6.43 There were, however, practical problems with the design. The ES group anticipated that the wheels would wear out both in their axle bearings and their contact surfaces. If the wheels and the tracks they rode in were metal, there would be fretting at their points of contact. These problems could be helped (but no completely eliminated) by lubrication provided special vacuum lubricants were used. There would also be friction losses in the wheels slowing the spin rates of hull and shield. To remedy this, it was suggested that electric motors, coupled to some of the wheels, could provide the same rotational energy to the system as that lost to the friction in the bearings. The ES group also anticipated fatigue problems in the stressed moving parts and their supports. This fatigue, and the unavoidable friction effects mentioned above, would eventually cause failure of some components. Should a wheel jam or break, the first essential step would be to move it away from its contact with the hull projection so that it could be repaired or replaced. Therefore, the intermediate ring should include devices to retract individual wheel assemblies. To counter these difficulties, an alternative to the wheel bearing was proposed. Instead of wheels, the intermediate ring could hold electromagnets. This would replace the mechanical forces requiring physical contact with electromagnetic forces requiring only proximity of the electromagnets to the hull projection. Absence of physical contact would eliminate friction, fretting, fatigue, and lubrication problems. Should the separation between the electromagnets and the hull projection have to be small, however, the design would require control systems to keep the two apart in spite of any sudden motions of the hull relative to the shield. The ES group also wondered if such an electromagnetic bearing would require superconducting components. Should the power to the electromagnets fail, the system would need a backup mechanical replacement such as a set of retractable wheels. Whether wheeled or electromagnetic, the closed bearing system would apply forces to the shield. Some would be centrifugal forces
RkJQdWJsaXNoZXIy MTU5NjU0Mg==