Apollo sample and high- and low-ti lunar soil simulants MLS-1A and JSC-1A: Implications for future lunar exploration

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1 JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112,, doi: /2006je002767, 2007 Apollo sample and high- and low-ti lunar soil simulants MLS-1A and JSC-1A: Implications for future lunar exploration Eddy Hill, 1 Michael J. Mellin, 1 Bill Deane, 1 Yang Liu, 1 and Lawrence A. Taylor 1 Received 7 June 2006; revised 28 August 2006; accepted 6 October 2006; published 16 February [1] Plans for establishment of a manned lunar base make it imperative that considerable research be performed on the use of lunar rocks and soil for in situ resource utilization (ISRU). Samples and simulants of lunar soil must be established for these studies. We present here the bulk and mineral chemistries of unusual Apollo 17 sample 70051, the <45-mm fraction of 70051, and the bulk and mineral chemistries of lunar soil simulants MLS-1A, JSC-1A, and JSC-1Af. Comparison to lunar soils collected during the Apollo missions shows that has bulk chemistry similar to that of soils from the North Massif bounding the Valley of Taurus-Littrow. Particle-size distribution reveals to differ significantly from bona fide lunar soils. It is a coarse, immature sample with >80 % of particles >50 mm, and a constrained range of particle sizes (50% of particles are mm in size) when compared to typical Apollo 17 soils (e.g., 71501,1 has 20% of particles in the mm range). Plagioclase, present in rock fragments and as mineral fragments (up to sizes 1 mm), is the main phase present (50.5 vol%). Simulant JSC-1A has a chemistry that is atypical for most of the Moon and contains 49.3 vol% glass. Simulant MLS-1A resembles the FeO, TiO 2 and Al 2 O 3 contents of mare basalt soils. Both lunar soil simulants have specific properties for certain in situ resource utilization studies, however, neither fully matches both the physical and chemical characteristics of lunar soil. Sample 70051, as a 1.4-kg haphazard mixture of lunar soil particles, is probably the best of the Apollo soil samples to be allocated for various ISRU investigations, where the uniqueness of lunar soils is deemed a necessity for study. Citation: Hill, E., M. J. Mellin, B. Deane, Y. Liu, and L. A. Taylor (2007), Apollo sample and high- and low-ti lunar soil simulants MLS-1A and JSC-1A: Implications for future lunar exploration, J. Geophys. Res., 112,, doi: /2006je Introduction [2] Several countries are actively pursuing plans for manned missions to the Moon, then on to Mars, and beyond. As such, there are many material science and engineering studies that must be conducted to plan for the in situ resource utilization (ISRU) of lunar materials, as we learn to live-off-the-land on the Moon. These studies are in need of lunar soil simulants and even some Apollo samples for experimentation, necessitating the characterization of suitable samples for such investigative endeavors. For example, sustained human presence on the Moon is dependent on the availability of oxygen, and space exploration will be made more affordable by production of the required propellants (e.g., LOX, LH) on the Moon, rather than incurring the cost of transportation from Earth (currently estimated at $25,000 per pound). Studies of ISRU are currently underway to determine how to best obtain these products from the lunar soil. [3] Processes under consideration for ISRU of lunar materials are dependent on the engineering properties that 1 Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee, USA. Copyright 2007 by the American Geophysical Union /07/2006JE micro-meteorite impacts have imparted to the agglutinates, vapor-deposited glass, and nanophase Fe 0 (np-fe 0 ) found in the lunar soil, as well as to the bulk chemistry and mineralogy of the latter. ISRU investigations may require the use of lunar soil, obtained during the Apollo missions, or materials that can faithfully reproduce its properties. Lunar samples are too precious for large-scale tests involving hundreds of grams of material. However, a unique Apollo 17 soil sample with an unusual collection history and constitution may be available for experimentation where lunar simulants are totally insufficient. We suggest using this lunar sample in the final stages of ISRU investigations, once procedures have been advanced and the final, fine-tuning stage has been reached. Initially, lunar soil simulants such as MLS-1A (Minnesota Lunar Simulant), and JSC-1A (Johnson Space Center Lunar Soil Simulant) should be used. MLS-1A was produced as a site specific simulant and approximates the bulk chemical composition of a high-ti Apollo 11 soil, (Table 1). MLS-1A was derived from a wholly crystalline, high-ti hornfels in Duluth, Minnesota. It was intended for studies where chemical similarities to high-ti lunar soil are of concern, but it does not reproduce the engineering characteristics of lunar regolith. As originally produced, MLS-1A contained no glass, an essential component for any lunar soil simulant. In an attempt to better approximate the 1of11

