Research On Trajectory Planning And Control Method For Spacecraft Landing On Small Body

Small body landing detection is usually an important part of deep space exploration.Spacecraft’s autonomous navigation,guidance and control is one of the key technologies to soft landing.In this thesis,the predictive guidance and robust control of irregular small body landing is researched considering the characteristics of dynamic environment nearby small body,for the convex optimization problem for landing trajectories,landing trajectory determination and tracking control.The main contents of this paper are as follows:Firstly,the dynamic model of small body landing is established and the guidance and control scheme is designed.Aiming at the characteristics of irregular gravitational field of small body,methods of the spherical harmonic function model,polyhedron model and mascon model are introduced.Then,the orbit dynamic model of small body landing is established.Considering the characteristics of landing on irregular small body,designing a soft landing mission and proposing the entire guidance and control algorithm structure.Secondly,the method of trajectory planning based on convex optimization with multiple constraints is researched.Analyzed the constraints of landing on irregular small body,for the reason of collision avoidance between the detector and small body,designed a landing trajectory planning method combined with circumnavigation phase and vertical landing phase.An optimal separating hyperplane constraint is imposed during the circumnavigation phase that ensures spacecraft will not collide with the surface of the asteroid.Planned the landing trajectory of circumnavigation phase and vertical landing phase.Thirdly,the method of determining the landing trajectory considering of error compensation.An optical navigation observation model is established,And multiple sight measurement is used for determining the position and velocity of the detector.Navigation filter is designed based on Extended Kalman Filtering.Base on this,considering the impact of unmeasured disturbances or omitted modeling information in a complex environment of small bodies,input observer is researched in order to improve navigation accuracy.Finally,the method of trajectory tracking predictive control in uncertain environment is researched.As to the impact of external disturbances during soft landing,the method of tracking prediction control algorithm based on quadratic programming is designed.Considering detector state constraints and fuel limits,combined with Multi-step prediction and tracking feedback control structure state quantity,realized tracking control of planning trajectory.