Research On Fault Tolerant Control For Spacecrafts Proximity Rendevous

Diverse trends of space missions increase frequency of rendezvous and docking missions as well as importance of rendezvous and docking technology. To guarantee security and reliability of the system becomes a new subject since faults easily occur when spacecraft is vulnerable to interference running in harsh environment. This paper applied fault tolerant control to ensure successful completion of the rendezvous task considering actuator fault in the process of proximity rendezvous.In this paper, actuator fault-tolerant control is studied about attitude and orbit of spacecraft rendezvous, and the main work includes:Firstly, this paper gave relative attitude dynamics model in proximity rendezvous using Euler angles and rotation matrix parameters under actuator plus fault conditions, and established relative orbital model based on Cloheesy-Wilshire equation considering actuator plus faults.Based on the principle of orthogonality, Unscented Kalman Filter algorithm was improved by introducing suboptimal fading factors, and improved filtering algorithm has strong tacking properties. An augmented system was constructed, and using Strong Tracking Unscented Kalman Filter introducing suboptimal fading factors, the state and fault could be estimated at the same time. The simulation showed that the method gets fault estimation results quickly and accurately.Sliding mode control considering actuator saturation was chosen as passive fault-tolerant control to deal with actuator fault; then applied sliding mode control using additional fault estimation compensation term as active fault tolerant control to fulfill orbital tracking. Through horizontal comparison, we could conclude active fault-tolerant control has superiority of high control precision and strong fault-tolerant capability.To avoid unwinding phenomenon and discontinuous flywheel output, this paper defined a new attitude error function by the rotation matrix, and the new attitude error function could accurately describe relative attitude. On the basis of this description, a rotation matrix controller was designed. Combined with fault estimation, active fault tolerant controller was given. The simulation result indicated that active fault tolerant controller based on rotation matrix could get continuous actuator output, better control accuracy and fault tolerant effect.