Redundancy management of the Space Shuttle inertial measurement units

A description is given of the inertial measurement unit (IMU) redundancy management (RM) techniques for automatic in-flight monitoring of inertial instrument performance by the Space Shuttles primary onboard guidance, navigation, and control computers. The techniques and rationale for detecting and identifying faulty instruments are discussed. Special attention is given to the design philosophy, thresholds, and error propagation characteristics of the IMU RM system. The derivation of thresholds is described from the viewpoint of reliability and the safety of the vehicle and crew.