6.55 VI.8.3: Output by Passive Radiation through the Shield: The ES group first considered removing power from the hull by passive radiation. "Passive" indicates that the energy is a_llowed to flow without the interference of energy-driven devices such as heat pumps. The ES group first calculated the radiation output of the hull alone. This is governed by the Stefan-Boltzmann Law: Poutputhull = (£) (cr) (¾ull outside) (Thull outside) 4 where ( £ ) = emmisivity [taken to be (.9), the value for white paint (6.6)]; (cr) = Stefan-Boltzmann constant= 5.74xl0-B watts/m 2 -(°K) 4 ; Ahull outside= outside area of the hull; Thull outside= temperature of outside surface of the hull (assumed to be 295°K, close to or equal to the inside temperature). Therefore, P = 7.39xl0 7 watts outputhull Since the thermal control was passive in this case, Pthermal O. Then, P = 3. 35xl0 7 watts inputtotal Thus, if the hull were radiating directly into space, we would have more than twice the needed output. However, the radiation from the hull's surface had to travel through the shield before reaching space. Figure 6.23 schematizes the effects involved. The radiation from the hull warmed the inner surface of the shield. This surface transmitted energy through the shield by convection and radiation (convection through the lunar dirt particles and radiation across the vacuum gaps between those particles), but also reradiated part of the energy back onto the hull. The outside surface of the shield radiated power into space. Appendix VI.F presents calculations describing this power flow from the hull, through the shield, and into space. The total areas of hull and shield are taken as radiative surfaces and these areas
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