Research On Reentry Guidance Method Based On Predictive Control For Hypersonic Vehicles

Hypersonic vehicles have the characteristic in high flight speed,strong defense penetration,and large flight range,as well as the good prospects in military and civilian aspects.Therefore,hypersonic technology has been developed rapidly in recent years,and become the focus of the research gradually.The reentry guidance algorithm as a key of hypersonic technology has also been concerned widely.While the vehicle entry the reentry phase,the severe change of flight environment result in the changed on the initial conditions.Also,under the influenced of environment aspects in the actual flight process,the original flight trajectory should be changed.According to these causes,it is necessary to design the reentry guidance method online.Aiming at the reentry trajectory optimization problem for hypersonic vehicles,this dissertation expands the following research in three areas:The article does the research based on the reference-trajectory guidance.Firstly,it is necessary to generate expected trajectory.Based on the flight objective,the flight model,and the constrained conditions,the optimal control problem has been established.Then the optimal trajectory is obtained according to the Gauss pseudospectral method.The process of tracking this expected trajectory is proposed in the next.Then in the process of tracking the trajectory,propose the predictive control method to improve the robustness of the vehicle.The optimal control problem has been established based on the predictive control.The receding optimize method is proposed to predict the flight trajectory based on the actual flight state.At last,the original problem is transformed into a nonlinear multi-objective programming by using the Gauss pseudospectral method.And then the actual flight trajectory state variable and controlled variable is calculated by the optimized method.The effectiveness and advantage of the proposed method to tracking the expected trajectory are verified by simulation.It is inaccuracy to tracking trajectory according to the unsmooth problem.Aiming at this condition,this chapter will introduce the curvature to expression the unsmooth degree of the problem.Also design the changed predictive horizon strategy according to the curvature.Initially,set the judged points between the adjacent Gauss point on the expected trajectory.And then calculate the comprehensive weightingcurvature of height,velocity,flight path angle and angle of attack on these points.After that it takes to comparing the curvature with the standard value.That means the curvature should be the criteria to set the length of the predictive horizon.Finally,determine the length of the predictive horizon in the current guidance period.The optimal control problem is established based on the changed predictive horizon of predictive control.Finally,the Gauss pseudospectral method is used to solve the control problem.The effectiveness of the proposed method compared to previous reentry guidance method to tracking the expected trajectory are verified by simulation.