Lunar Regolith Research Articles

Study on Mechanical Properties of QH-E Lunar Soil Simulant under Conventional Triaxial and Cyclic Triaxial Tests

Study of the mechanical properties of lunar soil simulant is the key to conducting lunar soil sampling and lunar base construction. In this paper, conventional and cyclic triaxial tests are performed by using discrete element method (DEM) to study the mechanical properties of QH-E lunar soil simulant. The results indicate that the confining pressure has an important impact on the shear strength and dynamic modulus of QH-E lunar soil simulant. In the conventional triaxial test, with the increasing of the confining pressure, both the peak deviatoric stress and residual stress increase, and the relevant results have been supported by experiments. In cyclic triaxial test, the area of cyclic hysteresis loop decreases with the increasing of the number of cycles, the axial strain and dynamic modulus first increase and then tend to be stable with the increasing of the number of cycles. Moreover, the axial strain increases with increasing confining pressure, while dynamic modulus decreases at a specific cyclic stress ratio (CSR) condition.

Simulation study of the lunar water ice detection based on a small neutron generator

Lunar water ice is an important resource to support the construction of lunar base and other deep space activities, and it is crucial to detect lunar water ice. In this paper, we studied the detection of lunar water ice based on a small neutron generator through Monte-Carlo simulation. The schematic of the detection system and the principle are explained. The simulation results demonstrate that the change of thermal neutron flux with the increase of water content is most obvious and clear. There is a positive correlation between thermal neutron counting and water content in lunar soil. Using thermal neutron counting, the water content can be obtained by inversion.

A Microphysical Thermal Model for the Lunar Regolith: Investigating the Latitudinal Dependence of Regolith Properties

AbstractThe microphysical structure of the lunar regolith provides information on the geologic history of the Moon. We used remote sensing measurements of thermal emission and a thermophysical model to determine the microphysical properties of the lunar regolith. We expand upon previous investigations by developing a microphysical thermal model, which more directly simulates regolith properties, such as grain size and volume filling factor. The modeled temperatures are matched with surface temperatures measured by the Diviner Lunar Radiometer Experiment on board the Lunar Reconnaissance Orbiter. The maria and highlands are investigated separately and characterized in the model by a difference in albedo and grain density. We find similar regolith temperatures for both terrains, which can be well described by similar volume filling factor profiles and mean grain sizes obtained from returned Apollo samples. We also investigate a significantly lower thermal conductivity for highlands, which formally also gives a very good solution, but in a parameter range that is well outside the Apollo data. We then study the latitudinal dependence of regolith properties up to ±80° latitude. When assuming constant regolith properties, we find that a variation of the solar incidence‐dependent albedo can reduce the initially observed latitudinal gradient between model and Diviner measurements significantly. A better match between measurements and model can be achieved by a variation in intrinsic regolith properties with a decrease in bulk density with increasing latitude. We find that a variation in grain size alone cannot explain the Diviner measurements at higher latitudes.

Legal challenges of additive manufacturing on the Moon

Additive manufacturing (AM) is promising for supporting sustainable human presence on the Moon as it reduces costs and dependency on the Earth. It has been incorporated into several lunar programs. Nonetheless, AM on the Moon is legally challenging. First, the legal field most challenged by AM is intellectual property (IP) law, and the peculiar location of AM on the Moon complicates the issue. Deciding the State to exercise jurisdiction and extend its IP protection to the Moon encounters difficulties. Second, AM on the Moon is most valuable when it uses lunar regolith as a source of printing material, which may face similar legal problems to in situ resource utilization, including determining the legality of the activity, deciding the State to exercise the jurisdiction and control over it, the protection of the lunar environment, and so forth. Lunar in situ AM using lunar regolith (LISAMUR), meaning using lunar regolith as raw materials to manufacture objects on the Moon through AM technologies, renders these problems more imminent and substantial. The article delves into the two categories of legal issues ignited by AM on the Moon and reveals that three reasons lead to the legal dilemma: the ambiguous terminology of the space treaties, the abstract principles, and the lacunae in space law. It suggests that as international legislation is slow, temporary approaches of coordinating the understanding of critical notions and relevant principles in space law and updating the registration regime through international cooperation on multilateral platforms would be more viable for coping with the legal challenges of AM on the Moon.

