Disturbance-Observer-Based Robust Backstepping Attitude Stabilization of Spacecraft under Input Saturation and Measurement Uncertainty

The problem of control input saturation and measurement uncertainties in spacecraft attitude control systems is investigated in this paper. Asymmetric limitation of the control torque and additive attitude measurement errors are considered in the backstepping attitude controller design. Stable antiwindup compensator is employed to handle the adverse effect of input saturation. The additive attitude measurement errors, external disturbances, and parametric uncertainties are compensated by the outputs of stable nonlinear disturbance observers in the robust controller design. The tuning conditions of controller parameters are derived based on the Lyapunov analysis, and it is proved that attitude, angular velocity, saturation compensator states, and disturbance observer states converge to small neighborhoods of zero. Simulation results illustrate the effectiveness of the proposed control approach.