Previous studies of martian resources focused nearly exclusively on using CO2 from the atmosphere and H2O from near-surface ice or hydrated minerals to create life support consumables, and propellant for ascent vehicles. Where non-volatile mineral resources have been discussed, they have been treated speculatively with little support from the sample collection. Here, I draw on decades’ worth of data from in-situ exploration by rovers and from martian meteorites to assess the potential mineral resources of Mars. This comes at an inflection point between what could be some of the last large robotic missions to Mars, and the beginning of commercialization and crewed missions. I compile the highest concentrations of 83 naturally occurring elements and compare them to typical ore grades on Earth to assess which may be practical to extract and which will need to be supplied from Earth for the foreseeable future. Sample-based studies support probable ore deposits in Gale crater and Jezero crater including Ni-Cu-PGE sulfide deposits, porphyry copper-like deposits, and heavy mineral sands deposits. Possible indicators for these deposit types are compiled and mapped globally using past orbital measurements and compared to locations where water ice resources are known or suspected. Other more speculative deposit types may be found in still-unexplored geologic environments like long-lived hydrothermal systems and highly evolved igneous terrains.

In order to develop technologies to use lunar ice as a resource, it is important to be able to produce representative analogs, or simulants, of icy lunar regolith. Unfortunately, previous work in this area has not been relevant to the lunar environment due to the practice of mixing liquid water with a regolith simulant before freezing. The lunar near subsurface cannot support liquid water due to very low temperatures and pressures, so water ice modification processes are limited to sublimation deposition. In this work, we investigate the microstructure of various icy lunar regolith simulants via micro-CT scans, including pressure sintered (PSS), thermally sintered (TSS), wet mixed, and unsintered. We show that the PSS and TSS samples are microstructurally most similar to each other and exhibit stark differences to the wet mix samples. We found that the presence of liquid water in the sample preparation process drastically altered the microstructure of the samples and identified key features differentiating the lunar-relevant sintering processes from the wet-mixed samples, including differences in total porosity, pore size, ice particle size, and degree of ice-regolith interconnection. These microstructural dissimilarities are caused in large part by the wetting and lubricating behaviors of liquid water. We conclude that because liquid water cannot exist in the lunar near subsurface and has been shown to behave fundamentally differently from sintered samples at the microstructural level, dry-mixed and sintered analogs should be used for lunar technology development, rather than wet-mixed analogs.

Although water ice has been detected by satellite observations near the lunar poles, it is unknown if this ice is simply frost on the Moon's surface or if larger ice deposits exist in the subsurface. If ice is present within the subsurface, it is unknown if this ice exists as loose ice grains or as a cement that binds regolith grains together. To create an economically viable extraction and production plan for lunar water ice resources, we must characterize near-surface ice concentration and distribution at small (<10 m) spatial and depth scales. Geophysical methods that can be deployed on the Moon's surface, such as seismic surveying, could supply some of this information for future lunar mine planning. To improve our understanding of how seismic surveying may detect and characterize subsurface lunar ice, we performed laboratory ultrasonic velocity measurements of lunar regolith simulant with variable amounts of granular and cementing ice. These measurements were performed under variable confining pressure (0.005-0.08 MPa) and constant low temperature (-26 degrees C). We used these measurements to calibrate a rock physics model to predict seismic velocity as a function of porosity, pressure, ice concentration and ice texture. Our results show that seismic velocity increases with ice concentration, and this increase is roughly 20 times higher for cementing ice than for granular ice. Our model can be used in future studies to predict how effective seismic methods may be for detecting and characterizing subsurface lunar ice deposits with varying ice properties and geologic complexity.

