Novel Type of Inertial Actuator for Satellite Attitude Control System Basis on Concept of Reaction Sphere—ELSA Project

Magnetically levitated reaction sphere systems are considered as a new type of actuator dedicated for satellites ACS system. Inertial Attitude Control Systems used in spacecrafts, traditionally consists of one to four reaction wheels (RW) or control moment gyroscopes (CMG). In a principle, the attitude of the satellite can be changed by the reaction to the acceleration of the appropriate wheel. In practice, for optimization, redundancy purposes and ability to three-axis attitude stabilization, four or five wheels are common. Another approach, which states a general base for this work, assumes use of a single reaction sphere which can be accelerated in any direction instead of set of reaction wheels. The sphere can be accelerated in any direction by a three dimensional (3D) motor. Because of its unparalleled symmetry, a hollow sphere delivers constantly a maximum inertia independently of its current rotation axis. A solution investigated here consists in a rotating permanent magnet spherical rotor enclosed in a multi-coil stator. In opposition to conventional ball bearing momentum exchange devices, rotor in this solution levitates magnetically what results in absence of friction and increase of performance. The sphere can be accelerated in any direction by a three dimensional (3D) motor, making the three axes of the spacecraft controllable by just a single device. Furthermore, a hollow sphere has the natural optimal multi axis inertia-to-mass and-volume ratios.