A space habitat (also called a space settlement, space colony, spacestead, space city, orbital habitat, orbital settlement, orbital colony, orbital stead or orbital city) is a more advanced form of living quarters than a space station or habitation module, in that it is intended as a permanent settlement or green habitat rather than as a simple way-station or other specialized facility. No space habitat has been constructed yet, but many design concepts, with varying degrees of realism, have come both from engineers and from science-fiction authors.
The term space habitat sometimes includes more broadly habitats built on or in a body other than Earth—such as the Moon, Mars or an asteroid. This article concentrates on self-contained structures envisaged for micro-g environments.
A space habitat, or more precisely a space settlement, is any large-scale habitation facility in space, or more particularly in outer space or an orbit. A space habitat is typically designed to rotate so as to prevent long-term exposure of its residents to the peril of weightlessness or microgravity; studies have shown rotation to be a healthy substitute for gravity.
While not automatically constituting a colonial entity, a space habitat can be an element of a space colony. The term ’space colony’ has been viewed critically, prompting Carl Sagan to propose the term space city.
The idea of space habitats either in fact or fiction goes back to the second half of the 19th century. "The Brick Moon", a fictional story written in 1869 by Edward Everett Hale, is perhaps the first treatment of this idea in writing. In 1903, space pioneer Konstantin Tsiolkovsky speculated about rotating cylindrical space habitats, with plants fed by the sun, in Beyond Planet Earth. In the 1920s John Desmond Bernal and others speculated about giant space habitats. Dandridge M. Cole in the late 1950s and 1960s speculated about hollowing out asteroids and then rotating them to use as settlements in various magazine articles and books, notably Islands In Space: The Challenge Of The Planetoids.