Nonsingular robust geometric attitude control based on fictitious tracking state

The attitude tracking control problem of rigid spacecraft is addressed in this work with external disturbances, parameter uncertainties, and input saturation. A novel nonsingular robust geometric control method is presented, which leverages the advantages of the exact linearization method, active disturbances rejection control (ADRC), and a novel fictitious tracking state technique. Firstly, the global exact linearization of the system is achieved with the aid of the exact linearization method so that the complicated nonlinear system is simplified as a linearized form. Then, ADRC is combined with the linearized system to guarantee its tracking performance and robustness against uncertainties. Furthermore, a serious singularity problem existing in the linearization procedure is pointed out and analyzed, and the novel fictitious tracking state technique is first proposed to avoid the singularity problem and satisfy the input saturation constraint. Finally, some numerical simulations are organized to verify the effectiveness of the proposed method.