Modular Design and Dynamic Tests on Active Bearing Momentum Wheels

The application of magnetic bearings in space programs requires primarily a reduction in manufacturing cost. This is achieved by a modular concept enabling the manufacturing of wheels of any angular momentum within the range of 30 Nms through 150 Nms. The design of the bearing unit and the reliability concept are described in detail. Finally performance data and test results obtained with a protoqualification model of 50 Nms nominal angular momentum are presented. The preceding Engineering Model was subjected to tests at the DFVLR, on an air bearing platform and to fixed base tests. Dynamic response analysis was utilized in order to find a linear dynamic model describing the dynamics of the wheel and the interaction with the air bearing platform. An overall stability of the open loop system - satellite plus wheel - can be achieved by an appropriate design of the magnetic bearing loops. Closed loop attitude control tests utilizing external vernier gimballing command were required to have tight input rate limitations. The test results show satisfying satellite nutation damping performance.