Predefined-Time Disturbance Observer-Based Attitude Tracking Control for Spacecraft: A Solution for Arbitrary Disturbances

This article proposes a predefined-time attitude tracking control framework for uncertain spacecraft. By introducing a bounded function, a new predefined-time stability criterion is proposed. Based on the proposed predefined-time criterion, a nonlinear disturbance observer is then developed to reconstruct the system uncertainties and environmental disturbances. The observer is capable of driving the estimation error to the origin within a specific time, even if the initial estimation error is exceedingly large or infinite. The proposed observer does not require the assumption of continuous differentiability or negligible variation of the total uncertainties. Hence, a wide range of disturbances can be handled. Based on the estimated uncertainties, a nonsingular predefined-time sliding mode attitude tracking controller is developed. It is guaranteed that the attitude system is globally predefined-time stable and the attitude trajectory converges to the reference trajectory from anywhere in the state space within a predefined time. The illustrative results using MATLAB/Simulink and real-time simulation via Speedgoat Real-Time Target Machine platform demonstrate the efficacy and performance of the proposed control framework.