Spacecraft Attitude Fault-Tolerant Control Under Actuator Failures And Misalignment

With the developing of aerospace technology,the research of spacecraft,as the supporter of space mission,is brought into more and more focus by researchers related.Since human’s thousands of space explorations in decades,there are increasing number of space debris.Add to the rocks exists in space and the bad working environment in space,to ensure the safety for in-orbit spacecraft operation is harder and harder.So there is a practical implication value to make spacecraft attitude control system stable.As the most important part of spacecraft attitude control,Actuator is the key to the stability of spacecraft attitude control.If failures happens on actuators,there is a possibility to lead the failure of a whole aerospace mission.So taking actuator failures into account is significant to the stability for control system.Meanwhile,due to the manufacturing technique and severe vibration during the spacecraft launching,actuators will lead inevitable misalignment.This misalignment will cause the error between actual output torque and expected output torque.If this misalignment is not taken into account,the control torque will not operate properly,which will finally rise up to instability to whole attitude control system.The electromagnetic interference and all kinds of uncertain disturbance torque brought by the bad working environment in space will affect the stability of attitude control system as well.There are many researches about spacecraft attitude fault-tolerant control and many control methods proposed,but few of them take actuator failures and its misalignment,disturbance torque and uncertain rotational inertia all into account.So there is a need to raise a robust control method to make spacecraft attitude system control itself in limited time autonomously.This paper takes overdrive spacecraft with four flywheels as the research object.First,considering the disturbance torque and the actuator failures,a sliding mode robust fault-tolerant control method,with a sequence motif optimum control allocation method is proposed.This strategy can make sure for the stability of attitude control system and allocating control torques into redundant flywheels.Then actuator misalignment and uncertain rotational inertia are taken into account,and self-adapting attitude compensatory tracking controller with a dynamic control allocation method based on dynamic allocation theorem is proposed.This strategy can make sure that spacecraft will implement self adaption control in real time online to maintain the attitude control system stable in orbit.The strategies above are proved by Lyapunov stability theorem,and testified effective by MATLAB numerical simulation.