The Space Debris population has grown rapidly over the last few decades with the consequent growth of impact risk between current objects in orbit. Active Debris Removal (ADR) has been recommended to be put into practice by several National Agencies in order to remove objects that pose the biggest risk for the space community. Current ADR methods can be divided into contact and contactless methods for complete removal. Those methods that require physical contact with the target have applicability limitations depending on the rotational motion of the target. Therefore, a de-tumbling phase prior to the capturing phase may be necessary.

My research at Southampton University (UK) focuses on the analysis of eddy currents on space debris objects and its application for de-tumbling processes. Within this talk, I will present my research project in the frame of the Stardust program and the work planned for my secondment at DFKI.

Given the fact that most space debris objects contain a large amount of conductive materials, it is possible to generate eddy currents. This offers the possibility to decrease the rotational rates of the target without any mechanical contact. The eddy currents phenomenon is a dissipative effect based on the transformation of kinetic energy into heat due to Joule’s law. This process may be done actively by a chaser spacecraft with a magnetic coil on-board based on high temperature superconducting wires. This design allows placing the chaser spacecraft several meters away from the target object. 

Moreover, the magnetic interactions between the two objects generate forces and torques on both spacecraft which need to be counteracted on the chaser spacecraft. The AOCS/GNC subsystem needs to guarantee that the magnetic coil is always pointing in the appropriate direction with respect to the target object and that the relative distance is constant. Therefore, specific sensors are needed to measure the angular rates of the target (up to 50-60 deg/sec), relative distance throughout the process (of the order of few meters w.r.t to the surface of the target) and relative attitude of the chaser w.r.t. the target. The de-tumbling process can last for several days/weeks and the chaser may need to be placed at two relative positions to damp all the angular components. Therefore, the illumination conditions may not be optimal for the sensors at specific moments of time. Furthermore, any delays in the processing of the data and operation of the actuators will affect the control of the chaser and need to be studied.

The main objectives of my secondment at DFKI are to identify and understand the most appropriate sensors and sensor data processing algorithms for this process, continue the development of the GNC subsystem using MARS/Adams and carry out tests in the INVERITAS facility.