This paper presents the dynamic modeling and fuzzy sliding mode control (FSMC) for a spacecraft with flexible appendages. A first-order approximate model (FOAM) of the flexible spacecraft system is formulated by using Hamilton’s principles and assumed mode method (AMM), taking into account the second-order term of the coupling deformation field. The use of classical Sliding Mode Control (SMC) presents a major problem that appears in the form of chattering. For highly flexible structural models, ideal sliding surface producing pure rigid body motion may not be achievable. In this paper, the discontinuity in the sliding mode controller is smoothened inside a thin boundary layer by using fuzzy logic (FL) techniques so that the chattering phenomenon is effectively reduced. The robustness of SMC only holds in the sliding mode domain (SMD). However, when the amplitude of the actuators is limited, SMD will be restricted to some local domain near zero on the switching surface. Control input saturation is also explicitly considered in the FSMC approach. The new features and advantages of the proposed approach are the use of new dynamic equations of motion of flexible spacecraft systems, and the design of FSMC by taking into account the control input saturation. To study the effectiveness of the corresponding control scheme, the classical SMC case is also developed for the control system. Numerical simulations are performed to show that rotational maneuvers and vibration suppression are accomplished in spite of the presence of disturbance torques, model uncertainty and control saturation nonlinearity.

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