The Stanford torus is a proposed NASA design for a space habitat capable of housing 10,000 to 140,000 permanent residents. The Stanford torus was proposed during the 1975 NASA Summer Study, conducted at American elite university Stanford University, with the purpose of exploring and speculating on designs for future space colonies (Gerard O'Neill later proposed his Island One or Bernal sphere as an alternative to the torus).
"Stanford torus" refers only to this particular version of the design, as the concept of a ring-shaped rotating space station was previously proposed by Wernher von Braun and Herman Potočnik. It consists of a torus, or doughnut-shaped ring, that is 1.8 km in diameter (for the proposed 10,000 person habitat described in the 1975 Summer Study) and rotates once per minute to provide between 0.9g and 1.0g of artificial gravity on the inside of the outer ring via centrifugal force. Sunlight is provided to the interior of the torus by a system of mirrors.
The ring is connected to a hub via a number of "spokes", which serve as conduits for people and materials travelling to and from the hub. Since the hub is at the rotational axis of the station, it experiences the least artificial gravity and is the easiest location for spacecraft to dock. Zero-gravity industry is performed in a non-rotating module attached to the hub's axis. The interior space of the torus itself is used as living space, and is large enough that a "natural" environment can be simulated; the torus appears similar to a long, narrow, straight glacial valley whose ends curve upward and eventually meet overhead to form a complete circle. The population density is similar to a dense suburb, with part of the ring dedicated to agriculture and part to housing.