Return Guidance And Control Methods Of Vertical Takeoff Vertical Landing Reusable Launch Vehicle

Reusable launch vehicles(RLVs)are the main mean of fast and low-cost shuttle to and from space in the future.Among RLVs based on different takeoff and landing schemes,vertical takeoff vertical landing(VTVL)-RLVs are currently hot direction because it VTVL-RLVs have the advantages of small workload for improvement based on traditional rocket configuration,low landing site demand,relatively low technology difficulty as well as research and development cost.Due to the large airspace and speed range,strong internal and external disturbances and uncertainties,complex and changeable flight environment and different actuators switching in different flight phases in return process of VTVL-RLV,it is a major challenge to design feasible guidance and control methods of VTVL-RLV for realizing the controlled recovery of VTVL-RLV.Considering the different characteristics of each flight phase and actuators in the phase in return process of VTVL-RLV,the return guidance and control methods of VTVL-RLV are studied by using optimal control methods and nonlinear control methods in this dissertation.Specific research contents include:Firstly,the first stage of VTVL-RLV movement mathematical model in return process is established on the basis of the analysis of the actuator of the first stage of VTVL-RLV.After that,the reference return process trajectory of the first stage of VTVL-RLV is given according to the characteristics of the trajectory profile.Secondly,to solve the problem of high-precision exo-atmospheric guidance for boost-back burn phase of VTVL-RLV,geometry and time updaters-based arbitrary-yaw iterative guidance for reusable rockets is presented.In order to deal with the possible large deviation due to the separation of rocket stages and the transverse deviation introduced by earth rotation,the arbitrary-yaw iterative guidance is formulated by using optimal control method via the abandonment of small yaw angle hypothesis.On this basis,a double-deck target-updating algorithm is proposed.On the one hand,a geometry-updater is developed based on the geometry relationship of elliptical orbit for the compensation of guidance errors originated from ignored terminal position constraints in the guidance.On the other hand,based on the estimated remaining time,a time-updater is designed to update the terminal states in inertial space for the compensation of the moving of guidance target in inertial space due to earth rotation.The simulation results show that the high-precision exo-atmospheric guidance requirements for boost-back burn phase of VTVL-RLV can be satisfied with the presented method.Thirdly,for the multi-constraint endo-atmospheric guidance requirements of VTVL-RLV,the guidance methods of aerodynamic guidance phase and vertical landing phase are studied respectively.The contents of this part consist of two levels:(1)To solve the problem of angle-constrained guidance in aerodynamic guidance phase,the relative kinematics model between VTVL-RLV and the virtual target and the state equation of the guidance system are established at first.Whereafter,a second-order bi-limit-weighted homogeneous fixed-time convergent disturbance observer(FxTDO)is given,and then FxTDO-based nonsingular fast terminal sliding mode guidance(FxTDOB-NFTSMG)with impact angle constraint based on the presented FxTDO is designed by using disturbance observer-based control(DOBC)method to compensate the disturbance effects and reduce the chattering problem because of the FxTDO-based compensation.The theoretical analysis and simulation results show that,the FxTDO can estimate the disturbance quickly and accurately without the boundary of disturbance,and VTVL-RLV can reach the preseted target location at the desired impact angle by using the designed guidance method in aerodynamic guidance phase,where VTVL-RLV can reduce the guidance overload requirements at the end of aerodynamic guidance phase due to the method’s finite-time convergence.(2)For the problem of multi-constraint powered landing guidance in vertical landing phase,the classical polynomial method in vacuum is applied to solve the problem of powered vertical landing guidance of VTVL-RLV in atmosphere of the earth.The state equation of the first stage of VTVL-RLV motion in vertical landing phase is established at first,and then the quartic polynomial guidance algorithm is formulated by the optimal control method.The simulation results show that the quartic polynomial guidance algorithm can be applied to solve the guidance problem of vertical landing phase of VTVL-RLV in atmospheric environment.Fourthly,to solve the nonlinear attitude tracking control problem with complex disturbances and large uncertainties in endo-atmospheric descent of VTVL-RLV,the FxTDO-based double-order power fixed-time convergence sliding mode control(FxTDOB-DPFxTSMC)method is presented.The control system model of VTVL-RLV in endo-atmospheric descent is established at first.Then,considering the influence of complex disturbances and uncertainties,the second-order FxTDO given in this dissertation is extended to arbitrary order.In order to reduce the chattering of sliding mode guidance and the deviation of vertical landing guidance caused by control dynamic process and control tracking errors,a double-order power fixed-time convergence sliding mode surface is given by introducing the double-order power correction term with fixed time convergence.Then the FxTDOB-DPFxTSMC is designed based on the FxTDO and the double-order power fixed-time convergence sliding mode surface.The theoretical analysis and simulation results show that,the FxTDO can estimate the state and disturbance of system quickly and accurately,and the tracking control requirements in endo-atmospheric descent of VTVL-RLV can be obtained through the designed control method,where the control accuracy can be guaranteed and the chattering can be reduced by the compensation of FxTDO.Finally,in order to test and verify the comprehensive performance of return guidance and control methods,the 6-DOF simulations of VTVL-RLV in return process are carried out.