A Systematic Output Redefinition for Nonlinear Attitude Control of a Flexible Spacecraft

In this paper, a novel output redefinition is presented for attitude control of a flexible spacecraft. Attitude maneuvers induce undesirable vibration in the flexible appendages which degrades attitude control system performance. The attitude pointing and stabilization requirements of today advance space missions show the undesirable vibration suppression importance. If the flexible appendage tip-point is selected as the system output, the system model is nonminimum phase. The output redefinition method is an effective method to make the model minimum phase. By a deeper insight about the output redefinition method, a novel systematic method is presented such that the attitude control system performance is modified. Then, a nonlinear H∞ attitude control method is desined based on the redefined model system. For the situation that modal variable are not measurable, a modal observer is presented. The simulation results verify the presented method effectiveness in a flexible spacecraft attitude control problem in presence of mode uncertainties and unknown disturbance.