Test characterization of infrared phototransistors-based sensors for close-proximity operations

On-orbit servicing and on-orbit assembly represent very appealing mission concepts that could facilitate the exploitation of the space environment. Autonomy is a critical requirement for systems aimed at the execution of these operations. The development of enabling technologies for this type of missions is a focal research topic for the global space community. The AUTOMA project (University of Padua, Italy) aims at the development of technologies to enable the on-orbit assembly of a standardized modular unit by means of a robotic arm. The goal is the development of a capture interface, composed of a gripper mechanism and a suite of close-range navigation sensors (a navcam, four time-of-flight sensors, two custom matrix sensors based on a set of phototransistors), and the mock-up of a modular assembly unit. The paper prevalently focuses on the conspicuous series of tests that has been performed at subsystem level for the characterization of the two custom matrix sensors, both in terms of their resolution and range of application. In particular, the test campaign has proven how the in-plane matrix sensor provides information about lateral misalignment and relative distance with a resolution of a few millimetres while the roll matrix sensor provides information about the angular roll misalignment with a resolution dependent on the distance between the two bodies. In addition, an analytical relation for the computation of the relative distance through the information provided by the in-plane matrix has been investigated.