Magnetically Suspended Reaction Sphere with One-Axis Hysteresis Drive

We have designed, built and tested a magnetically suspended reaction sphere with one-axis hysteresis drive (1DMSRS) in the Precision Motion Control Lab at MIT. This project is aiming at two goals: (a) exploring the possible design of a magnetically suspended reaction sphere for small spacecraft’s attitude control; and (b) evaluating the performance of a hysteresis motor for the reaction wheel/sphere application. The 1D-MSRS is a motor with spherical rotor, which is magnetically suspended in all translational directions, and is driven by hysteresis motor about vertical axis. For the suspension of the sphere, single dimensional magnetic levitation in vertical direction and bearingless motor around the rotor are combined. An equivalent circuit model of the hysteresis motor is used to analyze the motor’s dynamic behavior. Good agreements between computed and measured motor performance validates the model, which provides a useful simulation tool for further MSRS modeling and control. Test results of the 1D-MSRS show that a starting torque of 8.15 mNm is achieved at 0.7 A zero-peak excitation current, and with this excitation the sphere can run up to 12,000 rpm synchronously in lab with the existence of air drag.