Model-based Fault Diagnosis For Satellite Attitude Control System

Satellite attitude control system is the key subsystem to complete satellitecontrol. When the satellites are working in the space, the failures of the attitudecontrol system often occur. To ensure the safe and stable operation, it isnecessary to research fault diagnosis method for the satellite attitude controlsystem. In this article, the quantitative model based fault diagnosis method isproposed to diagnose the possible fault of satellite attitude control system.The mathematical model of attitude control system for earth-orientedthree-axis stabilized satellite is established. And the corresponding fault modelsare established for the components which may be fault, including the flywheel,gyro and star sensor. By the use of the Matlab/simulink, the simulation analysishas been done to research the operation of the satellite under the normal and faultstates.The fault detection observer for satellite actuator is designed usinganalytical redundancy provided by attitude dynamic. And the ability for detectingflywheel fault has been simulated and analyzed. Based on the nonlinear unknowninput observer which can decouple disturbance, the dedicated observer has beendesigned to decouple the flywheel fault on each axis. The isolation of the faultflywheel has been realized. Through the simulation, fault isolation has beenverified and analyzed.Fault detection observer is designed for gyro using analytical redundancyprovided by satellite attitude kinematic. And simulations analyze its validity.Based on the principle of nonlinear adaptive observer, dedicated observer fordiagnosing gyro fault has been designed. The simulation results show that, forconstant drift fault, which axis the fault gyro on can be separated, and the valueof the drift can be estimated.Fault isolation strategies based on observers redundancy has been putforward. The fault of the flywheel, gyro or star sensor can be detected correctly.From the view of the system-level, a complete strategy for fault diagnosis ofsatellite attitude control system has been designed. The quantitative model basedfault diagnosis strategy for the satellite control system realize in two step: thefault detection and fault isolation.