Under lunar polar cold traps, volatile molecules within porous regolith may experience temperature and depth dependent slow mobility. Many degraded lunar craters exhibit thick regolith fill based on models of topographic diffusion and observations of fresh and degraded craters. Regolith has a low thermal conductivity relative to megaregolith and may act as a blanket for internal lunar heat flow, leading to increased temperatures at depth. We develop 2D thermal models of fresh and regolith-filled lunar craters over depths of meters to hundreds of meters below the surface. We find that the base of the stability and slow mobility zones migrate upward with regolith fill, which leads to temperatures that may increase the sublimation rate of volatiles at depth. For a notional cold trap crater 1.6 km in diameter and 3.6 billion years old, topographic diffusion fills it with approximately 90 m of regolith, and the regolith fill's blanketing effect causes the 110 K isotherm to shift about 180 m upward. This places it approximately 25 m below the current cold trap surface and well above the initial crater floor. The slow water ice mobility zone below the 110 K isotherms also shifts upward with regolith fill, potentially increasing volatile concentrations at shallower depths. These secondary volatile concentrations may be targets for sampling and testing hypotheses of volatile system processes. In addition, remobilized volatile concentrations may be a resource for future In-Situ Resource Utilization (ISRU) applications. The thick regolith fill in degraded craters and volatile remobilization potential in lunar subsurface cold traps have implications for future exploration instruments, sampling, and ISRU architectures.

With the renewed commitment from NASA and other commercial entities for a presence on the Moon, the importance of understanding the characteristics of lunar regolith and how to utilize it have become the target of increasing scrutiny. Much of what is known about lunar regolith was collected during and immediately after the Apollo program, however, analytical techniques and instrumentation have advanced in leaps and bounds in the subsequent decades. Specifically, dynamic image analysis systems have advanced to the point that millions of particles can have morphological characteristics automatically determined in relatively short time frames. Particle morphological data was collected on several lunar samples and a pair of widely used regolith simulants to ascertain the accuracy of these simulants and to explore statistical analysis methods of these large datasets. It is found that these morphology datasets can vary widely depending on the particle size of the particles, and simple averaging of the data skews the results heavily towards the numerically abundant size ranges, the fines. Different reporting methods are suggested to ameliorate these problems. When applied to the lunar regolith, the particles are noted to be less morphologically complex than initially suspected. Compared to the lunar material, the simulants are found to contain some more morphological variability and angular grains. Such difference is likely due to the wildly different comminution processes that these different powder systems are subjected to.

Seismic methods will be useful for future lunar near-surface characterization, and high-fidelity elastic models will be required to aid interpretation of seismic observations. To develop an elastic lunar near-surface model, we performed ultrasonic velocity measurements of lunar regolith simulant at low confining pressure and developed a rock physics model calibrated to these measurements. Grain contact models based on Hertz-Mindlin theory produce accurate results at high confining pressure (i.e., several hundred meters or more burial depth) but historically fail to predict observed velocities in unconsolidated media at low pressure. Therefore, we heuristically modified existing models to fit our measured data over a range of porosities and confining pressures. To compare with Apollo 14 and 16 active seismic experiments, we used our new heuristic rock physics model to produce lunar subsurface velocity profiles. We performed ray tracing through our velocity profiles to calculate seismic traveltime, which results in good agreement with first arrivals interpreted from the Apollo experiments. Our model suggests a slightly higher velocity-pressure dependence than inferred from in situ measurements, which may be due to porosity reduction in the lunar regolith from impact-induced and natural vibrations. Seismic velocity is the speed at which mechanical waves travel through planetary materials and is controlled by the physical properties of those materials such as density and compressibility. We have created a model that relates seismic velocity to depth and porosity under lunar conditions and have calibrated that model with laboratory measurements of lunar soil simulant at low pressure (i.e., near-surface) conditions. Using this model, we can predict seismic velocity in the lunar subsurface and compare the modeled velocity with observations from Apollo active seismic experiments. Slight differences between our model and Apollo observations may be due to lower porosity in the lunar soil caused by vibrations from asteroid impact events and seismic quakes. We collected ultrasonic velocity measurements of lunar regolith simulant at low confining pressure to calibrate a rock physics model Our rock physics model predicts shallow lunar seismic velocity in agreement with observations from the Apollo active seismic experiments Our model may be used in future studies to predict lunar near-surface seismic velocity under variable resource scenarios

