Return to an Apollo Site
Even with our current knowledge of the Apollo sites, we need additional information to assess their suitability for mining. For example, even at the best characterized site, Apollo 17 (fig. 13), small- to medium-scale (in meters) variability in composition and particle size is not sufficiently well known. Because such characteristics profoundly affect the success of a mining and ore processing venture, many more regolith cores would need to be collected before a mine was specifically located within the area where Apollo 17 landed. The coring locations would be chosen so as to define a grid over each prospect. Each block in the grid would be on the order of several meters square by 2 meters deep. Variations in grain size and mineralogy across the grid would be used to assess the suitability of a specific prospect.
From the Apollo 17 site at Taurus Littrow, we have the largest suite of samples and we also have the onsite observations of geologist- astronaut Jack Schmitt. By designing flexibility into mining and processing equipment, we can eliminate the need for some of the data normally required.
The chief feedstock at the Apollo 17 site would be the iron- and titanium-rich mare basalts. This "ore" could be scraped from the surface and provided as bulk material; oxygen and metallic iron could be extracted from it; and ceramics could be made from it- all with relatively simple mining, beneficiation, extraction, and processing procedures. However, even the simplest resource operations present difficulties on the lunar surface and require the support of a sophisticated transportation system and the presence of human beings.
Oxygen Production
All of the major rock types we have found on the Moon offer the potential for oxygen production in large quantities. However, ilmenite-rich mare basalts, such as those at the Apollo 17 site, seem to offer the widest range of production methods, including ilmenite reduction. Adequate separation of the ilmenite from the silicates in these basalts could be a problem. Because the ilmenite- rich soils at this site derive from basalt flows, the ilmenite crystals are both fine-grained and intergrown with silicate crystals. An answer to this separation problem might be to use an oxygen production process (such as magma electrolysis or the carbothermal reduction of silicates) which does not require beneficiation (mineral concentration).
Metal Extraction
Iron seems to be the metal mQ$t easily obtained from lunar rocks. It can be obtained as a byproduct of the direct hydrogen reduction of ilmenite and possibly by other methods. Mare basalts, relatively rich in iron and titanium, provide the best large-scale source known on the lunar surface. The basalts at the Apollo 17 site are thus an adequate source of iron.
Bulk Material
While bulk material is avai)able at virtually any lunar location, a site with a deep, relatively fine-grained regolith is preferred from the point of view of moving large amounts of material. The Apollo 17 site provides adequate access to this resource.
Other Site Considerations
Proximity to highlands: Although we anticipate that the first lunar resources used on the Moon will be obtained from mare soils, it may be that. in the long range, materials such as aluminum, lime, and certain ceramics may best be obtained from highland rocks. Thus, selection of an initial lunar mining and processing site close to lunar highlands seems prudent. This requirement would also be satisfied by the Apollo 17 site (see fig. 14).
New Sites
In terms of currently recognized lunar mineral resources, there is very little justification for developing a site other than an Apollo site. If, however, water were located in the polar regions, then a water-bearing site would have a higher priority than any other site. Evaluation of resources at a site or sites other than an Apollo site would require implementation of a regional exploration program. This program would include the discovery phase, presumably by an orbiter mission, in which a number of potentially favorable mining sites would be identified, each with multiple prospects. This phase would be followed by an unmanned surface mission or missions to several of the most favorable sites. Such a mission would include a Rover-type vehicle capable of obtaining regolith cores at least 2 meters deep and returning the samples to Earth. Follow up manned missions would land at one or two places from which candidate mining sites are accessible.
The objectives of the earliest manned missions would be to set up an exploration base and, operating from that base, to carry out a rigorous sampling and evaluation program at a small number (no more than 5 or 6) of the most favorable prospects. From this evaluation, all the prospects found to be ore bodies would be ranked from most to least favorable on the basis of mining and milling criteria. Final site acceptance would factor in accessibility, potential hazards, power requirements, and the myriad of site details required by any mining operation.
Conclusion
Any otherwise acceptable mining site on the Moon should have adequate resources to support a 1O-year. 40 OOO-metric-ton-per-year operation. Of the sites sampled. that of Apollo 17 is the best characterized and should require the least pre-development work. Only a site having frozen water would be more desirable. Even though the Apollo 17 site is the best characterized of the sites, pre-development work involving extensive coring of the regolith.is required to assess its physical and compositional variability.
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