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

This study is dedicated to address the predefined-time attitude tracking control problem of spacecraft in the presence of actuator fault, unmeasurable angular velocity, system uncertainties, and external disturbance. Invoking the attitude measurement feedback only, 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 non-singular sliding surface-based predefined-time adaptive controller is synthesized. This controller does not have singularity and is free of chattering. It ensures the attitude tracking error to be stable with predefined-time convergence. The proposed controller's effectiveness is finally verified through numerical examples.