2 Table 1. Bulk-Chemical Compositions of Lunar Soils and Lunar Soil Simulants a BIR-1 Pub b BIR-1 Msd b <45-mm USGS JSC-1Af c JSC-1 JSC-1A JSC-1Af MLS-1A d d SiO (6) 42.8 (2) TiO (1) 6.77 (1) Al 2 O (2) 12.1 (3) Cr 2 O Fe 2 O FeO e 11.2 e 10.3 e (1) 16.3 e (1) MgO (1) MnO CaO (1) 11.1 (1) Na 2 O (1) 2.22 (2) K 2 O (3) P 2 O (1) LOI 0.70 Total a Numbers in parentheses represent one sigma variance in averaged analysis in terms of the least figure cited. b BIR-1: Pub, published and Msd, measured compositions. c JSC-1A Material Safety Data Sheet [Orbital Technologies Corporation, 2005]. d Morris et al. [1983a, 1983b]. e Total Fe as FeO. qualities of lunar soil, portions of MLS-1A were melted, quenched, and ground; this glass was then added to the simulant [Weiblen et al., 1990]. Unfortunately MLS-1A is not available at present, but plans have been made for renewed quarrying of this lunar simulant. [4] Lunar simulant JSC-1 was produced in 1993 to facilitate engineering studies in preparation for human activities on the Moon; as such, it was deemed necessary to have a material that contained a high proportion of natural glass. JSC-1 was produced from a glass-rich (50 vol%) basaltic tuff and approximated the particle-size distribution and engineering properties of a lunar Apollo 14 soil [McKay et al., 1994] (Table 1). JSC-1 was used for studies of material handling, construction, excavation, dust control, spacesuit durability, oxygen production, and sintering to produce building blocks. Supplies of JSC-1 have long been exhausted, but production of a new simulant, JSC-1A, from the same quarry source, has commenced. To date, however, only the <20 mm fraction of JSC-1A (JSC-1Af) is available. We describe both JSC-1A and JSC-1Af in this work. [5] Although the bulk-chemical compositions and engineering characteristics of the previous simulants have been characterized [McKay et al., 1994; Tucker et al., 1992], these are no longer in supply, and a detailed knowledge of mineral compositions of new simulants is required; particularly of the new production of JSC-1A. Our understanding of processes such as oxygen production and solar wind recovery is dependent on our knowledge of the components of simulants, i.e., the chemical compositions and abundance of the constituent minerals. Furthermore, the unforeseen presence of chemical elements in the simulants may result in unwanted and unexpected results that would not translate adequately to applications on the lunar surface. For example, during hydrogen reduction, released O is bonded with HtoformH 2 O. This is later electrolyzed to separate H from O. However, if S is released into the system owing to the breakdown of sulfides, this would result in the formation of SO 2 or H 2 S and could interfere with function of the electrolysis unit. Therefore prior knowledge of the presence of sulfides allows for appropriate measures to be taken to prevent this deleterious side effect. [6] Since not all phases present in a lunar soil or simulant are affected in the same way or to the same extent by the different processes that may be applied, it is not sufficient to know only the bulk composition of the system but we must also be aware of the mineral compositions. Detailed knowledge of the chemistry and mineralogy of simulants and their lunar soil counterparts will assist in the development of suitable solutions to the problems presented by a return to the Moon (e.g., dust mitigation, oxygen production, solar wind recovery, radiation shielding, drilling, excavation, impact tests). The standardization and production of suitable lunar soil simulants will allow for direct comparison of the results obtained by various groups working on these problems. This in turn will lead to a better understanding of how the different processes devised on Earth will eventually be applied on the Moon. In this contribution, we report the petrography and bulk-chemical composition of MLS-1A, JSC-1A, and JSC-1Af (<20-mm-size fraction). We also provide a description of the petrography, particle size distribution, and analysis of the bulk chemistry of Apollo 17 soil (<1 mm) and the <45-mm fraction of this lunar sample, as these are potential samples for specialized ISRU studies. 2. Provenance of [7] Sample has an unusual collection history. The Apollo 17 landing site was situated between two highland massifs, in the Valley of Taurus-Littrow, at the southeastern margin of the Mare Serenitatis basin (Figure 1). The site was chosen owing to the potential it presented for collection of rocks older and younger than those previously returned by the Apollo or Soviet Luna 16 and 20 missions. Samples from the north and south massifs, surrounding the Taurus- Littrow valley, were hoped to provide specimens of ancient highlands material, as well as provide an age for the Serenitatis impact event. Additionally, samples obtained 2of11

