Maximum Likelihood Failure Detection Techniques Applied to the Shuttle RCS Jets

A software technique for onboard detection and identification of hard failures and leaks of the shuttle orbiter reaction control subsystem jets during the orbital flight phase is presented. The method uses only the gimbal angle and linear velocity measurements available from the orbiter inertia! measurement unit. The system produces rotational state estimates required by the attitude autopilot in addition to performing failure identification. Uncoupled steady-state constant covariance extended Kalman filters with residual traps are employed for rotational and translational state estimation, and generalized likelihood ratio tests are made for failure identification. Rigid body simulation results indicate station-level identification times of less than 2 sec for primary jet hard failures and less than 70 sec for vernier jet hard failures and primary jet leaks.