Research On Attitude Control For Reusable Launch Vehicles Based On Adaptive Fuzzy Strategy

In recent decades,reusable launch vehicles(RLV)came into being in order to reduce the operational cost of access to space for human,while improving the efficiency of space transportation and conducting space research.As a new type of multi-purpose aircraft,a RLV has many advantages in reusability,low cost,high security and so on,which has become the research focus across many countries.However,a RLV has many characteristics such as great angle of attack,wide range of flight envelope and complicated aerodynamic characteristics in the process of reentry flight.Hence it is critical to study the dynamic model and control system of RLV during reentry phase.The reusable launch vehicle is considered as the research object in this paper and the model characteristics of RLV during reentry flight phase are analyzed.Most importantly,the attitude control strategy for RLV is developed,and the main contents are provided as follows:Ignoring the influence of the Earth's rotation on the aircraft in the reentry flight process,the aerodynamic force and moment model and six-degree-of-freedom(6-DoF)dynamic model of the reusable launch vehicle are established.Since the airborne states and flight conditions of the RLV vary dramatically during reentry phase,the aircraft is subject to the parameter uncertainties and the external disturbances.Then on the basis of the 6-DoF dynamic model of reentry RLV,the control-oriented model is further obtained.Considering the high nonlinearity and multi-variable coupling characteristic of RLV model and the influence of parameter uncertainties and external disturbances,an adaptive fuzzy attitude control strategy based on compensation controller is proposed.The parameter uncertainties and external disturbances are regarded as a system uncertainty term,and the fuzzy logic system combined with adaptive technique is used to approximate this term online.To reduce the influence of the modeling error of fuzzy system on the control performance of the vehicle,a compensation controller is introduced to improve the attitude tracking performance for reentry RLV.Besides,the stability of closed-loop control system is analyzed based on the Lyapunov theory framework.Finally,the simulation results show that the proposed control strategy can achieve stable attitude tracking for reentry RLV.In addition,an attitude control strategy using adaptive fuzzy H_?is proposed in view of the advantage of H_?control with proper handling of external disturbances.The adaptive fuzzy control system is used to approximate the model uncertainties and the term of H_?control is designed to improve the robustness of the control system.Meanwhile,to avoid the weakening problem of approximation property of fuzzy system caused by the introduction of H_?control term,the attitude tracking controller is developed based on the adaptive fuzzy H_?control to ensure the tracking performance of the vehicle within the fuzzy approximation region of attitude angle,while the attitude stabilization controller is designed to ensure the stability of the aircraft by combining the boundary adaptive law outside the fuzzy approximation region of attitude angle.Within the framework of Lyapunov theory,the stability analysis of the closed-loop system is carried on.Furthermore,the simulation analysis verifies the effectiveness and the robustness of the proposed control strategy.