Fast Path Planning And Longitudinal Guidance Of Hypersonic Reentry Vehicles With Multiple Constraints

Hypersonic vehicle(HFV)has become the development direction of new missile weapon research because of its extremely high Mach number,which can greatly cut down the reaction time for the enemy to take countermeasures on the battlefield,thus weaken the effectiveness of the existing defense systems.Trajectory planning as well as guidance is the core of the HFV overall design and the key to the success of reentry flight.In the control system design,the complexity involving high Mach number and long range flight should be paid much attention.Besides,some practical constraints such as monitoring areas and no-fly zones increase new difficulties for the path planning and tracking control.Therefore,the study of path planning and guidance for hypersonic reentry vehicles with multiple complex constraints is of practical significance.Taking a hypersonic reentry vehicle as the research object,this thesis starts from analyzing the multi-constraint conditions by modelling them in proper functions of related variables.Focusing on fast path planning and guidance of hypersonic reentry vehicles with multiple constraints,the main contents are as follows:First,a segmented trajectory optimization strategy based on the Gauss pseudospetral method(GPM)is proposed for hypersonic vehicles in reentry process where some monitoring and no-fly zones are involved.The segmentation of the trajectory converts the original optimal control problem of the trajectory optimization into multiple segment optimal control problems.Then with the help of GPM,the trajectory of each segment is discretized,and the continuous multi-segment optimal control problem is transformed into a non-linear programming problem(NLP).In the meanwhile,considering the requirements of high computing efficiency and the engineering practicability comprehensively,we put forward a weighted performance index of reentry time,path-and-heading-angle related variables.The proposed performance index and corresponding optimization strategies definitely provide us the rapidity of path planning,the smoothness of flight trajectory,the flatness of controlled variables,and the improvement of computational efficiency.Second,the proportional-integral-differential(PID)method,which is widely used in engineering,is employed to design the guidance law and control law based on the reference ground track(RGT).In the longitudinal nominal trajectory of HFV,the feature points are selected according to height,Mach number,angle of attack and pitch angle.According to the definition of" instantaneous"equilibrium,the system is balanced and linearized at the feature points.The nonlinear tracking problem is transformed into a linear time-invariant stability problem(LTI),and the closed-loop system is stabilized along the traj ectory through the linear time-invariant stability theory.The gain of each channel of the guidance loop designed under the linearized system is obtained,and then the original nonlinear system is controlled.The elevator is used as the output of the controller and the input of the system.Finally,the longitudinal guidance of reentry trajectory is successfully realized.