Disturbance observer based H∞ control for flexible spacecraft with time-varying input delay

In this paper, a composite disturbance-observer-based control (DOBC) and H∞ control scheme is applied to solve the spacecraft attitude control with time-varying input delay. Compared with some existing results, distinct features of the proposed method are that the delay-dependent disturbance observer and H∞ controller are used to estimate and compensate the main disturbance caused by flexible appendages and to attenuate exogenous bounded disturbances with attenuation level, respectively. The proposed design is obtained by combining the augmented Lyapunov functional with linear matrix inequality technique. The effectiveness of the proposed design method is illustrated via a numerical example.