3 Figure 1. The Valley of Taurus-Littrow was chosen as the Apollo 17 landing site owing to the potential it offered for collection of samples older and younger than those previously obtained by the U.S. Apollo and Soviet Luna missions. In total, the mission accomplished three EVAs, during which samples were collected along the traverse area of the LRV. These included samples from the north and south walls of the valley. As a result, the back-right wheel of the LRV threw soil grains from all different terrains onto the back of the rover. from the valley floor would allow for the age and composition of the mare material to be determined. [8] As equipment was being loaded onto the Lunar Rover Vehicle (LRV), before the first extra-vehicular activity (EVA), the right-rear fender was torn off. This resulted in a plume of lunar regolith being thrown over the vehicle, as it traversed the Valley during EVA 1. The fender was partially repaired with a geologic map, duct tape, and a clamp; however, this did not completely mitigate all the roostertail dust from collecting on the LRV. At the end of the third and final EVA, it was noted that regolith had been accumulating on the Buddy Secondary Life Support System on the rear of the LRV. This material was collected, bagged, and originally labeled BSLSS. Subsequently, this soil sample (the portion of regolith <1 cm) was relabeled Lunar soils are typically sieved into size fractions, such that is everything <1 mm, is 1 2 mm, is 2 4 mm, and is 4 10 mm. Hence the <1-mm portion was labeled as 70051, with a total of 1438 g. As a sample collected from the back of the lunar rover, it lacks the scientific integrity of provenance but does represent a haphazard mixture of fractions of lunar soils over a broad sample of lithologies. 3. Methods [9] Major-element compositions of the lunar simulants, of 70051, and the <45-mm fraction of (Table 1) were determined using a Philips MagiX PRO XRF unit. Glass pellets were prepared for 70051, JSC-1, and MLS-1A. The <45-mm fraction of and JSC-1Af were fine enough to permit analysis of pressed pellets. Simulant JSC-1A was ground to a fine powder and a pressed pellet also produced. Use of a pressed pellet allowed for analysis of trace-element 3of11

4 Table 2. Trace-Element Concentrations <45-mm 70051, ppm JSC-1A, ppm <20-mm JSC-1A, ppm Ba Co Cr Cu Nb Ni Pb Rb S Sr V Y Zn Zr concentrations in these materials (Table 2). USGS Icelandic Basalt Standard BRI-1 (geo-reference material) was analyzed along with the above materials. In all cases, comparison of analysis with published values for this standard point to the high quality of the XRF analyses (Table 1). [10] Chemical compositions of glass and mineral phases, of the different simulants and lunar soil 70051, were obtained using a Cameca SX-50 electron microprobe. An energy potential of 15 kv with a 20 na beam current was used. Spot size was 1 to 10 mm for mineral and oxide phases, and 20 mm for glass analyses. Peak and background counting times of s. and standard PAP corrections were applied. Natural and synthetic standards were used for calibration and were checked regularly between sessions to ensure data quality. Detection limits (3s above background) are <0.03 for SiO 2,TiO 2,Al 2 O 3, MgO, CaO, Na 2 O and K 2 O; <0.05 for Cr 2 O 3, MnO, FeO, P 2 O 5, NiO, and V 2 O 3. The Cameca SX-50 microprobe was also used to obtain modal analyses (Table 3); performed using the method of Taylor et al. [1996]. This method involves use of an energy dispersive spectrometer (EDS) and the FeatureScan program of Oxford Instruments. Since the chemistry of every phase can be used to form an effective bin for the analyses, use of the EDS permits the identification of phases in 250,000 points on a polished thin section. Iteration of the number of spots counted for each phase, with the use of the FeatureScan software, provides modal abundances representative of the area examined in the sample. Fields of mm, with a pixel size of 1 mm, were scanned with analyses at 3-mm intervals, using a 0.5-mm beam size. 4. Results 4.1. Sample [11] The bulk chemistry of and the <45-mm fraction of are given in Table 1. Sample consists of various clasts of high-ti basalt, large mineral fragments (0.5 1 mm plagioclase), breccias, volcanic orange glass, and agglutinates (Figure 2). Coarse (crystal sizes mm) and fine-grained basalt clasts (<200 mm) contain pyroxenes > plagioclase > ilmenite > olivine. Microbreccias contain a minority of clasts 100 mm, with the majority of clasts measuring <50 mm. Clasts are mostly plagioclase and olivine. Agglutinates contain pyroxene and ilmenite fragments of 100 mm, and plagioclase 50 mm, held within vesicular, agglutinitic glass. [12] Modal analysis of revealed the major constituent to be plagioclase (Table 3), making up 50.5 vol% of the sample. In contrast, the major constituent of the <45 mm portion of is agglutinitic glass which makes up 40.6 vol%, versus 31 vol% for the bulk of Plagioclase content in the finer fraction is 30.2 vol%. Pyroxenes are the third most common phase present and make up 8.11 vol% and 15.2 vol% of and <45 mm 70051, respectively. [13] As part of the basalt clasts and agglutinates, pyroxenes span almost the entire