with the design that was not considered in any real depth is why any of them would be needed. The stated problem was to house workers needed for the construction of solar power satellites, which they predicted would require a peak of about 25,000 workers. However if this was the purpose, the habitat designs were certainly not utilitarian; they all contained housing for complete families, huge open spaces, and considerable parkland. An oil platform would appear to be a better model for such purposes. The workshops appeared to work in reverse, inventing the "solution", and then casting about for a need. Of course, this objection applies to colonies located on planets and moons as well.

Reasons for space colonisation: space. Lots of space. As there exists a vast amount of material to build with in the solar system, and as a space habitat is out of planetary gravity wells, a vast population(100's of billions if not trillions) could live and work in space permanently. The Earth can be viewed as quite small, crowded and restrictive compared to outer space. see: overpopulation.

People have advocated that before humans send a generation ship to the stars, we should create large self-sustaining space habitats first. Each space habitat would be isolated from the rest of humanity for a century, but near enough to Earth for help. This would test if thousands of humans can survive a century on their own before sending them beyond the reach of any help.

Designs proposed include:

• Bernal sphere - "Island One"
• Stanford torus - "Island Two"
• O'Neill cylinder - "Island Three"

The Lagrangian points in the solar system have been suggested as suitable locations.

See also

• Transhab