6.72 Since hull and shield were separate with no electrical pathway between them, each would need its own generating equipment or power storage system to run its operations. Shield operations involving humans would first require that the workers exit the hull and despin themselves. Section VI.8.3 and Appendix VI.F describe the thermal problems inherent in the separate shield concept. The proposed solution-- including heat pipes through the shield to improve its thermal conductivity--led to shield fabrication, inspection, and repair difficulties (Figure 6.29(d)). As Figure 6.29(d) shows, the colony concept had become far more complicated than the single-walled hull idea it had stemmed from. The FT group now was faced with the task of building three concentric shells: a hull floating inside a pair of thin metallic shells sandwiching 2.5 meters of lunar dirt. This shield would be studded with heat pipes throughout. This complicated fabrication scenario would be followed by a difficult up-spin sequence and an operational lifetime marred by disruptive leaks, tricky repairs, and the ever-present danger of collision between hull and shield. These predictions suggested a configuration change. VI.9.2: Changes: The alterations to the overall design which the study group made at this time led to the final configuration of the MIT Prototype Space Colony. The study group first eliminated the separate-hull-and-shield concept and replaced it by a compartmented double-hull. The shielding is included in the compartments as shown in Figure 6.30. This new hull configuration eliminates a number of problems. A leak in either the inner hull, the outer hull, or the compartment bulkheads does not cause loss of the hull's inner atmosphere and therefore does not disrupt colony operations. Repair is simpler since it can take more time and because the damaged plates can have equal pressures on both their faces. As described in Section VI.9.1, oscillations and their effects are far less severe in a compartmented double-hull than in a singlewalled hull. This reduces the changes of plate failures due to dynamic stresses. The compartmented double-hull can also withstand
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