Electromagnetic compatibility problems of ELSA — Novel component for spacecraft attitude control system based on concept of spherical actuator

The most common technique for satellite attitude control assumes the use of rotating mechanical parts on-board. Traditionally such a system consists of one to four Reaction Wheels or Control Moment Gyroscopes. Control of the satellite orientation can be done by acceleration of the proper wheel around its axis of rotation. The attitude of the satellite changes according to the conservation of angular momentum law if acceleration of the appropriate wheel appears. As a potential alternative to the use of set of Reaction Wheels, a single Reaction Sphere held in position by magnetic levitation has been proposed. Authors of this paper are currently involved in the development of a new type of spherical actuator, which consists of a20-pole stator and an 8-pole permanent magnet hollow iron-core rotor. A reaction sphere laboratory prototype has been built and tested. Currently, a second generation of this type of device is under development. While functional problems related to this type of system start to be understandable and clear, there are still several problems to be solved before a possible use of this actuator on-board of a spacecraft. One of such problem is related to strong magnetic fields outside of the system. In this article we present models developed for ELSA reaction sphere system. Then we presents results of analytical and numerical modeling of electromagnetic noise outside of the sphere system taking into account different shielding solutions and modes of operation. The task is not trivial taking into account that shielding material has a strong impact on a system behavior and properties including generation of `sticking forces' which can block the rotor. Finally, a comparison of results with typical requirements for spacecraft subsystems is performed.