Preliminary Analysis of Visual Navigation Performance in Close Formation Flying

Growing interest has been lately put into proximity operations with non-cooperative targets, such as on-orbit servicing and refuelling, which both requires the the system to be completely autonomous. Autonomy is achieved through a robust GNC structure and the navigation system is of primary importance for this purpose. The paper investigates a scenario where a spacecraft (chaser) approaches a target satellite on an elliptical, sun-synchronous orbit. The approach maneuver itself is designed to be both optimal in time/propellant consumption, by means of solution of an inverse optimization problem, and safe, i.e. in such a way that no collision can exist between the chaser and the target. An optical navigation technique which relies both on optical camera and LIDAR measurements would provide the benefits of having more accurate measures and the possibility of assessing the targets shape and status, in case of them being unknown. The measurements' covariance for this navigation systems varies along the maneuver depending on several factors, as the chaser-target line of sight and the target illumination. As navigation and guidance are strictly connected, a change in the measurements' covariance modifies the maneuver's performance and can suggest a complete redesign of the docking. The paper, on the basis of reasonable assumptions for hardware characteristics, provides a preliminary analysis of the relevance of this coupling effect when considering variations in visibility conditions.