Mathematics – Logic
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999nvm..conf....1a&link_type=abstract
Workshop on New Views of the Moon 2: Understanding the Moon Through the Integration of Diverse Datasets, p. 1
Mathematics
Logic
Helium Isotopes, Lunar Resources, Lunar Soil, Oxygen, Oxygen Production, Correlation, Life Support Systems, Clementine Spacecraft, Lunar Prospector
Scientific paper
Laboratory experiments have demonstrated correlations between the abundances of some lunar resources and specific chemical and mineralogical parameters of surface materials. Global remote sensing from the Apollo, Galileo, Clementine, and Lunar Prospector missions, combined with Earth-based observations, has now quantified these parameters. Combining experiments and remote sensing allows the first prospecting for resources across the entire lunar surface. The Moon's rocks and soil contain resources that could be used to support a future lunar base for research or for launching expeditions into deep space. Lunar O is the resource most likely to be exploited first, for both propulsion and life support. The efficiency of O extraction from lunar materials has been shown to depend strongly on the material's chemical and mineralogical composition.Some lunar materials may be rare and vital enough on Earth to justify the cost of their return. The rare isotope He-3, which can be used in an efficient and low-polluting fusion power reaction, has been cited as one such resource. Over 20 different processes have been proposed for O production on the Moon. Among the simplest and best studied of these processes is the reduction of oxides in lunar minerals and glass using H gas. It was reported that the results of O extraction experiments on 16 lunar soils. Each sample was reacted in flowing H for 3 h at 1050 C. Total O yield correlated strongly to each sample's initial Fe2+ abundance. A linear least-squares fit of O yield vs. Fe2+ for 16 lunar soils yielded a regression line with a slope of 0.19, an intercept of 0.55 wt% O and an r-square value of 0.87. Oxygen yield did not significantly correlate with the abundance of any element except Fe. Thus, O yield from lunar soils can be predicted with nearly 90% confidence based solely on their iron abundances. The potential for O production at any location on the Moon can be predicted if the soil's Fe concentration is known. On a global scale, Fe concentration in the near surface has been estimated from data returned by a variety of spacecraft. Iron was one of several elements measured from near equatorial orbits during the Apollo 15 and 16 missions, using gamma ray spectrometry. These data covered approximately 20% of the lunar surface, with spatial resolutions of about 100 km. An improved gamma ray spectrometer and a neutron spectrometer, flown on the Lunar Prospector spacecraft in a polar orbit, provided Fe abundance data for the entire lunar surface, again at a spatial resolution of about 100 km. A technique for iron assessment based on orbital multispectral imaging has been developed. This method correlates Fe abundance to a parameter derived from reflectance values at 750 and900nm. The authors use data from the Clementine spacecraft to map Fe abundances across nearly the entire lunar surface. These data can support identification of Fe-rich regions as small as a few hundred meters across. Researchers find good agreement between gamma-ray/neutron and multispectral Fe determinations for most areas on the Moon. The H-reduction experiments cited above also showed submillimeter volcanic glass beads could be highly desirable feedstocks for lunar O production. Iron-rich species, represented by glassy (orange) and crystalline (black) beads, promise particularly high O yields. Apollo 17 volcanic glass sample 74220, composed predominantly of orange glass beads with an average diameter of 40 mm, contains 17.8 wt% Fe2+. Reduction of this sample yielded 4.3 wt% O, well above the regression line defined by the experiments on 16 lunar soils. Sample 74001 is dominated by black crystalline beads, the isochemical equivalent of orange glasses. Reduction of 74001 yielded 4.7 wt% O, the highest value for any lunar sample. Extensive areas of the lunar surface covered by volcanic glass beads have been delineated using Earth based data and spacecraft orbital photography. Chemical compositions of the deposits have been estimated and mixing ratios of glassy and crystalline glass beads have been determined. Clementine multispectral imagery has been employed to determine the precise extent and estimate the thickness of one widespread deposit, that of the Aristarchus Plateau. Lunar ice could prove to be a highly advantageous O source, compared to O derived from soil reduction, in terms of process complexity and power requirements. Thus, a deposit of ice on the Moon is a potentially important resource.Permanently shadowed polar craters have been modeled as possible cold traps for water ice, derived either from indigenous sources or from comets. Any lunar ice deposits must occur in extremely restricted areas near the poles. Only crater interiors that are permanently shadowed from sunlight are cold enough to have retained volatiles for a significant part of the Moon's history. Clementine images and Earth-based radar have demonstrated that craters whose interiors are never exposed to sunlight do exist near the lunar poles. Water ice has been tentatively identified in some of these craters using Clementine bi-static radar data. Lunar Prospector mapped the epithermal and fast-neutron fluxes across the entire Moon. Low epithermal fluxes are correlated with concentrations of H, and by extension ice, in the near-surface. Such signatures were observed near permanently-shadowed craters at both lunar poles. Calculation of the actual amount of water ice in these cold traps is strongly model-dependent but each polar region could contain as much as 3x109 t of water ice. The concentration of solar wind-implanted He in mare regolith increases with the soil's Ti content. This correlation is apparently due to preferential adsorption of He by ilmenite grains. Thus, Ti in mare soils is a predictor of the He-3 resource. Additional information is contained in the original.
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