Predictor-Corrector Entry Guidance And Attitude Control For Reusable Launch Vehicle

Reusable launch vehicle(RLV)can be used for space science research,space transportation,and military reconnaissance.In virtue of its rapidity,safty,flexibility and low cost,RLV has a broad developing trend.For the new generation of RLV,The guidance and control system is required to be more robust,reliable and autonomous.The dissertation conducts a research on the entry guidance and attitude control for RLV.Based on the guidance law of shuttle,a predictor-corrector guidance method is proposed in this dissertation.The entry course is divided into two phases,initial phase and glide phase.In the initial phase,the vehicle is guided by a constant bank angle.In the glide phase,a drag acceleration profile is designed through interpolating between upper drag boundary and lower drag boundary.And the corridor of heading angle error is designed for guiding lateral motion.Then the 3-dimension trajectory of the vehicle is predicted by numerical integration.Based on the prediction,the model of angle of attack,bank angle and lateral error corridor is corrected.The PID control law is used to track the drag acceleration profile.Compared with the traditional guidance law,the proposed method is adaptable to the mission with large cross range.The methods based on drag acceleration profile are propitious to deal with the entry constraints.But the attached trajectory-attracking problem is required to be solved.Therefore,the dissertation proposed a predictor-corrector guidance law based on the bank angle model.With the Quasi-Equilibrium Glide Condition(QEGC),the flight constraints are transformed into the constraints on bank angle.The bank angle model is designed as a piecewise-linear function.The sign of bank angle is determined by the reversal time of bank angle.Then the 3-dimension trajectory of the vehicle is predicted,and the angle of attak is regulated to maintain the QEGC.The correction system is based on two fuzzy controllers,which correct the magnitude and reversal time of bank angle,respectively.Considering the longitudinal motion and lateral motion are corrected synergistically,the method is more robust and flexible.With the diversification of entry mission,guidance methods are required to satisfy the constraints of waypoint and no-fly zone.Therefore,the dissertation proposes two guidance methods for the entry problem with no-fly zone and waypoint.The first method plans the flight trajectory on-board based on the relationship between the state of vehicle and the way-piont or no-fly zone.And one bank angle reversal is designed to satisfy those constaints.The lateral error at the way-point and the shortest distance to no-fly zone is calculated based on the predicted trajectory.Then the reversal time is corrected to remove the error.After the reversal,the magnitude of bank angle is corrected to maintain the above guidance result.The second method satisfies the constraints of way-point and no-fly zone based on an optimal reference trajectory.An optimal trajectory is generated by Guss-pseudospectral method.Then some reference points are selected,which partition the entry process into several subsections.A predictor-corrector guidance law is used to make the vehile pass through the reference points rightly in each flight subsection.In the entry process,the attitude motion of the vehicle is nonlinear,high coupled and fast time-varying.The dissertation designs a predictive control law for the vehicle equipped with RCS and aerodynamic surface.Based on the state equations linearized by dynamic inverse method,an analytical optimal predictive control law is deduced.To improve the robustness,the extended states observer(ESO)is introduced to estimate the model error and external disturbance.After the control command is generated,an optimal control allocation method based on PWPF modulator is proposed.The control allocation is obtained by solving the quadratic programming problem.And the PWPF modulator is used to discretize control signal of RCS.The attitude control method has the capacity of disturbance rejection and fault tolerance.Finally,based on the previous chapters,a simulation platform for the 6-freedom entry motion is built.Four entry missions are designed to test the guidance and control method.The research in the dissertation may provide some technical support for the design of Guidance,Navigation & Control(GNC)system and promote the development of the the future RLV.