range of compositions (Figure 3). Analyses of pyroxenes reveal concentrations of TiO 2 ( wt%), Al 2 O 3 ( wt%), and Cr 2 O 3 ( wt%). Plagioclase compositions contain up to 0.82 wt% FeO and are present in basalt clasts (An ), agglutinates (An ), microbreccias (An ) and lithic fragments (An ). Olivine compositions range from Fo in basalts and Fo 86 for clasts in microbreccias. Glass chemistries display a range of compositions with the volcanic glasses generally lower in SiO 2 and Al 2 O 3 but higher in TiO 2 and FeO than the agglutinitic glasses (Table 4). Traceelement concentrations (Table 2) of <45 mm reveal considerable Cr, S, and V, relative to bulk [14] Particle size distribution (Figure 4) for 70051, (140, 141, 142) shows this to be a coarse, immature sample. Over 80% of particles are larger than 50 mm, and approximately 50% of particles are between 50 mm and 100 mm in size. This is a much narrower range than that of any normally collected Apollo 17 soil, which show a relatively even size distribution between 250 and 20 mm (e.g., 71501,1 has 20% of particles in the 50- to 100-mm size range). Examination of the different size separates reveals obvious large plagioclase fragments in all sample sizes 125 mm, most likely a reflection of highland s plagioclase input Minnesota Lunar Simulant: MLS-1A [15] Descriptions of the original lithology and processing of lunar regolith simulant MLS-1A are given by Weiblen and Table 3. Abundance of Glass and Mineral Phases <45 m JSC-1A MLS-1A Glass Agglutinitic glass Volcanic glass K - glass SiO Cristobalite Feldspar Plagioclase Pyroxene Fe - cpx Pigeonite Augite Olivine Amphibole Fe-Ti Oxide Ilmenite Chrome Spinel Sulphide Troilite Apatite Clay minerals Biotite Sphene Total of11

5 Morey [1980], Weiblen et al. [1990], and Tucker et al. [1992]. Petrographic study of our sample of MLS-1A reveals pyroxene, olivine, and plagioclase crystals up to 400 mm in size. Ilmenite crystals up to 200 mm make up most of the Fe-oxide phases, with some smaller Ti-magnetite also present (Figure 5). Modal analysis of MLS-1A shows the major phases that make up this simulant are plagioclase (47.5 vol%), pyroxene (29.6 vol%), ilmenite (8.0 vol%) and amphibole (6.2 vol%). The sample of MLS-1A that we report on here was prepared specially by Paul Weiblen (3/2005) and is only that of the crushed rock, i.e., no glass additive, typical of the simulant that he distributed previously. Plagioclase compositions are An ; pyroxene compositions plot in the augite and orthopyroxene (bronzite) fields (Figure 3); olivines are Fo Sulfides present are chalcopyrite (CuFeS 2 ) and bornite (Cu 5 FeS 4 ). Average chemical compositions of the major-mineral phases are listed in Table Johnson Space Center Simulant: JSC-1A [16] Hand-specimen study of quarry samples of JSC-1A, prior to grinding, show this rock to be black, glassy, vesicular lava. Upon grinding, particles above 250 mm in size retain the physical appearance of the hand specimen, whereas finer fractions form an olive-brown powder. [17] Petrographic study of the quarry specimen of JSC-1A shows it to be a glassy, vesicular rock containing euhedral to subhedral phenocrysts of plagioclase (up to 400 mm) and olivine (up to 200 mm), set within a quench glass, containing smaller crystals (5 40 mm) of plagioclase, quartz, apatite, and clinopyroxene (Figure 5). In addition, JSC-1A contains euhedral to anhedral Ti-rich magnetite (Ti-magnetite) and chrome-spinel (Cr-spinel) up to 20 mm in size. Modal distribution analysis of JSC-1A (Table 3) indicates the three major constituents of this simulant are glass (49.3 vol%), plagioclase (38.8 vol%), and olivine (9 vol%). Average chemical compositions of glass and the major-mineral phases are listed in Table 6. Olivines in JSC-1A were determined to range from Fo 69 to Fo 85 in composition. Plagioclase ranges from An 64 to An 72. Pyroxenes are augites. [18] Trace-element concentrations (Table 2) differ between JSC-1A and JSC-1Af. Of note are the higher concentrations in JSC-1A of Ba, Sr, and S, versus JSC-1Af. The disparities in composition are likely a result of the differences in crushability of minerals holding these elements. 5. Discussion [19] With decreasing grain size of Apollo 17 soil, 70051, there is an increase in the bulk Al 2 O 3 content and the abundance of agglutinitic glass (Tables 1 and 3), consistent with the findings of Taylor et al. [2001]. Concurrent with 5of11 Figure 2. BSE images representing some of the lithologies encountered in Apollo 17 soil (a) Mineral and rock fragments are welded together by impact-generated glass to form an agglutinate with classical vesicular texture, formed by the escape of solar wind implanted particles during the impact-melting process. (b) Coarse-grained, high-ti basalt fragment containing px (pyroxene), plag (plagioclase), ol (olivine), chr (chromite), ilm (ilmenite), and cri (cristobalite). (c) Fine-grained fragment of high-ti basalt containing pyroxene, plagioclase, olivine, and ilmenite. (d) Breccia containing coarse-pyroxene fragments within a fine-grained matrix.