Effect of struvite on the growth of green beans on Mars and Moon regolith simulants

Abstract When humans are going to live on the Moon or Mars, food production and reusing waste products as manure will be essential for their survival. This calls for a circular sustainable agricultural ecosystem for food production. Earlier experiments have shown that crop growth is possible on simulant regoliths though there are several challenges. One of them is the shortage of nitrate or ammonium in the regoliths. Moreover, phosphate is not easily available. This could be solved by the application of human feces as manure. The goal of this experiment was to test if human urine-based struvite (MgNH4PO4) could fertilize Mars and Moon regolith simulants and lead to a higher yield of green beans. Three “soils” were examined: Mars regolith simulant (MMS), Moon regolith simulant (JSC 1A), and Earth potting soil with and without struvite. Forty grams of struvite were added, besides 10% (volume) organic matter. The experiment was conducted in tenfold. Length of plants was recorded, and beans were harvested when ripe and at the end of the experiment, three and a half months after the start. The struvite treatment yielded a significantly higher bean harvest. Plants on potting soil and Moon soil simulant with struvite addition reached the same height and were higher than the control plants. The plants on Mars soil simulant were smaller but still taller than the control. It can be concluded that the addition of struvite had a significant positive effect on the production of green beans on potting soil and Mars and Moon soil simulant.

The Moon as an effective propellant source: A comprehensive exergy analysis from extraction to depot

Establishing a permanent lunar base has gained increasing attention since it offers opportunities for international cooperation and the commercialization of space, forming the foundation and testing ground for a human existence independent from Earth. Essential to future missions beyond cislunar space is the exploration and in situ processing of the Moon's resources, especially the sustainable production of energetic resources and propellants. Utilizing in situ generated propellants can dramatically reduce transportation costs by removing the need to source propellants from Earth. Resources on the Moon are limited, and the extraction of available resources are energy-intensive processes demanding advanced techniques and technologies. Consequently, one of the biggest challenges lies in developing process architectures with a positive energy balance, for which comprehensive analyses are still missing. The focus currently lies on the extraction of water ice from lunar regolith and the production of hydrogen and oxygen through water electrolysis. However, alternative fuel and process options may reduce the energy cost while providing equivalent energetic revenue. In the scope of this research, the infrastructure and technologies required for extraction, refining, and storing are assumed to exist in cislunar space; therefore, only the operating cost is considered. Exergy analyses of in situ extraction methods are conducted to investigate whether the required energetic budget allows sustainable implementation. The analysis includes extraction methods and propellant options to reveal the extent to which alternatives to hydrogen are feasible. Exergy analyses determine thermodynamic losses of energy flows giving the ground for process optimization. The exergy destructed represents the margin of improvement within the process architecture and thus reflects the process's thermodynamic and economic value while allowing a more distinct examination of energy use. Assuming the availability of water and carbon dioxide ice in permanently shadowed regions, the analysis shows that choosing methane instead of hydrogen in combination with oxygen as propellants can reduce the required exergy input by up to a third. An example mission allows to directly compare the operating cost of the extraction processes for the different propellant options. The mission entails a spacecraft propelled by a liquid bipropellant engine utilizing the extracted propellant and transporting a payload of the same propellant to a depot located in lunar near-rectilinear halo orbit (NRHO). Although abundant in space, the results suggest that hydrogen may not be the only or even energetically cost-effective resource for developing cislunar and Martian space infrastructures. Likewise, sustainable extraction of propellants suitable for current and future propulsion systems will foster humanity's reach further into the solar system.

The contact force between lunar-based equipment and lunar soil

Lunar-based equipment plays a vital role in the exploration of the moon because it undertakes the tasks of moving, transporting, digging, and so on. In order to control the gait of lunar-based equipment more precisely and guarantee mobile stability, the contact mechanism between its foot and lunar soil is worthy of in-depth study. In this paper, a contact model is proposed to predict the stress, strain, and displacement both on the contact surface and in the lunar soil when the foot is under vertical load. The axial stress in the proposed contact model is verified through the experiment and its accuracy in the lunar equipment is verified through simulation. The error is in a reasonable range and the influence depth of load conforms to the experiment results. This paper provides a relatively accurate model to describe the contact force between the lunar-based equipment's foot and the lunar soil and will promote the research of lunar exploration.

