Book of Abstracts- Lunar Regolith Simulant Materials Workshop

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EVOLUTION OF THE LUNAR REGOLITH. David S. McKay, Johnson Space Center, Mail Code KA, Houston TX 77058, david.s.mckay@nasa.gov Introduction: In order to properly design and produce simulants, it is necessary to have some insight into the evolution of the lunar regolith. In particular, the physical and engineering properties of the lunar regolith result from the complex processes that produce it and make it unique. In addition, the chemistry of the lunar regolith depends not only on the chemistry of the bedrock underlying it, but also on the evolution paths that produced it. In general, the chemistry of the regolith does not exactly correspond to the chemistry of the underlying bedrock. Furthermore, the chemistry of a given grain size fraction is likely to be different from that of another fraction. To understand these complexities, we must consider how lunar regolith has formed over geologic time. The lunar regolith. The lunar regolith is the fragmental layer that overlies nearly all rock formations on the moon. It varies in thickness from less than a meter in some areas to 10s of meters elsewhere. The maximum thickness is not known but is likely to be less than 100m and certainly less than 200m. Meteorite bombardment and secondary processes related to bombardment mainly produce the regolith. However the regolith is not simply ground up or milled bedrock. It is a dynamic material, sometimes becoming finer and other times becoming coarser in grain size. At any site the regolith may reach a steady state grain size but this grain size will likely differ from site to site. One type of regolith, represented by the black and orange glass at Apollo 17, is not the primary product of meteorite bombardment, but was produced by volcanic eruption of pyroclastic ash. In some places it constitutes the main regolith and is termed dark mantle. Dark mantle has many qualities that make it an attractive resource target for lunar propellant production. Typical lunar regolith contains rock fragments, mineral fragments, and glass. The primary glass type is agglutinates, which are constructional particles produced by small impacts. Because constructional particles are produced, the lunar regolith is not simply a product of grinding; its grain size distribution is much more complex. Figure 1 [1] shows the mean grain size and graphic standard deviation for 42 Apollo 17 soils. Finer Soils. These parameters show an inverse correlation; finer soils are better sorted. The maturity of lunar soils was first defined by this figure based on grain size parameters. Maturity is an important parameter because it determines how much solar wind components (hydrogen, carbon, nitrogen, etc.) are present. Independent measurements of agglutinate content showed that more mature soils have more agglutinates. This correlation is also shown in Figure 2. Mature Soils. The most mature soils contain more than 60% agglutinates in the intermediate size fraction 90-150µm. Extrapolation to 100% agglutinates would predict a mean grain size of 13µm. This is much finer grained than any Apollo soil; a soil this fine is unlikely 5
to exist on the moon. Figure 3 shows complete size distribution histograms for a number of soils and for several kinds of reference material. Immature Soils. Immature soils (e. g. 71061) are often bimodal and mature soils are usually single modal with narrower standard deviation. The volcanic soil 74220 is more fine grained and has the lowest standard deviation of any measured lunar soil. Yet it has no agglutinates. This radical disconnect between maturity-related properties means it was clearly produced by a radically different process compared to typical soils. Also note that lunar soils do not match the size distribution of either single impact communition or of calculated multiple impact communition. The essential difference is mainly the result of the role of constructional particles. Figure 4 illustrates the end-member path that soils take on the moon with repeated bombardment. One result of this mixing is that different grain size fractions may consist of subsets of differing maturity; these subsets or fractions of the complete soil may then have their own fractional maturity. Figure 6 shows the resultant of the mixing of two soils of differing maturity. The fine-grained part is dominated by one soil and the coarse-grained part is dominated by the other soil. If the parent soils are different initial compositions, the chemical and mineral composition of the resulting size fractions may differ radically from coarse to fine. Because communition and agglutination may occur at differing rates, a typical soil may reach equilibrium between the two processes (Fig. 7). Mixing of Soils. Large blocks produced from bedrock are ground down and become more mature. The final result is a balance between destructional particles and constructional particles. In this path, essentially all components have the same maturity. The other end member (Figure 5), represented by many soils, includes significant mixing of soils of differing maturities. However, if the supply of coarse particles is greater for one soil, its equilibrium point may be different from another soil. Hence, this equilibrium is really a dynamic steady state set by the supply of coarse 6
Page 2 and 3: The Lunar Regolith Simulant Materia
Page 4 and 5: Table of Contents Abstracts listed
Page 6 and 7: THE STATUS OF LUNAR SIMULANT MATERI
Page 8 and 9: PHYSICAL AND CHEMICAL CHARACTERISTI
Page 12 and 13: grained material which is in turn a
Page 14 and 15: Fig. 2 Fig. 3. “One Simulant Does
Page 16 and 17: quired to produce large volumes of
Page 18 and 19: stiffness properties of lunar regol
Page 20 and 21: for major and trace analysis of bul
Page 22 and 23: in the USGS analytical laboratories
Page 24 and 25: THE MOON AS A BEACH OF FINE POWDERS
Page 26 and 27: THE EFFECTS OF LUNAR DUST ON ADVANC
Page 28 and 29: Different simulants may be required
Page 30 and 31: SINTERING, MELTING AND CRYSTALLIZAT
Page 32 and 33: TOWARDS LUNAR SIMULANTS POSSESSING
Page 34 and 35: LUNAR REGOLITH SIMULANT REQUIREMENT
Page 36 and 37: SPACE RADIATION AND LUNAR REGOLITH.
Page 38 and 39: Figure 2. Logarithm of the Solubili
Page 40 and 41: Attendees Mian Abbas NASA/MSFC NSST
Page 42 and 43: Attendees Bill Carswell Cherokee Na
Page 44 and 45: Attendees Jim Gaier NASA Glenn Rese
Page 46 and 47: Attendees Paul Lowman Goddard Space
Page 48 and 49: Attendees Donald Sadoway Massachuse
Page 50 and 51: Lunar Regolith Simulant Materials W

Book of Abstracts- Lunar Regolith Simulant Materials Workshop

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