Observability criterion of angles-only navigation for spacecraft proximity operations

This research studies the angles-only relative navigation problem for spacecraft proximity operations when the camera offset from the vehicle center-of-mass allows for range observability. Emphasis is placed on developing an analytic observability criterion for the camera offset within the context of the Clohessy-Wiltshire (CW) dynamics and evaluating the performance of the navigation algorithm in nonlinear dynamics environment. Further, the newly observability criterion is mathematically derived by changing the analyzing problem of the nonlinear observability into the solving problem of linear equations, and the criterion can be a powerful guideline to be followed to install the camera and execute attitude maneuvers. Moreover, navigation filtering algorithm based on an Unscented Kalman Filter and systematic nonlinear Monte Carlo simulation framework are established to verify the analytic observability criterion and evaluate the performance of the proposed algorithm through typical proximity missions. The sensitivity of the navigation accuracy to spacecraft trajectories and camera offset is presented and discussed. The conclusion is that the camera offset is required to have out-of-plane component and cannot be parallel to the line-of-sight vector in order to supply range observability.