Attitude Fault Tolerant Control Allocation For Over-actuated Spacecraft

External disturbance and uncertain satellite inertia will have certain e?ect on thesatellite attitude control performance. They may lead to the degradation of attitude con-trol performance. More specifically, the fault/failure occurring on satellite component willfurther degrade attitude control performance. It leads to the instability of the closed-loopsystem, and make the whole planned aerospace mission failure. As a result, satellite hasput forward higher requirements for the reliability of the attitude control system. Morespecifically, when sensors and actuators are faulty, the satellite should have capability tohandle those faults. Therefore, it is important to investigate the control design to handlesystem faults, and to guarantee the normal operation of the satellite. Although a num-ber of fault tolerant attitude control methodologies have been currently presented, theycan only tolerate component faults, while they can not handle system component con-figuration error. In practical engineering, there inevitably exists actuator misalignment.This issue will have a negative e?ect on the attitude control performance. On the otherhand, redundant actuators are usually installed to guarantee the reliability of the satellite.Therefore, the optimization problem of energy consumption should be addressed for over-actuated satellite. Consequently, taking actuator misalignment, multiple faults, externaldisturbance, uncertain inertia, and energy consumption problems into consideration, thisdissertation will investigate the attitude control of rigid satellite subject to degradationof actuator performance. The objectives of this study are to achieve high accuracy atti-tude control, optimization control of its energy consumption. The main contents of thisdissertation are presented as follows:Considering the planned on-orbital attitude maneuver and the problem of actuatorcontrol performance degradation, this study will firstly investigate the reason why thisdegradation is generated. On the basis of this, the mathematical model of satellite attitudecontrol system in the present of degradation of actuator performance is established. Somefundamental theory including support vector machine theory is also presented.Based on the established attitude control model with actuator fault taken into ac-count only, a fault estimation-based attitude stabilization approach is presented. It isdesigned by using the linearization of attitude model. In this approach, an observer isdesigned to estimate the error torque induced by actuator faults. By using this estimatedvalue, a nonlinear control law is then developed to compensate for its e?ect on the atti-tude control performance. High accuracy and stability of attitude control are achieved.More specifically, a time series-based control allocation method is also incorporated todistribute the commanded torque into each actuator. The objective of minimum consump-tion of energy is realized. It worth mentioning that, this method is designed based on thelinearized attitude model. In fact, such model may not precisely describe the attitude dy-namics. Hence, this model-based strategy may not get the perfect control performance.To solve this problem, another nonlinear observer-based active fault tolerant control ap-proach is designed. It is synthesized in the framework of fault estimation. It is shown byLyapunov stability theory that, this approach can stabilize the closed-loop attitude systemeven in the presence of external disturbance.For the over-actuated satellite subject to actuator fault and misalignment, a dynam-ic allocation-based attitude stabilization approach is proposed. External disturbance anduncertain inertia are considered. An adaptive law is first presented to estimate the systemuncertainties induced by the uncertain inertia. It is designed by using support vector the-ory. This scheme has capability to allocate the designed control torque into each actuatoroptimally. The optimization of energy consumption is thus achieved. Lyapunov stabilityanalysis and simulation results are presented to verify the e?ectiveness of this proposedapproach. Based on this control design, an adaptive variable fault tolerant control is fur-ther designed for an over-actuated satellite by redundant thrusters. It can achieve anygiven level of L2 gain control from the system input to its output. Hence, the attitudecontrol accuracy demanded by the planned mission can be achieved by tuning the controlparameters. Also, the designed control has the capability to achieve dynamic allocationof the desired control torque.Finally, an adaptive compensation control design methodology is proposed for over-actuated satellite. The degradation of actuator control performance and external distur-bance are mainly investigated. Finite-time attitude tracking control is achieved by thedesigned controller. In the control design, an adaptive compensation controller is first-ly designed for the reaction wheel controlling satellite. An adaptive law is designed toestimate the upper bound of the external disturbance and actuator performance degrada-tion. A control law is then designed by using this estimation to achieve attitude controlwith finite-time convergence. Because this method is inherently a passive fault tolerantcontrol, its controller has conservativeness. To address this drawback, a terminal slidingmode observer-based active fault tolerant controller is lastly developed. A sliding modeobserver is designed as the fault detection, isolation, and diagnosis mechanism. The totalerror torque induced by disturbance and actuator performance degradation is precisely es-timated. Then, a compensation controller is designed to compensate for this error torque,and to accomplish finite-time attitude tracking control. The attitude and the angular ve-locity tracking error are rigorously governed to zero in finite time. High attitude pointingaccuracy and attitude stability are guaranteed for attitude tracking maneuver.