6 Figure 3. Compositional diagrams for plagioclase, olivine, and pyroxene from lunar soil and lunar soil simulants, MLS-1A and JSC-1A. As expected, lunar plagioclases are more anorthositic than their terrestrial counterparts. Of the latter, MLS-1A feldspars are the most alkalic. Olivine compositions range from Fo for 70051, Fo for JSC-1A, and Fo for MLS-1A. Soil presents an entire range of pyroxene compositions, from augite to pigeonite and Fe-rich pigeonite. Pyroxene compositions for MLS-1A and JSC-1A are more constrained, with MLS-1A containing augite and bronzites (opxs), and JSC-1A augite. the increase in agglutinitic glass, we predict an increase in the amount of nanophase Fe 0 present in this soil [Taylor et al., 2001], although, no measurements have been performed for np-fe 0. From a mineralogical standpoint, the lower plagioclase and higher olivine content of the <45 mm fraction of the soil suggests that bulk contains a larger component of coarse-grained highlands material. This observation is corroborated by the presence of large (500 mm to 1 mm) high-an plagioclase (An 95 ) fragments present in the sample. When compared to Apollo 17 soils (Figures 6a and 6b), shows a higher affinity with the chemistry of soils collected from the Northern Massif; rather than the 6of11

7 Table 4. Composition of Glasses and Major Mineral Phases in a Aggutinitic - Glass Volcanic - Glass Augite Pigeonite Orthopyroxene Plagioclase Olivine Ilmenite SiO (37) 38.9 (12) 49.9 (11) 51.3 (7) 54.2 (15) 44.6 (9) 38.5 (15) 52.8 (4) TiO (277) 9.51 (80) 1.34 (65) 0.82 (85) 0.48 (15) 0.05 (4) 0.09 (5) 0.04 (3) Al2O (51) 6.15 (12) 1.74 (29) 1.68 (14) 0.95 (36) 34.4 (125) Cr 2 O (15) 0.64 (23) 0.47 (21) 0.50 (31) 0.43 (19) 0.05 (7) 0.68 (12) FeO 11.6 (46) 21.6 (22) 16.2 (39) 18.1 (12) 13.1 (68) 0.22 (19) 20.2 (78) 42.8 (7) MgO 8.31 (296) 13.1 (26) 14.6 (23) 21.0 (2) 27.9 (51) 0.11 (10) 40.3 (64) 2.34 (45) MnO 0.34 (6) 0.42 (3) CaO 12.5 (18) 8.24 (152) 14.2 (37) 5.00 (41) 1.71 (23) 19.0 (7) 0.16 (13) 0.10 (11) Na 2 O 0.51 (36) 0.31 (29) 0.87 (4) 0.59 (37) K 2 O 0.14 (26) 0.07 (7) 0.08 (6) 0.04 (1) Total a Numbers in parentheses represent one sigma variance in averaged analysis in terms of the least figure cited. higher Al 2 O 3 and lower FeO and TiO 2 of the Southern Massif, or the higher FeO and TiO 2 mare soils of the valley floor. Comparatively, the high TiO 2 content of this sample places it firmly within the range of compositions expected for an Apollo 17 soil and above the range of compositions expected for Apollo 12 to 16 soils. When compared with other Apollo soils, on a FeO/Al 2 O 3 plot, the composition of plots within the values obtained for Apollo 15 soils and approximates those of Apollo 14 highland soils. [20] Despite chemical similarities with Apollo 17 type 3 soils [Rose et al., 1974; Rhodes et al., 1974] and closer proximity to the bulk compositions of North Massif soils, as well as to their trace element concentrations [Rhodes et al., 1974], it must be noted that is not a lunar soil, but a haphazard sampling of various soils. This is exemplified by its particle size distribution (Figure 4). As can be seen, soil is lacking in fines when compared to other Apollo 17 soils, and also contains a lower proportion of coarser particles. Unlike lunar soils, which have been sorted by continued comminution by meteorite bombardment, the particle size distribution of is most likely dependent on the sampling characteristics, sorting by vibration on the LRV, and the rooster-tail collection method. A certain amount of sorting would have been caused by the projection into space of different size particles thrown upward by the Figure 4. Particle size distribution of Apollo 17 soils modified from McKay et al. [1991]. Soil is a coarse, immature sample with over 80% of particles >50 mm. Normal Apollo 17 soils, in contrast, are well sorted, with more even size distributions. Figure 5. BSE images of JSC-1A and MLS-1A revealing their characteristic textures and mineralogies. (a) JSC-1A contains mainly plagioclase and olivine held in a glass matrix. Smaller crystals of clinopyroxene and Ti-magnetite are also present. (b) Coarser MLS-1A contains obvious plagioclase, pyroxene, olivine, ilmenite, and Ti-magnetite. 7of11

