Spacecraft Attitude Fault-tolerant Control Methods With Actuator Fault

There are more than 4000 spacecrafts which have been launched around the world in the past 25 yearrs. Spacecraft play an increasingly important role in various areas of modern society, such as telecommunication, Earth observation, and space exploration. Despite rigorous testing, many of these spacecraft fail on orbit due to various reasons, such as scurviness space environment. Due to a report of Canadian Space Agency, over 30% of spacecraft failures occur at the subsystem level of the attitude and orbit control system(AOCS). Moreover, about 50% of the AOCS failures are attributed to actuator errors. The purpose of this paper is to present an actuator fault-tolerant attitude control. In this paper, the spacecraft is designed according to the traditional satellite design method, which assumes that the satellit is designed for a single use and cannot be upgraded or serviced. A futher comprehensive research is studied on the spacecraft attitude control system with actuator failures on both theoretical and adhibition.Currently, there are few active fault-tolerant control method to solve the actuator failure of spacecraft attitude control systeme with good performance. The overcome difficulties including but not limited to nonlinear attitude dynamic model establishment, the rapid response capability improvement, the output control torque limit, and unknown actuator failures. To solve these problems, this paper focus on design fault-tolerant control scheme of the spacecraft attitude control system. To verify the proposed fault-tolerant control scheme of the spacecraft attitude control system is effective: one is by using Lyapunov function to analysis the global stability of the closed loop system; the other is by numerical simulation to verify the control performance of the fault-tolerant control scheme for its validity and feasibility.A backstepping control scheme is designed by taking into account the partial loss failure of the spacecraft actuator. First of all, a global stability fault-tolerant control scheme is designed based on Lyapunov function under the spacecraft attitude control system model without fault; then, disscuss on the different procedures for defining the component of the Lyapunov fuction is related to the general one of potential shaping for mechanical systems. In this paper a purely geometric approach is used to define a Lyapunov function where the error measure used to define the Lyapunov function corresponds to the topology of the error space; Finally, simulate and compare with the attitude control method widely used, and determine the adaptive backstepping control scheme has quicker responsed time and better fault tolerance under both constant fault and time variant fault.An adaptive sliding mode control strategy based on global sliding mode control theory is proposed for the spacecraft attitude control system with actuator gain fault(partial loss and complete failure). First, in view of there is no actuator redundancy available, and each actuator may lose its effectiveness partially. An attitude control system based on variable structure control is developed that guarantees asymptotical stability for the spacecraft attitude control system. This is then extended to handle the case with actuator redundancy, where some of the actuators fail completely. A key feature of the proposed strategy is that the design of the fault-tolerant control is independent of the information about the faults. Using the Lyapunov method, the overall system stabilisation and fault tolerance are ensured, and the benefits of the proposed control methods are verified analytically and validated via a simulation study.Finally, an adaptive fault tolerant control method based on reference model is proposed, which is avalible for the spacecraft attitude control system with combined actuator faults(gain fault and deviation fault). An nonlinear ideal reference model is built to identify an actuator fault, where a fault is identified when the real system deviates from the ideal model. The control tracks the controlled ideal reference model to replicate it as closely as possible. Two adaptive parameters are used that increase the responsiveness of the tracking control to deviations from the ideal reference state. Moreover, the proposed control design methods do not require any system identification process to identify the faults or any method of fault detection and isolation. Through comparing the proposed adaptive control to a conventional proportional controller, we can see the adaptive control demonstrates an improved control performance.