and even less zinc may be in the ore, this rather efficient “winnowing” concentrates alkalies and zinc or zinc oxide in specific zones of the furnace, where they may decrease the permeability of the charge and cause serious reactions and deterioration of the blast furnace refractories. Similar problems may not arise in the lunar ore processing, but they should be carefully considered and avoided by appropriate design or operation. LUNAR EXPLORATION FOR SUITABLE MINING SITES In order to obtain several different materials from one mining site on the Moon, it has been suggested that this site be near the contact between the highlands and the mare. This suggestion is appropriate, but in reviewing some of the literature on potential lunar mining, I believe that too much reliance has been placed on a simple bimodal composition for lunar surface materials — anorthositic in the highlands and basaltic in the mare. The picture is actually more complex than that. For example, the mare basalts range from < 1 to ~ 13 wt.% TiO2 and from 6% to 16% MgO (14), and lunar soils formed on these can be expected to vary similarly. However, this is the variation among basalts sampled by Apollo 11, 12, 15, and 17 only, and these compositions are highly unlikely to be the extremes. In fact, the basalts from the Soviet Luna 24 site differed considerably from all of the above. Similarly the anorthositic breccias of the highlands range widely in their ratio of plagioclase to mafic minerals such as olivine and pyroxene, as well as in the content of minor but important elements such as potassium, both within a given site and globally, as is evident from the various orbital lunar analyses. The variations mentioned above are essentially areal variations. However, a lunar mining operation would probably take a vertical section of one or more meters of soil, so knowledge of the variation of composition with depth is essential. The surface composition is not always a good predictor of composition at depth, and core samples, perhaps made by a remotely operated drill, will be essential. Such three- dimensional control is even more important if the center of the mining operation is to be set up on the border between highlands and mare, as this is exactly where vertical changes are most likely. The problem of the exploration strategy to use in the search for a good site is not as trivial as it is sometimes portrayed to be. Arnold and Duke (15) evaluated many of these ramifications and proposed some specific steps. GENERAL NATURE OF NEEDED MATERIALS; USE IN TENSION VS COMPRESSION Demandite Criswell and Waldron (1) and Waldron et al. (12) have applied the concept of the imaginary molecule of demandite, corresponding to the gross composition of the nonrenewable resources humans use in a given economy (16), to the problem of the availability of materials in space for an SPS. They find that because the lunar soils are composed of ~85%^90% of the nonfuel, nonrecoverable elements used by United States industry, and because these materials can be obtained from the Moon at a
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