Characterization of a new positioning sensor for space capture

Space missions that focus on On-Orbit-Servicing often involve the capture of a target satellite or space debris as a key event in the operational sequence. Space robots are among the most promising technologies to perform this task and mission architectures involving manipulators proved successful in orbit. Such mission scenarios are complex and imply a considerable risk of collision between the chaser and the target vehicles. For the sake of safety, it is of key importance to accurately position the capture interface w.r.t. the gripping point on the target, especially when relative distance is very low. During these phases, the guidance and control algorithms rely on pose measurements provided by navigation sensors that are generally able to reconstruct the target position and orientation only up to a certain distance between the camera and the target. To the purpose of having a complete control of the capture interface until contact, a new sensor based on a LED and a matrix of phototransistors has been developed. This paper describes the sensor and provides its preliminary characterization. A simple theoretical description of the sensor behavior is obtained from geometrical considerations, while experiments have been performed to measure the performances of the actual hardware implementation of the system.