6.14 VI.4: SHIELDING, SUNLIGHT, AND WINDOWS VI. 4.1: General Remarks: The major design inputs and decisions involved in providing shielding and sunlight to the hull configuration in Figure 6.6 are flowcharted in Figure 6.7. VI.4.2: Shielding Requirement: The colony's location at LS exposes it to a radiation environment harmful to human life. To bring this radiation to an acceptable level, the design requires an enveloping shield with an area density of 5000 kg/m 2 . A description of the radiation environment and the calculations leading to the shielding area density figure appears in Appendix VI.A. To envelop the hull, the minimum mass required is the product of the hull area and the area density: (Minimum shield mass) (5000) (6.28xl0 4 + l.26xl0 5 ) 9.44xl0 8 kg Were this mass to spin with the hull at 2 to 3 RPM, it would develop a considerable centrifugal force requiring support structure to keep it together. The study group anticipated that this structure would complicate fabrication, requiring additional refined material and more sophisticated assembly techniques than an unstressed shield. Thus the ES group rejected the idea of a shield integral with the hull. The more desirable alternative appeared to be a shield separate from the hull, either stationary ("despun") or spinning very slowly. Given that the hull would spin within an enveloping shield, the ES group next considered the question of the relative orientation of the hull and shield. There were two options: free or fixed. In the free orientation option, the hull's spin axis would be allowed to point anywhere on the shield's inner surface. Figure 6.8 shows such a design. The hull would be contained within a spherical shield but its spin axis would be free to point in any direction and to wander around. In the fixed orientation option, the spin axis would be required to point at a specific spot on the shield surface (within some angular
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