Due to the lack of in-situ geotechnical data from lunar Permanently Shadowed Regions (PSRs), it is important that a versatile icy regolith simulant be used in terrestrial development of rovers, excavators, and water extractors intended for operating in lunar PSRs. Fine tuning of existing icy regolith simulant properties is not possible; for a given water percentage they either exhibit strength similar to high strength concrete or to sand, but nothing in between. In this work we present a novel method for creating icy lunar regolith simulant, called Pressure Sintered icy lunar regolith Simulant. PSS is notable for being created from solid phase water, and for being tailorable to a wide range of mechanical properties through the sintering of ice and regolith grains, induced by applied uniaxial pressure. Samples were produced at 0%, 2%, 5%, and 10% ice content as measured by weight, and were pressed at four different pressure levels. Penetration resistance was measured for each of these samples, and it was observed that a continuous distribution of penetration resistance levels could be achieved by varying the applied pressure and ice content. Significant relaxation of samples during the pressing process was also observed. The production method for PSS is included, and is followed by the penetration resistance and density results along with some qualitative observations. Finally, we make recommendations for the use of PSS in terrestrial testing activities.

Metals and metallic elements in silicate/oxide form are abundant in asteroid materials and are often touted as a valuable space resource that can be returned to Earth or used in space. However, the data that come along with these claims are decades old, incomplete, and of questionable quality. Here, we draw on newer measurements and statistics from the vast meteorite collection to assess the concentrations of many elements in likely asteroid materials compared to terrestrial ore deposits. A cursory comparison of 83 elements identifies a promising group that are examined in more detail: the platinum group metals (PGMs) Rh, Ru, Pd, Os, Ir, Pt, and the base metals Fe, Mg, Al, and Si. PGMs are found to deviate from chondritic ratios with respect to Ir at higher Ir values, such that maximum PGM contents in asteroids likely do not reach as high as previously thought. However, there may be other strategies to form a PGM-rich concentrate, for example separating out refractory metal nuggets from more primitive undifferentiated asteroids. In addition to precious metals, the base metals Fe, Mg, Al, and Si can be chemically reduced and used to support in-space manufacturing, particularly for large space structures and solar panels. In all cases, the path from raw asteroid material to refined products can be organized using the concept of flowsheets from terrestrial mining, where mineral processing/beneficiation is of first-order importance.

Lunar soils will be an important feedstock for multiple space resource utilization applications including preparing sites for infrastructure, extracting metals, and manufacturing products. On Earth, soil classification systems provide a logical way to categorize different soils and are applied in soil surveys for development projects. However, these systems and others used for soil science are not appropriate to translate to the Moon because of fundamental differences in soil properties, especially clay and moisture content. Here, I propose a lunar soil classification system based on practical space resource use cases. The system includes bulk elemental composition and particle size distribution as its main variables to form 9 soil groups and can be extended with tags that represent additional properties like glass content or other mineral/elemental components. The system is designed to be simple to apply: classification criteria can be measured with in-situ instruments as well as remote sensing. Proof of concept maps are developed globally, and the Apollo 17 sample collection is used as ground truth for orbital-derived classifications over the Taurus-Littrow valley. The different soil groups are expected to perform better or poorer for specific use cases. For example, coarse grained soils will have higher flowability and higher compressibility that are important for excavation and conveyance. Mare composition soils will have lower melting points and are enriched in FeO and TiO2 as sources of iron and titanium. Adopting a simple, standardized classification scheme will improve communication between different players for assessing resources, developing and testing hardware, and eventually selling raw and refined lunar materials.

