6.60 The Stefan-Boltzmann Law then gives the radiator area: Poutputrad (£) (a ) (Trad) 4 Setting the mass flow rate at 1000 kg/sec (so that the total mass of the hull's air flows through the external radiator in one hour), then: Toutlet 269°K 281°K 7.73xl0 4 m 2 Appendix VI.G discusses radiator densities. A radiator at 295°K or below can be made of aluminum, and its area density is then 8 kg/m 2 . The mass of the passive external radiator would, therefore, be: Mrad = (Arad) (8) = 6.18xl0 5 kg The size of the radiator was not the only drawback to the concept. The ES group could not devise a safe rotating pressure bearing through which the hull's air could be pumped to and from the radiator. It was felt that a rotating pressure seal would eventually leak and break, pose major maintenance and repair problems, and seriously endanger the colony if it failed. Neither could the ES group devise any other kind of thermal path which could carry the power from the spinning hull to the not-spinning radiator. It was therefore concluded that the external radiator would have to spin with the hull. This decision limited the possible configurations. The radiator itself should be symmetrical about the spin axis. The thermal path from hull to radiator, since it passed through the despun shield,
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