A Predefined-Time and Angular Velocity-Free Attitude-Tolerant Control Approach for Spacecraft

This study is dedicated to addressing the predefined-time attitude tracking control problem of spacecraft in the presence of actuator faults, unmeasurable angular velocity, system uncertainties, and external disturbance. Invoking only the attitude measurement feedback, a model-free adaptive state observer is designed to estimate the unmeasurable angular velocity. Its estimation error is governed to be stable with predefined-time convergence. Using this estimation, a continuous and nonsingular sliding-surface-based predefined-time adaptive controller is synthesized. This controller is free from singularities and chattering. It ensures that the attitude tracking error is stable with predefined-time convergence. The effectiveness of the proposed controller is verified through numerical examples.