Artificial gravity

Artificial gravity, also known as pseudo-gravity, is the theoretical increase or decrease of apparent gravity (g-force) by artificial means, particularly in space, but also on Earth. It can be practically achieved by the use of different forces, particularly the centripetal force and linear acceleration.

The creation of artificial gravity is considered desirable for long-term space travel or habitation, for ease of mobility, for in-space fluid management, and to avoid the adverse long-term health effects of weightlessness.

A number of methods for generating artificial gravity have been proposed, as well as an even larger number of science fiction approaches using both real and fictitious forces. Practical outer space applications of artificial gravity for humans have not yet been built and flown, principally because of the large size of the spacecraft required to produce centripetal acceleration.

Requirement for gravity

Without g-force, space adaptation syndrome occurs in some humans and animals. Many adaptations occur over a few days, but over a long period of time bone density decreases, and some of this decrease may be permanent. The minimal g-force required to avoid bone loss is not known—nearly all current experience is with g-forces of 1 g (on the surface of the Earth) or 0 g in orbit. There has not been sufficient time spent on the Moon to determine whether lunar gravity is sufficient.

Artificial gravity (fiction)

Artificial gravity is a common theme in fiction, particularly science fiction.

Rotational gravity

In the movie 2001: A Space Odyssey, a rotating centrifuge in the Discovery spacecraft provides artificial gravity. The people would be walking inside the circle; their feet toward the exterior and their head toward the center, the floor and ceiling would curve upwards. A rotating circular set was used in at least one instance to make this effect with the actors always at the bottom; as they walked, the set would be turned to keep the actors at the bottom and prevent them from falling over as they walked up the curved floor. The movie also features a rotating space station.

Larry Niven's novel Ringworld featured a gigantic habitat encircling a star, which created artificial gravity through rotation. Niven also makes a reference to the Coriolis effect when the protagonists see what looks like a giant eye above the horizon. When they get closer, they realise that it is in fact a hurricane, but rotating about an axis parallel to the ground rather than perpendicular to it. Large hurricanes on Earth rotate the way they do due to the Coriolis effect. A number of early Known Space and Man-Kzin Wars stories also make use of rotational gravity, prior to the adoption of "gravity polarizer" technology which generates artificial gravity fields.