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A composite disturbance observer and H∞ control scheme for flexible spacecraft with time-varying input delay

This paper considers the attitude control problem of flexible spacecraft with time-varying control input delay. A composite disturbance-observer-based control (DOBC) and H∞ control scheme is applied to control the spacecraft attitude. In the internal loop the disturbance observer estimates and feed forward compensates the main disturbance caused by flexible appendages, while in the external loop different magnitudes of exogenous bounded disturbances with different attenuation levels are attenuated with H∞ controller. The numerical simulation shows that this algorithm can estimate the main disturbance accurately and improve the system's stability effectively.