Close Relative Navigation For Non-cooperative Spacecraft Based On Stereo Vision

With rapid development of space technology, near Space operations of non-cooperation spacecrafts have become one of future development trends. The confirmation of the relative position and attitude among non-cooperation spacecrafts is a prerequisite for achieving operations such as rendezvous and capture in orbit servicing about non-cooperation spacecraft. As it’s hard for non-cooperation spacecraft to give us its relative position and attitude, so a stereo vision system of non-contact, low-power and cost-effective is usually added for measurement sensor to track star which is used to check its information, in order to obtain the target’s relative parameters. This paper gives a research about algorithm of confirming the non-cooperation spacecraft’s relative position and attitude, expecting for a more practical navigation method with high-precision, real-time and high reliability, as a reference of in orbit operations about non-cooperation spacecraft.In order to ensure the non-cooperation spacecraft can be tracked real-time and precisely, we give a introduction about the measurement principle, then analysis the characteristics of relative position and attitude as well as orbit between track star and non-cooperation spacecraft, establish a set of appropriate coordinates, induce dynamic model of relative position and attitude, and a feasible verification scheme is put forward too.To ensure track star can approach non-cooperation spacecraft, it’s necessary to obtain non-cooperation spacecraft’s relative position and attitude precisely. In this paper, we establish system equations based on relative position and attitude model, as well as observation equations based on stereo vision system, and EKF filter is designed to estimate non-cooperation spacecraft’s relative position and attitude. For lots of derivative operations will be produced while solving Jacobian matrix with EKF in process of estimating relative position and attitude. In this paper we take in account of linear characteristic of relative position model, we design linear state observation for estimating its relative position, and attain to the aim of fast convergence by pole configuration. Moreover, in order to improve the navigation precision and reliability, the method of robust M estimation is taken to eliminate observation error generated while measuring.Considering the requirements of high precision of model and lots of calculation while estimating non-cooperation spacecraft’s attitude with current filter method, The idea of virtual sliding mode is presented in this paper too. A sliding boundary layer adjustable parameters is introduced for discontinuous switching characteristics caused by chattering. Through applying fuzzy logic control in boundary layer, the chattering can be smooth.In order to verify the algorithm of EKF and virtual sliding mode control method both are presented in the paper, a relative navigation semi-physical simulation test platform is built based on stereo vision system, and results are listed.