Preliminary study on localized microwave sintering of lunar regolith

The pioneering objective of a permanent outpost on the lunar surface requires the development of technologies for in situ resource utilisation. Consolidation of lunar soil into products is imperative to avoid unaffordable transportation burdens. The paper addresses the feasibility of the Local Microwave Heating effect as a promising technology for sintering lunar regolith based on microwave radiation, with a simple solid-state generator requiring a relatively modest amount of energy. Experiments were conducted using terrestrial simulants with physical and chemical properties similar to those of lunar regolith. Laboratory equipment with a purpose-built microwave actuator was designed and manufactured with “Design for Embarking” in mind. Experiments have demonstrated the feasibility of the proposed technology with a reasonable degree of confidence. Solid artefacts were obtained with proper setting of microwave parameters and appropriate scanning strategy, proving the feasibility of regolith sintering with a localised microwave source A roadmap for future development of the technology has been established.

Low binder content bricks: a regolith-based solution for sustainable surface construction on the Moon

This work proposes a composite construction material made by a blend of lunar regolith and thermoplastic binders in dry powder form. This solution offers advantages over regolith sintering or melting by requiring lower power consumption and simplifying the manufacturing process. However, its sustainability depends on minimizing the content of the binder material. Drawing from validated concepts used on Earth, such as polymeric concrete and compressed Earth bricks, this paper suggests that binder optimization can be achieved by simplifying and streamlining the manufacturing process, targeting parts with predefined shapes. Standardized elements like bricks or tiles ease production and assembly automation, especially when incorporating interlocking features, simplifying the payload concept transition. After drafting the process with a minimum number of basic steps, this work studies the effects of some process parameters to minimize the weight percentage of the matrix while maintaining reasonable mechanical properties. The compressive and the flexural strength are the targets of an orthogonal array Design of Experiment. Through comparison with reference values for civil engineering, the process demonstrates promising results within an organic phase as low as 10 wt%.

Structure and Gait Design of a Lunar Exploration Hexapod Robot Based on Central Pattern Generator Model

To address the challenges of sinking, imbalance, and complex control systems faced by hexapod robots walking on lunar soil, this study develops an umbrella-shaped foot lunar exploration hexapod robot. The overall structure of the robot is designed to mimic the body structure of insects. By incorporating a four-bar linkage mechanism to replace the commonly used naked joints in traditional hexapod robots, the robot reduces the number of degrees of freedom and simplifies control complexity. Additionally, an extension mechanism is added to the robot’s foot, unfolding into an umbrella shape to provide a larger support area, effectively addressing the issue of foot sinking instability during walking. This study adopts and simplifies the Central Pattern Generator (CPG) model to generate stable periodic control signals for the robot’s legs. Precise control of the extension mechanism’s unfolding period is achieved through mapping functions. A joint simulation platform using Solid Works and Matlab is established to analyze the stability of the robot’s walking. Finally, walking experiments are conducted on the prototype, confirming the smooth walking of the lunar exploration hexapod robot. The results indicate that the designed lunar exploration hexapod robot has a reasonable structure, excellent stability in motion, and the CPG control scheme is feasible.

Telomere dynamics and oxidative stress in Arabidopsis grown in lunar regolith simulant.

NASA envisions a future where humans establish a thriving colony on the Moon by 2050. Plants will be essential for this endeavor, but little is known about their adaptation to extraterrestrial bodies. The capacity to grow plants in lunar regolith would represent a major step towards this goal by minimizing the reliance on resources transported from Earth. Recent studies reveal that Arabidopsis thaliana can germinate and grow on genuine lunar regolith as well as on lunar regolith simulant. However, plants arrest in vegetative development and activate a variety of stress response pathways, most notably the oxidative stress response. Telomeres are hotspots for oxidative damage in the genome and a marker of fitness in many organisms. Here we examine A. thaliana growth on a lunar regolith simulant and the impact of this resource on plant physiology and on telomere dynamics, telomerase enzyme activity and genome oxidation. We report that plants successfully set seed and generate a viable second plant generation if the lunar regolith simulant is pre-washed with an antioxidant cocktail. However, plants sustain a higher degree of genome oxidation and decreased biomass relative to conventional Earth soil cultivation. Moreover, telomerase activity substantially declines and telomeres shorten in plants grown in lunar regolith simulant, implying that genome integrity may not be sustainable over the long-term. Overcoming these challenges will be an important goal in ensuring success on the lunar frontier.

