Research On Fixed-time Attitude Tracking Control For Reusable Launch Vehicle

As a new aerospace vehicle,reusable launch vehicle(RLV)has been developed widely for its significant value in both military and civil use.However,due to its characteristic of large-space and multiple velocity field,RLV exhibits high nonlinearity and strong coupling characteristics.In addition,model uncertainties,external disturbance and wind disturbance makes reentry attitude control a great challenging research subject.In order to realize the safe and stable reentry flight of reusable launch vehicle,this dissertation discuss the reentry attitude control problem based on the theory of fixed-time convergence control.Firstly,the attitude tracking control scheme for reusable launch vehicle is investigated based on the non-singular terminal sliding mode.Taking the attitude angle tracking errors and its derivatives as new state variables,the attitude control model is simplified into a second-order system.A novel nonsingular fixed-time terminal sliding mode controller is presented to guarantee that the attitude tracking error converges to zero in a fixed-time.Secondly,the comprehensive design of uniform robust exact disturbance observer and fixed-time controller for reusable launch vehicle is investigated.A uniform robust exact disturbance observer is designed to accurately estimate the disturbance with a bounded convergence time.Based on the disturbance estimation,a nonsingular terminal sliding mode controller is designed to ensure that the guidance command can be tracked within a fixed-time.Furthermore,the stability of the closed-loop system under the control scheme is derived using Lyapunov technique.Thirdly,the attitude control problem of reusable launch vehicle is investigated based on multivariable super-twisting fixed-time comprehensive control strategy.According to the multiple time scale principle,the dynamics of attitude motion are divided into attitude angle subsystem and attitude angle rate subsystem: based on multivariable super-twisting fixed-time approach,comprehensive design of fixed-time disturbance observer and controller is proposed to ensure the attitude angle tracking error converges to zero within a fixed-time.Finally,a fast nonsingular fixed-time terminal sliding mode control strategy is proposed for the attitude control of large lift-drag ratio reentry vehicle with wind disturbance.A six-degree-of-freedom model with wind disturbance is established.The wind disturbance is introduced into the attitude control model of reentry vehicle in the wind speed variations form.A fixed-time controller is designed to ensure that the guidance command can be tracked within a fixed-time under model uncertainties,external torque disturbance and wind disturbance.