ESA GNC Conference Papers Repository
Electromagnetic position and attitude control for pacman experiment
In-space proximity manoeuvres between small satellites would enable a wide number of operations, among all docking and assembly of large modular structures, as well as spacecraft servicing, refuelling and inspection. Electromagnetic interactions are the simplest solution employed for proximity operations with respect to fuel-based solutions that strongly influence spacecraft operational life. Preliminary studies have been performed mostly on low-friction and low-gravity facilities; in-space demonstrations have been only recently financed by NASA with CPOD and OAAN CubeSat projects. In this framework, PACMAN experiment represents a technology demonstrator whose main goal is to develop and validate in low-gravity conditions an integrated and innovative system for proximity navigation and soft docking based on magnetic interactions. The project has been selected to fly during the 68th ESA Parabolic Flight Campaign, currently scheduled to take place this autumn, within ESA <i>Fly Your Thesis!</i> 2017 programme and supported by the University of Padova. The idea of PACMAN is to actively exploit magnetic interactions for relative position and attitude control during rendezvous and proximity operations between small-scale spacecraft. This will be accomplished by launching a 1U CubeSat mock-up towards a fixed target that generates a static magnetic field; a set of actively-controlled magnetic coils on-board the CubeSat, assisted by dedicated localization sensors, will be used to control its attitude and position relative to the target. This paper will primarily focus on the guidance and navigation control subsystem of the experiment. A closed control loop will be used to power separately the coils into the CubeSat. Relative pose between the CubeSat and the target will be determined by means of a camera vision system and a 6 d.o.f Inertial Measurement Unit (IMU) on board the CubeSat. The closed loop system computes the desired control torques from the position/attitude error information collected by the IMU and the real time image processing. The magnetic forces and torques produced by the magnetic fields interactions will be exploited, assuring the proximity navigation. The inherent self-alignment effect during the free floating phase will assure the accomplishment of the soft docking manoeuvre. The realization of PACMAN experiment will allow to study the attitude of a miniature spacecraft subjected to controlled magnetic interactions in low-gravity conditions and to validate the theoretical/numerical models that describe such interactions. Data collected during the experiment testing will allow to assess the system concept feasibility and its limitations. The proposed technology represents an innovative solution for proximity navigation manoeuvres for small-scale cooperative spacecraft; moreover, tests results will provide precious data that will be exploited to improve the proposed electromagnetic control technology for future in-space missions.