Gyroscope

A disc with a heavy rim mounted in such a way that its axis of rotation can adopt any position. Once the disc is spinning, the rotation axis remains fixed with reference to fixed stars, which makes the gyroscope useful for determining movement away from a fixed course.

Three gyroscopes rotating about perpendicular axes help to maintain the orientation of a spacecraft in space by detecting rotation about any of the axes and initiating a mechanism to correct it.

See also: Gimbal, Precession, Precession Vector, Sagnac Effect, Turn Error.