8. 6 To absorb solar and galactic radiation, 5000 kg/m 2 of shielding is required over the entire hull surface. The structure itself contributes 630 kg/m 2 from both hulls and 4370 kg/m 2 of extra shielding sits in the hull compartments, against the outer hull. This extra shielding masses about 8.94xl0 8 kg. Slag is acceptable for this shielding and the refining process generates more slag than is required. VIII. 3: REFINING VIII.3.1: Refining Processes: Despite our lack of experience in space refining, it appears that features of the space environment can aid refining there. Advantages of space refining lie in availability of zero to high gravity (using centrifuges), very high vacuum, solar process heat, and abundant electric power. In combination, these permit the use of novel unit processes, such as ferrous alloy distillation (8.1). The main disadvantages are weight penalties from transportation of equipment to LS and the necessity of recycling most process chemicals. A flow chart of the total processing system is shown in Figure 8.2. Incoming lunar rock is pulverized to increase surface area, then reacted with hot hydrogen, yielding water, hydrogen gas, and oxides mixed with colloidal iron particles. A final reduction with carbon and physical separation by centrifuge yield the desired metals which are distilled into relatively pure iron, silicon, and a few minor elements. Hydrogen and carbon are recovered from the reactor by-products water and carbon monoxide, and recycled. Oxygen is a major by-product of the processing system. The refined iron is 99.95% pure iron of vacuum-melt quality (plus the added alloying elements). The main contaminant is likely to be silicon, but this is a necessary alloying element anyway. A solid continuously-cast piece of steel can be produced if desired. VIII.3.2: Process Mass, Power, and Labor: Assuming a feed stream of Apollo 15 landing site composition, the processing system requires 7.36 kg rock per kilogram of iron produced, yielding by-products of 5 kg slag, 0.86 kg oxygen, and 0.5 kg metallurgical grade silicon.
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