Occlusion Avoidance in Image-Based Control of Multiple Spacecraft

This study develops a novel image-based control scheme to address the on-orbit service mission that multiple spacecraft track a tumbling uncooperative target under a visibility constraint. The chaser spacecraft are commanded to hover above and track stably the feature points attached to the target as well as to avoid the mutual visual occlusion caused by interspacecraft motion. To this end, a new expression of image-based visual servoing dynamics for spacecraft is derived, where the physical meaning of each term is analyzed in detail so that the exact upper bounds of noncooperative terms can be estimated. After that, a novel occlusion description model is established by the projective theory of quadrics. The mathematical elements for describing the imaging elliptic curve and occlusion discrimination function are proposed, whose association with interspacecraft motion is given to guide occlusion avoidance controller design. Combining the artificial potential function with the backstepping control method, a robust control algorithm is designed. The proposed control scheme can achieve the six-degree-of-freedom control objective based on image space, and motion trajectory will not influence others' visibility. Finally, the validity of the control scheme is verified by simulation for a given multispacecraft observation scenario.