Development of a Multi-Axial Force Sensor for Small Satellite Docking

In light of a growing interest in the on-orbit servicing of small satellites, docking systems are becoming increasingly important. Particularly for low-mass satellites, the knowledge of the loads exchanged during docking is critical not only for the docking interfaces but also for the attitude control systems. Hence, the addition of load measurement capabilities to the ground testing facilities becomes valuable. For this reason, a multi-axial force sensor (MAFS) tailored for the characterization of small satellite docking systems has been developed. The MAFS employs four single-point load cells enabling load measurements along two orthogonal axes. Eventually, the MAFS was integrated into a laboratory facility and utilized in docking tests. Positioned at the periphery of a low-friction table, the mockup of a satellite, equipped with a probe, freely moves over the table supported by three gas cushions. The docking event occurs as the probe impacts the drogue, which is mounted on the MAFS. The acquisition of docking loads exchanged between the probe-drogue surfaces is enabled by the MAFS. The frequency response of an impulsive load has been used to determine the first natural frequency of the MAFS. The resulting frequency was then compared with the results of a numerical normal mode analysis to evaluate further improvements to the structure. The accuracy of the dynamic measurements has been estimated employing the impulse-momentum theorem. The impulse was derived from the MAFS force measurements, while the momen-tm was derived from the positional data provided by a motion capture system. The overall relative error was 3.1%.