The reaction of lunar minerals to water is understudied. Lunar regolith will generally show a strong reactivity to water, and if lunar minerals are dispersed in water-based liquids, significant mineral dissolution can be expected. Here it is proposed to use lunar regolith covering the Moon surface as a primary feedstock for the production of synthetic phyllosilicates. The envisioned concept suggests dispersing fine-grained regolith in water-based media, which will result in the leaching of ions from the regolith. The leached ions will be separated from the initial leaching solution, followed by precipitation of the ions under steady conditions. The resulting solids are a portfolio of synthetic clays in various polymorphs and shapes with a range of applications in ISRU. Furthermore, the suggested work can be expected to inform research work on regolith/lunar dust in contact with water, such as greenhouses, astrobiology, dust inhalation, lunar water ice, habitat construction, and more.

The Moon???s dusty surface environment threatens any equipment that operates there, especially for long-duration infrastructure needed for a sustained lunar presence. This is doubly true for systems that convey regolith, which by agitating the soil are certain to generate dust. Here, we provide a comprehensive review of technologies that have been proposed to convey regolith on the lunar surface, and to mitigate against dust hazards that are generated by such transport systems. We define functional taxonomies for both regolith conveyance and dust mitigation, then carry out quantitative trade studies in several categories for each. Examples include passive and active dust mitigation, and horizontal and near vertical conveyance. Conveyance technologies that scored particularly high include wheeled haulers, conveyor belts, and auger/hopper transfer points. High scoring dust mitigation technologies include the lotus leaf passive coating, Electrodynamic Dust Shield, and boots or bellow made of fiberglass fabric. We also explore novel or unconventional concepts and describe how dust mitigation and regolith conveyance can be combined using a systems approach with multiple technologies layered together. The results from the trade studies and the subsequent recommendations constitute a practical guide that can be used for designing and developing systems that must perform efficiently and reliably to carry out useful tasks on the Moon or Mars, such as resource extraction, construction, and additive manufacturing.

New SpaceVol. 10, No. 2 EditorialSpace Resources: Leading the Way to a Prosperous FutureKevin M. Cannon, Angel Abbud-Madrid, Christopher Dreyer, and George SowersKevin M. CannonAddress correspondence to: Kevin M. Cannon, Center for Space Resources, Colorado School of Mines, 1310 Maple St., GRL 234, Golden, CO 80401 E-mail Address: [email protected]Space Resources Program, Colorado School of Mines, Golden, Colorado, USA.Department of Geology and Geological Engineering, Colorado School of Mines, Golden, Colorado, USA.Search for more papers by this author, Angel Abbud-MadridSpace Resources Program, Colorado School of Mines, Golden, Colorado, USA.Search for more papers by this author, Christopher DreyerSpace Resources Program, Colorado School of Mines, Golden, Colorado, USA.Search for more papers by this author, and George SowersSpace Resources Program, Colorado School of Mines, Golden, Colorado, USA.Search for more papers by this authorPublished Online:12 May 2022https://doi.org/10.1089/space.2022.29042.kmcAboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View article"Space Resources: Leading the Way to a Prosperous Future." New Space, 10(2), pp. 113–114FiguresReferencesRelatedDetails Volume 10Issue 2Jun 2022 InformationCopyright 2022, Mary Ann Liebert, Inc., publishersTo cite this article:Kevin M. Cannon, Angel Abbud-Madrid, Christopher Dreyer, and George Sowers.Space Resources: Leading the Way to a Prosperous Future.New Space.Jun 2022.113-114.http://doi.org/10.1089/space.2022.29042.kmcPublished in Volume: 10 Issue 2: May 12, 2022Online Ahead of Print:March 11, 2022PDF download

