Automatic spacecraft docking using computer vision-based guidance and control techniques

An innovative approach to automatic spacecraft docking using a computer vision-based control system is introduced. Precision control of the relative spacecraft velocity is required to achieve 'soft' docking with a docking platform on a space station or an another spacecraft. We propose use of a computer vision system as a position and orientation sensor for obtaining feedback information used by guidance and control loops. A camera, fixed to the spacecraft, tracks a standard rhombus mark fixed on the docking platform. Discrete-time position and orientation estimates of the spacecraft, relative to a coordinate frame fixed to the docking platform, are obtained by solving a constrained nonlinear least-squares problem and are used by the spacecraft feedback control loops. The accuracy of the computer vision estimates improves as the relative range decreases, thereby providing improved feedback information when it is most critical. Feedback control loops for the spacecraft, using three pairs of gas jet thrusters, are suggested that keep the camera always pointed at the rhombus mark and that perform precise control of the spacecraft range to achieve soft docking. The interactions between the vision system and the control systems are emphasized. Computer simulations of an integrated docking system verify the practical feasibility of this proposed automatic docking approach.