8 Table 5. Composition of Major Mineral Phases in MLS-1A a Plagioclase Olivine Ti-magnetite Ilmenite Cpx b Opx b Amphibole SiO (5) 35.4 (11) 0.05 (1) 51.3 (6) 52.1 (3) 39.7 (18) TiO (38) 50.0 (11) 0.51 (28) 0.26 (13) 1.51 (7) Al 2 O (4) 2.54 (16) 1.20 (28) 0.55 (4) 11.2 (10) Cr 2 O (5) V 2 O (4) Fe 2 O (6) FeO 0.50 c (19) 41.5 c (10) 37.4 (5) 45.9 c (3) 11.7 c (11) 25.9 c (6) 22.5 c (13) MgO 22.1 (17) 0.09 (1) 1.22 (23) 13.6 (2) 19.6 (6) 6.93 (121) MnO 0.58 (2) 0.19 (4) 0.55 (8) 0.32 (10) 0.55 (5) 0.24 (6) NiO 0.07 (4) CaO 9.86 (49) 0.13 (11) 20.6 (11) 1.08 (9) 11.3 (1) Na 2 O 5.63 (23) 0.20 (4) 0.02 (1) 2.12 (3) K 2 O 0.46 (7) 1.15 (30) Cl 1.68 (49) H 2 O 1.35 (19) Total a Numbers in parentheses represent one sigma variance in averaged analysis in terms of the least figure cited. b Cpx, clinopyroxene; Opx, orthopyroxene. c Total Fe as Fe 2+. right-rear wheel. Although all of these particles, in the presence of a vacuum, would fall back toward the Moon at the same speed, it is obvious that finer particles would be thrown farther and so had longer to travel back to the surface or the BSLSS unit. This could have resulted in a certain particle-size window being preferentially deposited as the LRV traveled through the regolith cloud. Furthermore, vibration during travel of the LRV would have caused the larger particles (e.g., plagioclase mineral fragments) to rise to the top of the sample, as the smaller particles packed tighter beneath them. Finally, the Northern Massif was visited during the third and final EVA, and so it is only natural that material from this area should be abundant at the top of the pile, hence resulting in its preferential gathering when was scooped into a sample bag. The unusual particle-size distribution of the resulting sample is clear evidence that is not a bona fide lunar soil. Yet, it is composed of fragments of lunar soil and as such, has engineering and chemical properties that make it of value for ISRU investigations. [21] Our analysis of JSC-1A matches, within error, that conducted by the USGS (Table 1). Our analysis of JSC-1Af, however, differs from bulk JSC-1A in that it is higher in SiO 2 and CaO and lower in MgO and FeO content. This is possibly due to the preferential finer grinding of plagioclase during the milling process, a function of mineral crushability. Hence the mineral modal distribution of this smaller fraction should differ from that of bulk JSC-1A. It is important that these differences within a simulant are noted, as research utilizing different size fractions may otherwise return unexpected, conflicting, and/or confusing results. [22] Lunar soil simulants cannot reproduce many of the special characteristics of lunar soil, for example, presence of agglutinitic glass and of np-fe 0. Hence work by our group [Liu et al., 2007] has been concerned with producing a simulant additive with the correct distribution of np-fe 0 particles, so as to simulate lunar agglutinitic glass. In addition, it cannot be expected that a simulant, produced from a terrestrial rock, will exactly reproduce the mineral and bulk chemistry of a lunar soil which formed under very different conditions (e.g., low f O 2, lack of H 2 O, vacuum). MLS-1A and JSC-1A were chosen because of certain characteristics that resemble those of lunar soil. JSC-1A consists of a large proportion of glass shards and angular grains that approach the abrasiveness and interlocking characteristics of lunar soil. It is this glass that gives JSC- 1A the suitable engineering and geotechnical properties. Chemically, it is a misfit for most lunar soils, with 10 wt% FeO putting it about half-way between lunar mare (>15 wt%) and lunar highlands (5 wt%) in FeO content (Figures 6a and 6b). A note of caution as concerns chemical similarities however, as the TiO 2 present in JSC-1A is mainly in Ti-magnetite and not in ilmenite, as would be expected from a lunar soil. One of the most prominent