An attitude control algorithm for reusable launch vehicle(RLV) in reentry phase is proposed based on sliding mode variable structure control technique.The aerodynamic characteristics of RLV vary rapidly,and the serious uncertainties and nonlinearities exist in the reentry flight phase.As an example,American X-34 technology demonstrator is investigated.The chattering brought by the variable structure control technique is eliminated efficiently by choosing a suitable reaching law and a sign function.A control mode of reaction control system is presented based on the RCS scheme of X-34 vehicle.As two different attitude control effectors,aerosurfaces and RCS,are employed in the reentry flight phase,a composite control strategy based on the dynamic pressure variety is presented.Also,an actuator model and a RCS thruster model are built.Analysis and nonlinear simulation results show that the sliding mode variable structure controller achieves better performance,the overshoot and steady-state error are only 0.7% and 0.04° respectively.
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