Scientific exploration of extraterrestrial planets has gripped human imagination since the advent of space travel. Human missions to Mars could produce insight into the essential questions of how, when and where life began on Earth. Such missions would only be feasible using local space resources materials, a concept called in situ resource utilization (ISRU). In the absence of organic materials from plants, the globally available oxidic surface minerals (regolith) are the only viable resource for large-scale construction efforts such as habitats, greenhouses, landing pads and equipment building. This review provides the first comprehensive literature review of ISRU materials research employing Martian simulants. It gives a detailed overview of all Mars simulants, their history, properties, and challenges, introducing a generational concept for simulants development. The available Mars simulant processing literature (including selected work on lunar simulants) is categorized into seven regolith bonding concepts. The state-of-the-art on additive manufacturing (AM) in ISRU research is discussed. Detailed feasibility assessments for all processing approaches are given, including overview graphs comparing the mechanical performance of each fusion concept with feedstock availability on the surface of Mars. Finally, major open questions and future challenges of materials processing for early Mars missions is examined.

We analyze the surface roughness of five north polar craters on Mercury using 125 m/pixel Mercury Laser Altimeter data. Each crater hosts a polar deposit (PD) with a low‐reflectance surface. The PDs have distinct geologic contacts, enabling an analysis of roughness across deposit boundaries onto ice‐free portions of the host craters' floors. The low‐reflectance surfaces in Angelou, Despréz, and Ensor collocate with radar‐bright signatures consistent with the presence of several‐meters‐thick water‐ice deposits beneath their low‐reflectance surfaces. Subdued roughness in these three craters is consistent with the superposition of several meters of ice. The difference between roughness on and off their low‐reflectance surfaces is within one standard deviation (SD) of the results, but is found to be statistically significant, as indicated by K‐S and Mann‐U Whitney tests, and meaningful, as indicated by Cohen's d tests. There is no meaningful difference in Jiménez and Josetsu, two craters that lack strong radar‐bright signatures, consistent with the hypothesis that they do not host substantial water ice beneath their low‐reflectance surfaces and thus not all of Mercury's available cold traps are occupied by water ice. Analyzing the roughness of polar craters may provide insight into the presence/absence of thick volatile deposits, but higher‐resolution topography would be helpful given the high SD associated with roughness. Finally, we identify subdued roughness along three PDs that may be related to thick lag deposit margins or enhanced diffusive mixing along deposit edges. Roughness may provide new insight into surface characteristics of the ices and inform surface evolution models.

We designed a laboratory visible-to-near-infrared (VNIR) hyperspectral experiment to test the effectiveness of factor analysis/target transformation for detecting minerals mixed with Mars Global Simulant-1 (MGS-1). The purpose of this experiment is to test for true positive, true negative, false positive, and false negative results from application of factor analysis/target transformation methods and determine the parameters that dictate good versus bad algorithm performance. Gypsum, calcite, montmorillonite, nontronite, and kaolinite were each mixed with MGS-1 at abundances of 1%, 2.5%, 5%, 10%, 20%, and 50%. The mixtures were placed in 2.5 x 2.5 x 1 cm sample trays and imaged using a Headwall Imaging Spectrometer with a spectral range of 0.9-2.6 mu m, 8.98 nm spectral sampling, and 0.34 mm/pixel spatial resolution. These images include thousands to tens of thousands of hyperspectral pixels covering each individual mixture tray. Full-image factor analysis/target transformation (FA/TT) and Dynamic Aperture Factor Analysis/Target Transformation (DAFA/TT) were applied to these data to detect the minerals mixed with MGS-1. The results demonstrate that factor analysis/target transformation is prone to both false positive and false negative detections, but in certain applications-including DAFA/TT-it can be useful for highlighting spectrally interesting areas in hyperspectral images for follow-up investigation. The results presented here demonstrate that applications of factor analysis/target transformation to VNIR hyperspectral datasets should be used to highlight small outcrops and/or weak spectral signals in pixels for follow-up investigation. This emphasizes the need for supporting evidence to be obtained-in addition to factor analysis/target transformation-before interpretations of planetary surface processes should be made.