Model-Based Monitoring for Spacecraft Thruster Leakage

A report describes a method of detecting leakage in one of the 16 thrusters of the Cassini spacecraft. The detection method, implemented as part of the spacecraft flight software, is based on the fact that the three-axis rotational motion of a spacecraft is governed by the Euler's equation. The left-hand side of the Euler's equation contains both the inertia and gyroscopic torques, which are estimated by the attitude estimator of the attitude control software. The right-hand side of the Euler's equation contains reaction torques from both the thrusters and the reaction wheels which are also estimated.