Research On Trajectory Optimization,Guidance Method For Small Body Landing Exploration

Landing exploration is the major part of the future deep space exploration missions.Trajectory optimization and guidance algorithms are the key techniques for a safe and precision exploration mission.Considering the influence of the complex constraints and the uncertain dynamic environments,this dissertation conducted a deep research on the trajectory optimization and guidance algorithm for the small body landing exploration to improve the computational efficiency and control accuracy with support of the 973 program ‘Research on navigation,guidance and control for planetary landing'.The main contents are organized as follows.Firstly,the dynamic equations for small body landing and surface motion are derived.The motion trajectories under different terrain parameters are researched.The analysis expressions of gravity potential function and its first and second partial derivatives of three-axes homogeneous ellipsoid model,polyhedron gravity model and interior sphere harmonic gravity field model are given,respectively.Secondly,the landing trajectory optimization methods for multi-constraints on small bodise are researched.First order necessary condition of the optimal solution is derived based on the Pontryagin's maximum principle.A state transfer matrix based algorithm is adopted to compute the Jaccobi matrix and this improves the optimization accuracy.A slack variable is introduced to convert the non-convex constraint to a convex constraint.The original fuel-optimal trajectory optimization problem is solved through a sequence solving procedure of second-order cone programming(SOCP)problem.Nextly,the guidance algorithms for small body landing under uncertain conditions are researched.The polynomial chaos is introduced to describe the uncertain propagation.The thrusts obtained by this robust trajectory optimization algorithm can avoid the final states of the trajectory divergence excessively.A novel active trajectory control-based intelligent landing strategy is also proposed in order to reduce the potential danger of the landing on small bodies caused by unexpected bouncing.Then,hopping trajectory optimization and guidance algorithm in weak gravity environment are reached.The movement mechanism of surface motion on small bodies is first analyzed.The surface escape velocity is computed and the motion trajectory around the relative equilibria points is discussed.A multiple constranits fuel-optimal trajectory planning problem is constructed and be solved by convex optimization method.The influence of the transfer distance to the control precision is also analyzed.Considering the uncertain environment on the surface environment of small bodies,a multiple sliding technique is adopted for the design of guidance law.This guidance law is robust against unmodeled yet bounded perturbations and is demonstrated to be very accurate and flexible for the surface motion on small bodies.Finally,a semi-physical simulation system for small body-landing trajectory planning and guidance is constructed.Meanwhile,the proposed guidance algorithm is certificated through this semi-physical simulation system.The dynamic environment around the small body is simulated through a smooth platform and air suspension system.The onboard computer is PC104.The navigation sensors include the optical camera,laser range and inertial measurement unit.The propulsion system are nozzle and flywheel.A software for human-computer interaction is also designed to demonstrate the experimental results and store the test data.