Fixed-time Attitude Tracking for Flexible Spacecraft with Actuator Constraints and Prescribed Performance

This manuscript investigates the issue of attitude tracking for a flexible spacecraft considering parametric uncertainties, environment disturbances, unmeasured flexible vibration and actuator constraints. Firstly, a novel performance function with fixed-time convergence property is defined to achieve the desired attitude tracking performance and the maximum convergence time is able to be perselected. Then, a tracking differentiator is adopted to solve the issue of repeated differentiations in the traditional backstepping control process. In addition, the requirements to know the system parameters, and the upper limit of the lumped disturbance torque in advance have been eliminated by adaptive updating technique. Furthermore, the actuator constraints are solved by designing a new auxiliary system to counter the adverse effects. Finally, the simulation analysis is conducted to validate the effectiveness of the designed control scheme.