A Magnetically Suspended Large Momentum Wheel

An 800-ft-lb-sec engineering prototype momentum wheel assembly was designed and fabricated, in which a 64-lb rotor was suspended on radial-passive, axial-active magnetic bearings and rotated at 10,000 rpm. The rationale for the selection of the magnetic bearing configuration, control concepts for the active axis, and the compensation for structural interactions are discussed. Measurements of bearing stiffness and damping, drag torque, and wheel performance are presented. Testing has confirmed that low-drag, unlubricated, wear-free operation can be attained while satisfying functional spacecraft requirements. It was determined that failure of an electronic component could be safely negotiated on the touchdown ball bearings, with a redundant electronics channel being activated to restore suspension. The structural integrity of the unit was confirmed through exposure to sinusoidal vibration and launch-level random vibration. In terms of weight and power dissipation, magnetically suspended momentum wheels compare favorably with conventional wheels, and considerable weight saving may be realized if a "no single point failure' requirement exists. It is concluded that magnetic bearings are capable of providing reliable, long-life operation in momentum wheels and other spacecraft applications.