Stereo-Vision Based 3D Modeling of Space Structures

Servicing satellites in space requires accurate and reliable 3D information. Such information can be used to create virtual models of space structures for inspection (geometry, surface flaws, and deployment of appendages), estimation of relative position and orientation of a target spacecraft during autonomous docking or satellite capture, replacement of serviceable modules, detection of unexpected objects and collisions. Existing space vision systems rely on assumptions to achieve the necessary performance and reliability. Future missions will require vision systems that can operate without visual targets and under less restricted operational conditions towards full autonomy. Our vision system uses stereo cameras with a pattern projector and software to obtain reliable and accurate 3D information. It can process images from cameras mounted on a robotic arm end-effector on a space structure or a spacecraft. Image sequences can be acquired during relative camera motion, during fly-around of a spacecraft or motion of the arm. The system recovers the relative camera motion from the image sequence automatically without using spacecraft or arm telemetry. The 3D data computed can then be integrated to generate a calibrated photo-realistic 3D model of the space structure. Feature-based and shape-based approaches for camera motion estimation have been developed and compared. Imaging effects on specular surfaces are introduced by space materials and illumination. With a pattern projector and redundant stereo cameras, the robustness and accuracy of stereo matching are improved as inconsistent 3D points are discarded. Experiments in our space vision facility show promising results and photo-realistic 3D models of scaled satellite replicas are created.