Elemental and Sr isotopic compositions of plagioclase as an indicator of lunar source-rock type: Insights from Chang'e 5 plagioclase fragments

Plagioclase is the most abundant mineral in lunar crustal rocks, and its elemental and Sr isotopic compositions vary among different lunar surface rock types, implying that plagioclase fragments in lunar regolith can be used to trace source-rock types. In this study, we measured major- and trace-elemental and RbSr isotopic compositions of plagioclase fragments from lunar soil returned by the Chang'e 5 (CE5) mission. Correlation between Sr and An contents allows the CE5 plagioclase fragments to be divided into three groups: normal-Sr (group A), high-Sr (group B), and low-Sr (group C). The similarity of elemental and RbSr isotopic compositions between plagioclase in groups A and B and plagioclase from CE5 basalt clasts indicates that plagioclase from groups A and B originated from the comminution of local CE5 basalt. Only two of the eighty-two analyzed plagioclases (∼2.4%) are classified as group C and have Sr isotopes that are distinct from those of groups A and B plagioclases, indicating an exotic origin. One group C plagioclase has a high 87Sr/86Sr ratio (0.70242) and content of rare earth elements and might have been derived from the Sharp B or Aristarchus craters, which are enriched in the KREEP component. The other group C plagioclase has much lower 87Sr/86Sr (0.69908) and a moderately high content of An (92.3) indicating an Mg-suite source rock and possible derivation from the Pythagoras crater. This study highlights the applicability of using elemental and Sr isotopic compositions of plagioclase fragments to trace the origin of lunar regolith.

High-pressure minerals and new lunar mineral changesite-(Y) in Chang’e-5 regolith

Forty-five years after the Apollo and Luna missions, China’s Chang’e-5 (CE-5) mission collected ∼1.73 kg of new lunar materials from one of the youngest basalt units on the Moon. The CE-5 lunar samples provide opportunities to address some key scientific questions related to the Moon, including the discovery of high-pressure silica polymorphs (seifertite and stishovite) and a new lunar mineral, changesite-(Y). Seifertite was found to be coexist with stishovite in a silica fragment from CE-5 lunar regolith. This is the first confirmed seifertite in returned lunar samples. Seifertite has two space group symmetries (Pnc2 and Pbcn) and formed from an α-cristobalite-like phase during “cold” compression during a shock event. The aftershock heating process changes some seifertite to stishovite. Thus, this silica fragment records different stages of an impact process, and the peak shock pressure is estimated to be ∼11 to 40 GPa, which is much lower than the pressure condition for coexistence of seifertite and stishovite on the phase diagram. Changesite-(Y), with ideal formula (Ca8Y)□Fe2+(PO4)7 (where □ denotes a vacancy) is the first new lunar mineral to be discovered in CE-5 regolith samples. This newly identified phosphate mineral is in the form of columnar crystals and was found in CE-5 basalt fragments. It contains high concentrations of Y and rare earth elements (REE), reaching up to ∼14 wt. % (Y,REE)2O3. The occurrence of changesite-(Y) marks the late-stage fractional crystallization processes of CE-5 basalts combined with silicate liquid immiscibility. These new findings demonstrate the significance of studies on high-pressure minerals in lunar materials and the special nature of lunar magmatic evolution.

Artificial Space Weathering to Mimic Solar Wind Enhances the Toxicity of Lunar Dust Simulants in Human Lung Cells.

During NASA's Apollo missions, inhalation of dust particles from lunar regolith was identified as a potential occupational hazard for astronauts. These fine particles adhered tightly to spacesuits and were unavoidably brought into the living areas of the spacecraft. Apollo astronauts reported that exposure to the dust caused intense respiratory and ocular irritation. This problem is a potential challenge for the Artemis Program, which aims to return humans to the Moon for extended stays in this decade. Since lunar dust is "weathered" by space radiation, solar wind, and the incessant bombardment of micrometeorites, we investigated whether treatment of lunar regolith simulants to mimic space weathering enhanced their toxicity. Two such simulants were employed in this research, Lunar Mare Simulant-1 (LMS-1), and Lunar Highlands Simulant-1 (LHS-1), which were added to cultures of human lung epithelial cells (A549) to simulate lung exposure to the dusts. In addition to pulverization, previously shown to increase dust toxicity sharply, the simulants were exposed to hydrogen gas at high temperature as a proxy for solar wind exposure. This treatment further increased the toxicity of both simulants, as measured by the disruption of mitochondrial function, and damage to DNA both in mitochondria and in the nucleus. By testing the effects of supplementing the cells with an antioxidant (N-acetylcysteine), we showed that a substantial component of this toxicity arises from free radicals. It remains to be determined to what extent the radicals arise from the dust itself, as opposed to their active generation by inflammatory processes in the treated cells.

