Nonlinear attitude control scheme with disturbance observer for flexible spacecrafts

To attenuate the effects of parameter variations and disturbances of flexible spacecrafts on attitude control accuracy and stability, a composite control approach by combining nonlinear disturbance observer (NDO) and feedback linearization (FBL) control is proposed. In this paper, the multiple disturbances that act on spacecrafts from flexible appendages, space environment, and unmodelled dynamics are considered as an 'equivalent' disturbance. The proposed NDO is used to estimate and compensate for the disturbances through feedforward. Stability and tracking performance of the NDO are then analyzed. Moreover, the stability of the FBL+NDO composite control approach is established through the Lyapunov method. Simulation results show that the NDO can estimate disturbances and reduce the effect of disturbances on spacecrafts through feedforward compensation. Robust dynamic performance and attitude control accuracy are effectively improved.