Adaptive quaternion-based output feedback control for flexible spacecraft attitude tracking with input constraints

This work mainly explores a quaternion-based output feedback control scheme for the flexible spacecraft attitude tracking problem in which not only the unavailability of the body angular velocity measurements is considered, but also external disturbances and uncertain inertia parameters as well as input constraints are explicitly taken into account. The proposed controller incorporates a pseudo velocity filter to account for the unmeasured angular velocity, and the neural network technique is implemented to approximate the system uncertainties of the flexible spacecraft in the synthesis of the control algorithms. It is shown that this developed control method ensures the uniformly ultimate boundedness of the attitude tracking error and the control input can rigorously enforce actuator magnitude constraints. Numerical simulation results are also presented which not only highlight ensuring closed-loop performance benefits from the control law derived here, but also illustrate its robustness in the face of external disturbances when compared with conventional approaches for spacecraft attitude tracking control.