6.61 should be on or near the spin axis, so that the shield cutouts could stay as small as possible. Referring to Figure 6.21, this thermal path should, therefore, be either around the cargo airlock or around the light window. Two possible general configurations for the external radiator, a disc and a cylinder, are shown in Figure 6.25. The disc is assumed to radiate from both sides, the cylinder from its outside surface; both assumed radiative surfaces have area 7.73xlo 4 m 2 . There are structural problems inherent to these configurations. Section VI.5.2 described the hull as gyroscope. The attached spinning radiator would also be a gyroscope but with an angular momentum different than that of the hull. When a torque would be applied to the whole system (for example, by activity within the hull as described in Section VI.5.3), both gyroscopes would try to precess. The expected rates of precession would be given by: ()hull L Hhull L Hrad where Lis the torque applied, ()hull and ()rad the rates of precession of hull and radiator, and Hhull and Hrad the angular momenta of hull and radiator. Since Hrad was expected to be smaller than Hhull' its expected rate of precession ()rad would be far larger than ()hull" Since the hull and radiator were constrained to move together by their connecting structure, however, the situation would apply loads to that structure. Moreover, these loads would vary with the uncontrolled torques applied to the system, leading to fatigue of the materials in the connecting structure. Considerations of safety further complicated the external radiator design. A complete failure of the radiator was unacceptable since it would either raise the temperature of the hull or force the inhabitants to cut off the sunlight to their agriculture. Partial failure of the radiator was permissible since the final radiator design would have a safety margin in its area, but repair
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