Cryogenic magnetic bearing

Magnetic suspension provides an alternative to rolling-element bearings for some precision gimbal applications. The Cryogenic Magnetic Bearing program includes studies of magnetic suspension for a gimbal bearing requiring long life (greater than 7 years); low runout (less than 5 microrads bore-sight error due to runout); and low, uniform drag torque. Additionally, the bearing is to operate is an oscillating mode, from room-ambient (300 deg K) to liquid nitrogen (77 deg K) temperatures at ambient pressure and in a hard vacuum (10 (exp-6) torr). Two magnetic suspension alternatives were studied: an all-active approach using electromagnets to control all five bearing degrees-of-freedom and a Passive-Radial Active-Axial (PRAA) approach using passive magnetics to stabilize four of the five bearing degrees-of-freedom and an electromagnet to control the fifth. The all-active approach provides a lower weight, better- accuracy bearing system than the PRAA system, but requires more quiescent operating power and is electrically more complex. The PRAA was selected for hardware study to produce a simple, low-power magnetic system.