Autonomous Optical Relative Navigation Algorithms For Spacecraft Close-range Rendezvous

Different space activities, such as space transportation, manned space flight, on-orbit servicingand space exploration, have different mission goals. However, they are all related to the determination,change and keep of relative pose between two spacecrafts, and need relative navigation techniqueswith high accuracy. Therefore, the study on relative navigation algorithms has more academic andengineering application value nowadays and in the future. With the mission of cooperative spacecraftclose-range rendezvous as the background, the relative navigation algorithms based on opticalmeasurement are emphatically researched in this paper and the detailed contents are as follows.Firstly, dynamic models of the spacecraft rendezvous and docking in approach phase is given out.Hill equations are chosen as the relative orbit dynamic model, and the rigid-body attitude dynamicsequations are used for attitude kinematics model, which are linearized under the assumption of smallangle.Secondly, relative navigation algorithm for close-range rendezvous is developed based on onlyCCD camera measurement in this paper. The direction vectors from the chaser to the4opticaldiamond-layout feature points could be obtained through CCD measurement. Then, Gaussian LeastSquares Differential Correction (GLSDC) algorithm and Extend Kalman Filter (EKF) algorithm areused respectively to solve the relative position and attitude.The measurement of CCD loses range information, which results in great relative position errorat the initial stage of navigation solution, so it is good to introduce range measurement. The paperpresent a kind of relative navigation algorithm for close-range rendezvous based on integratedmeasurement of CCD and laser range finder. The position from chaser to three non-collinear featurepoints, called range vector, can be constructed from the measurements of optical camera and laserrange finder. Then the relative position and attitude, definded in the target fixed coordinate system,can be directly deduced. EKF algorithm is also used in this method to suppress measurement noises.Besides, because of the high computation burden in image processing, the relative navigationalgorithm based on only optical measurement can merely supply relative position and attitude sparsely,the integrated navigation method for close-range rendezvous is developed based on IMU which hasbetter real time performance and CCD which can compensate the absolute deviation caused by IMU.This method gathers the advantage of both IMU and CCD, and effectively improves the relativenavigation precision and reliability.