Research On Guidance Algorithm Of Lunar Probe For Soft Landing

Soft landing on the lunar surface is an indispensable part in lunar probing plan.And moreover,navigation,guidance and control are the key techniqu es for lunar soft landing.With the support of Research Center for Deep Space Exploration,Harbin Institute of Technology,"The Study of Lunar Soft Landing High Precision Navigation and Guidance Methods",this dissertation systematically studies guidance problems in the lunar landing procedure employing optimal control,optimization,nonlinear control methods based on precursors' results.To solve the guidance problem of unfixed point soft landing,a fuel-optimal guidance law is developed by Pontryagin maximum principle of the classic optimal control theory.Then,it is proved that the singularity condition that causes control function uncertain can not hold along an optimal trajectory on any closed time interval.In the end,by using nonlinear programming in order to obtain the numerical solution for the optimal trajectory,the two-point boundary value problem is be solved.To solve guidance problems of pinpoint soft landing,a piece-wise constant parametric guidance law is designed by the method of parametric control and control variable parameterization,firstly an optimal open-loop guidance law is designed to obtain the optimal trajectory of powered descent phase of soft landing by using optimal control and optimal parameter selection,and t hen a nominal trajectory guidance method is developed to track the optimal trajectory.Then,the optimal control problem can be transformed into a parameter optimization problem by this method.Hence,the optimal parameters can be solved by the common mathematic programming,and the approximating precision can be enhanced by increasing the number of parameters until an acceptable solution is derived.