chemical differences between the simulants and any lunar soil is that terrestrial rocks and minerals have a large proportion of their iron as Fe 3+, in addition to Fe 2+, whereas on the Moon there is only Fe 2+ or metallic Fe 0. Another often ignored difference is the presence of H 2 O in the lunar soil simulants, commonly present in weathering products such as clays. These differences are significant for processes involving, for example, the production of lunar oxygen. Table 6. Composition of Glass and Major Mineral Phases in JSC- 1A a Glass Plagioclase Olivine Ti-magnetite Cr-spinel SiO (5) 50.0 (1) 38.5 (3) 0.18 (8) 0.22 (17) TiO (17) 10.9 (5) 0.94 (2) Al2O (3) 30.6 (4) 0.04 (1) 9.16 (104) 34.5 (1) Cr 2 O (31) 20.0 (3) V 2 O (5) Fe 2 O (6) 12.1 (1) FeO 12.1 b (5) 0.78 (13) 17.9 (3) 33.0 (7) 16.1 (1) MgO 5.60 (37) 0.15 (2) 42.8 (4) 5.97 (17) 14.0 (1) MnO 0.21 (2) 0.30 (3) 0.32 (3) 0.20 (1) NiO 0.15 (5) CaO 10.5 (6) 14.4 (5) 0.29 (3) 0.16 (2) 0.13 (3) Na 2 O 3.89 (27) 3.15 (24) K 2 O 1.17 (10) 0.13 (3) P 2 O (6) Total a Numbers in parentheses represent one sigma variance in averaged analysis in terms of the least figure cited. b Total Fe as Fe 2+. 8of11

9 Figure 6. Chemical trend plots for soil 70051, lunar simulants, Apollo 17 samples (high Ti and low Ti from Rose et al. [1974]; S Massif, N Massif, and Valley floor from Rhodes et al. [1974]). (a) FeO/Al 2 O 3 concentrations for lunar soils define a decreasing trend from the high-ti mare soils to highland soils. Sample approximates soils from the North Massif. JSC-1A and JSC-1Af show similarities with the Apollo 14 compositions and compositions from the North Massif. MLS-1A shows an affinity with mare compositions and in particular, with samples from the Apollo 17 Valley floor. (b) TiO 2 /Al 2 O 3 plots show Apollo 17 soils trend between the compositions of basalt and anorthositic gabbros collected. Sample has high affinity with North Massif soils. The high concentration of TiO 2 in MLS-1A closely matches those concentrations of Apollo 17 mare soils. Lack of np-fe 0 in the simulants is particularly relevant to reactions involving the application of microwave radiation to heating or melting of the lunar soil [e.g., Taylor and Meek, 2005], and to the magnetic properties of the simulant, which are of importance for studies involving dust mitigation [Taylor et al., 2005]. [23] Chemical differences between simulants and between simulants and the lunar soils they attempt to mimic are not simply due to difference in the valence states of elements but are also a reflection of differences in the compositions of the different mineral phases present. Lunar plagioclases are more anorthositic than their terrestrial counterparts 9of11

10 (Figure 3). Of the simulants, MLS-1A contains the more alkalic plagioclase compositions with 5.63 wt% Na 2 O and 0.46 wt% K 2 O, versus 0.59 wt% Na 2 O and 0.08 wt% K 2 O for plagioclase in JSC-1A best approximates the compositions of olivines with compositions for MLS-1A being more Fe-rich. Further mineralogical differences are evident from the range of pyroxenes present. Those for span almost the entire spectrum of pyroxene compositions, from augite to pigeonite, and Fe-rich pigeonite. Pyroxene compositions for MLS-1A and JSC-1A are more constrained, with MLS-1A containing augite and bronzite (orthopyroxene), and JSC-1A containing augite. 6. Concluding Remarks [24] Among the many processes being evaluated for ISRU on the Moon, the production of LLOX (lunar liquid oxygen) and the recovery of solar-wind implanted particles (e.g., H, He, N, C) rank as priorities. Over 20 processes have been proposed for the production of lunar oxygen [Taylor and Carrier, 1992]. These range from molten silicate electrolysis to hydrogen, and carbothermal reduction. Obviously, experimentation of such processes using real lunar soil is not feasible, so we must use lunar soil simulants such as JSC-1A and JSC-1Af. Once the chosen method has been matured, limited experimentation using lunar soil may be necessary to perfect it. Despite not being a true lunar soil, is composed of