This paper presents a nonlinear control law for large-angle attitude control of spacecraft. For the ROCSAT-3 spacecraft, a highly accurate and robust attitude control is desired during the orbit-raising phase. The three-axis attitude control is achieved using four body-fixed canted thrusters. In the paper, the nonlinear dynamic equations of the satellite are derived and the control requirements are stated. A novel nonlinear attitude control structure is then proposed for spacecraft control problems. The nonlinear controller contains linear feedback terms for stabilization and nonlinear terms for performance enhancement. One salient feature of the proposed approach is that the nonlinear controller parameters are designed using a linear matrix inequality (LMI) method. It turns out the controller design of stabilization and H∞-type performance problems for spacecraft dynamics become rather transparent when the proposed controller structure and LMI method are employed. The design is shown to generalize many existing results. Simulation results based on the ROCSAT-3 system are then presented to demonstrate the proposed design method.
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