A gyroscope on a spacecraft that is used to provide attitude reference for the attitude and articulation control subsystem (AACS; see attitude control). The device is employed when celestial references, such as a star scanner or star tracker, are not in use. For example, the Galileo space probe would only activate its inertial reference device in the event of the loss of its celestial reference during certain manoeuvres. Other spacecraft, such as Magellan, made continuous use of the inertial reference device.
Subjects: Astronomy and Astrophysics.