Abstract: To satisfy the requirement on low-power magnetic bearings of magnetically-suspended-flywheel (MSFW) with flat rotor applied in spacecraft, a class of radial permanent-magnet-biased magnetic bearing (RPMB), named thimble-RPMB, is presented. It is homopolar, so it has low rotational loss. Its poles have short axial length and flexible pole-arrangement, because its working gaps distribute along two concentric circles in only one layer, and radial magnetic forces are concurrent in one plane. According to different requirements of completely-active MSFW and 2-axis-active MSFW, 3 species of thimble-RPMB are analyzed and designed, namely, pole-aligned, pole-interlaced and pole-biased, by the equivalent-magnetic-circuit method and FEA simulation. The designed completely-active MSFW has short axial length, light weight, and high precision. The optimally designed 2-axis-active MSFW has high passive stiffness, high current stiffness, and high stability of current stiffness.

Key words: Fault tolerance, Magnetic field decoupling, Magnetically suspended flywheels, Permanent magnet biased magnetic bearings, Stiffness