Attitude Control Allocation Research For Over-actuated Spacecraft System

Realizing accurate and reliable attitude stabilization is one of the most important andcritical problems in spacecraft attitude control research fields recently. For orbiting spacecraft,the dynamics is strong nonlinear and coupled in nature and affected by parametersuncertainties and various disturbances. In addition, the actuator uncertainties includingmisalignments during installation or due to aging and wearing out of the mechanical andelectrical parts in practical operations increase the complexity and difficulty further. In thisdissertation, attitude control demand is investigated for the over-actuated rigid spacecraftsystem in present of parameter uncertainties and external disturbance as virtual control firstly,then the focus is the control allocation design to achieve some better performances even theactuator uncertainties are considered.For spacecraft attitude stabilization system with redundant reaction flywheels, an robustadaptive control law based on backstepping method is firstly developed as a virtual controldemand considering disturbances and parametric uncertainties. Further, a method for dynamiccontrol allocation is also investigated which enables optimal control distribution among theactuators to be designed. One advantage of the control allocation is that even though theactuator constraints and sensor noises or undesired signals are considered, improving thesmoothness and stabilization of the control torques.Further for attitude stabilization issues of a rigid spacecraft in present of uncertaintiesthat is actuators misalignment, an adaptive backstepping based sliding mode control algorithmhas been developed. Lyapunov stability analysis shows that the attitude and angular velocityconverge to zero. Moreover, an novel updating law is employed for the implement of attitudecontrol law as well, in which the possible singularity problem caused by the estimate ofuncertainties due to actuator misalignment is solved. In addition, using the estimated values ofthe actuators misalignments, a dynamic control allocation is investigated to distribute thedesired control command among the redundant actuators. This method extends theconventional quadratic programming control allocation by penalizing the previous step beforesampling intervals and minimizing the system energy consumption.Finally, numerical simulation examples for spacecraft attitude control system is involvedto illustrate the effectiveness and feasibility using the proposed control scheme.