Safety Guidance And Control For Spacecraft Close Proximity Maneuvers

With the development of space technology,there is a continuous increase of close proximity space mission.Being free from colliding with other space object has been the basic requirement for orbital flying.During the course of close proximity relative motion,short distance and high risk of collision among space vehicles raise higher requirements for the safety of trajectory.Safety flying control technology plays a vital role in close range space mission.This paper adopts spacecraft on-orbit service as research background,space debris and failed spacecraft as the main research targets,and carries out research work aiming at close proximity space application which mainly includes two categories.The first category is formation flying or rapid safety maneuvering;the second category is space debris capture or safe proximity maneuvering of failed spacecraft on-orbit service.By adopting the method of potential field,spacecraft proximity analysis and model description are carried out.Close proximity safety control issues of the spacecraft are solved by designing controllers based on the thought of gradient descent.The main work of this paper includes:Firstly,the analysis and description of close proximity safety issues of the space vehicles are conducted.For convex type spacecraft,the potential field method is employed to describe safe approach issues,and the representation form and characteristics of the potential field function are analyzed systematically.According to the shape and characteristics of the space vehicles,the minimum-volume ellipsoid is adopted for the depiction of the potential field geometrical architecture.Space representation model of close proximity motion of the spacecraft is explored based on core-distance estimation issues of the potential field description.The potential field description models between two rotating rigid spacecraft are established based on the distance estimation between them.By comparing with existing models,the advantages of the potential field models of rotating rigid bodies are pointed out,and the applicability of the models is analyzed.Secondly,research on rapid collision-avoiding spacecraft maneuvering control technology is conducted.Issues concerning safety control during collision-avoiding process are analyzed based on the needs for rapid collision-avoiding maneuvering missions.During this process,there exists a coupling relation between three factors(position,attitude and shape)of serving spacecraft and that of space debris.Based on this coupling relation,collision-avoiding schemes and control strategies are determined.Six degrees of freedom(6DOF)attitude and orbit tracking controller and double repulsive force collision-avoiding controller are designed on the basis of the maximum safety distance principle.6DOF attitude and orbit tracking controller can trace the desired attitude and orbit state;double repulsive force collision-avoiding controller can enhance collision-avoiding performance.By analyzing properties of the controller,the superiority of rapid collision-avoiding maneuvering control method is elaborated.Thirdly,research on safety approach technology of non-cooperative target is conducted.Rotation modes of non-cooperative target are classified,and safety issues are elaborated according to different rotation types.Analysis fouces on safe approach of the non-cooperative target rotating within orbit plane.Based on the double rigid-body potential field model,the description of rigid target approach is conducted by taking the position,attitude and shape of both servicing and target spacecraft into consideration.The rotating potential field is established according to rotating properties of non-cooperative target;and corrected rigid-body repulsive potential field is established according to the characteristics of servicing point approaching the target.The controller which satisfies the requirement of rotating non-cooperative target approach is designed as per conditional constraint of approaching process.Finally,research on safety approach technology of non-convex terminal geometric constraint is executed.Safety approaching issues for non-convex shape target are analyzed aimed at non-convex shape terminal geometric constraint.In order to overcome the problem of local minimum cased by non-convex shape target,harmonic functions are employed to establish the potential filed;and by adjusting harmonic potential field,guidance performance of the potential field is promoted.Based on the description of the potential field of the terminal geometric constraint,safety approaching controller is designed,and the convergence and collision-avoiding properties of the controller are analyzed.By analyzing this collision-avoiding process,the controller can solve the problem of safe fly even under the condition of terminal geometric constraint.This paper deeply analyzes the close proximity safety control issues of space vehicles.Rigid-body potential field description model with certain universality is put forward for convex spacecraft.Research on control method in two types of applications which include rapid collision-avoiding maneuver of space debris and safety approach of non-cooperative target is carried out;for non-convex shape spacecraft,certain terminal geometrical architecture is used for constraint description,and initial exploring work is carried out.The research work of this paper provides an effective analysis method for spacecraft on-orbit flying mission.