portions of lunar soils and as such reflects their chemical composition and engineering properties. Since it lacks the scientific integrity that makes lunar soils so precious to scientists, it is an ideal material for the fine tuning of ISRU processes by engineers. In fact, has previously been used for studies involving topics as varied as the release of noble gases from soils [Bogard et al., 1974]; shock compression by meteorites [Ahrens and Cole, 1974]; solar wind and micrometeorite alteration [Housley et al., 1974]; wave-velocity propagation [Talwani et al., 1974]; noble gases in breccias [Hintenberger et al., 1975]; chemical composition of agglutinates in lunar soil [Rhodes et al., 1975]; Fe-Ti reflectance spectra [Osborne et al., 1978]; dust mitigation [Taylor et al., 2005]; and microwave reactivity [Taylor and Meek, 2005]. Therefore this relatively abundant (1.4 kg) lunar sample, although a degraded sample of the Apollo 17 soil, already has a pedigree in chemical and engineering studies of lunar soils. [25] Processes under consideration for lunar ISRU require the use of simulants to replicate the special qualities of lunar soil. The differences encountered between the simulants described here, however, make it evident that no one material will reproduce all the characteristics required (e.g., chemistry, mineralogy, glass content, np-fe 0 ) for any one given soil, or be suitable for all ISRU processes under consideration. For example, MLS-1A is suitable for studies in which high ilmenite content is a consideration, but not for studying engineering processes. The natural high-glass content of JSC-1A, combined with its particle size distribution, results in this simulant approximating the engineering properties of lunar soil. As such, JSC-1A and JSC-1Af are better suited to studies dealing with dust adhesion/abrasion, regolith handling, excavation, drilling, etc. Detailed knowledge of the composition and properties of lunar soil, and of lunar soil simulants, is essential for the correct development of the ISRU processes that will be implemented on the Moon for long-term human presence in space. [26] Acknowledgments. We would like to thank James Carter for providing a sample of the JSC-1A raw material and a supply of JSC-1Af. Thanks go to James Day for helpful comments during the production of this manuscript and to Allan Patchen for his endless support during electron probe analysis. Thanks are also extended to Carlton Allen and Paul Spudis for helpful comments and reviews of the original manuscript. A portion of this research was supported by a NASA Exploration Systems Mission Directorate contract to L. A. T. Additional financial support was provided by the Planetary Geosciences Institute at the University of Tennessee. References Ahrens, T. J., and D. M. Cole (1974), Shock compression and adiabatic release of lunar fines from Apollo 17, Proc. Lunar Sci. Conf., 5th, Bogard, D. D., W. C. Hirsch, and L. E. Nyquist (1974), Noble gases in Apollo 17 fines: Mass fractionation effects in trapped Xe and Kr, Proc. Lunar Sci. Conf., 5th, Hintenberger, H., L. Schultz, and H. W. 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11 Taylor, L. A., H. Schmitt, W. Carrier, and M. Nakagawa (2005), Lunar dust problem: From liability to asset, paper presented at First Space Exploration Conference: Continuing the Voyage of Discovery, Am. Inst. of Aeronaut. and Astronaut., Orlando, Fla. Tucker, D. S., E. Ethridge, and P. Curreri (1992), Glass fiber processing for the Moon/Mars program, NASA Tech. Memo., NASA TM Weiblen, P. W., and G. B. Morey (1980), A summary of the stratigraphy, petrology, and structure of the Duluth complex, Am. J. Sci., 280-A, Weiblen, P. W., M. J. Murawa, and K. J. Reid (1990), Preparation of simulants for lunar surface materials, in Engineering, Construction, and Operations in Space II, vol. 1, edited by S. W. Johnson and S. P. Wetzel, pp , Am. Soc. of Civ. Eng., Reston, Va. B. Deane, E. Hill, Y. Liu, M. J. Mellin, and L. A. Taylor, Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, TN , USA. (ehill10@utk.edu) 11 of 11