The Spectral Characteristics of Lunar Agglutinates: Visible–Near‐Infrared Spectroscopy of Apollo Soil Separates

AbstractThe lunar surface evolves over time due to space weathering, and the visible–near‐infrared spectra of more mature (i.e., heavily weathered) soils are lower in reflectance and steeper in spectral slope (i.e., darker and redder) than their immature counterparts. These spectral changes have traditionally been attributed to the space‐weathered rims of soil grains (and particularly nanophase iron therein). However, understudied thus far is the spectral role of agglutinates—the agglomerates of mineral and lithic fragments, nanophase iron, and glass that are formed by micrometeoroid impacts and are ubiquitous in mature lunar soils. We separated agglutinates and non‐agglutinates from six lunar soils of varying maturity and composition, primarily from the 125–250 μm size fraction, and measured their visible–near‐infrared reflectance spectra. For each soil, the agglutinate spectra are darker, redder, and have weaker absorption bands than the corresponding non‐agglutinate and unsorted soil spectra. Moreover, greater soil maturity corresponds to darker agglutinate spectra with weaker absorption bands. These findings suggest that agglutinates (rather than solely the space‐weathered rims) play an important role in both the darkening and reddening of mature soils—at least for the size fractions examined here. Comparisons with analog soils suggest that high nanophase iron abundance in agglutinates is likely responsible for their low reflectance and spectrally red slope. Additional studies of agglutinates are needed both to more comprehensively characterize their spectral properties (across size fractions and in mixing with non‐agglutinates) and to assess the relative roles of agglutinates and rims in weathering‐associated spectral changes.

Cosmogenic Isotopes in Lunar Soil: Solar Activity and the Exploding of Nearby Supernova

Cosmogenic Isotopes in Lunar Soil: Solar Activity and the Exploding of Nearby Supernova

Research on the Material Performance and Forming Process of Lunar Regolith Simulant

Establishing a safe and sustainable lunar base on the moon is the foundation for human exploration and development activities. Due to the high transportation costs of the Earth Moon space, a large amount of construction materials are difficult to obtain from Earth. Therefore, how to utilize lunar resources for in-situ construction on the lunar surface has become the key challenge for the construction and operation of lunar base. Faced with special lunar simulant materials and extreme lunar environments, lunar construction faces a series of problems and challenges. This article conducted research on lunar regolith simulant and forming process, providing guidance for lunar surface construction.

Electrostatic Dust Analyzer for Dust Transport Measurements on the Lunar Surface

Lunar dust charging and transport is a more than five-decade-old problem. A high-fidelity and flight-qualified Electrostatic Dust Analyzer (EDA) has been developed to measure the charge, velocity, mass (size), and flux of electrostatically lofted dust particles on the lunar surface. Recent laboratory findings have greatly advanced our fundamental understanding of the dust-charging and -lofting mechanisms, providing critical constraints to the design of the EDA instrument. EDA consists of two identical dust trajectory sensor (DTS) units on both ends of the instrument with a deflection field electrode (DFE) unit lying in between. When a dust particle enters the instrument, charge signals induced on four arrays of wire electrodes in the two DTS units determine the total charge of the dust particle and its trajectory passing through the instrument from which the dust velocity vector is measured. The mass (size) is derived from the deflection of the dust trajectory by the DFE. A dust campaign was performed to characterize the instrument’s performance. The results meet or exceed the requirements. EDA has achieved high Technology Readiness Level 6. EDA measurements are important for assessing the dust environment on the lunar surface and its subsequent impact on crew safety and the operation of exploration systems. Additionally, EDA measurements are expected to have important implications for the surface evolution of all airless bodies, including the Moon and asteroids, in the solar system.

Visible and near-infrared spectral results of Chang’E-5 surficial and subsurface soils

Aims. Studies on high-resolution and high-precision laboratory reflectance spectra of the Moon have historically been restricted to the analysis of old Apollo samples (>3.0 Ga). In contrast, studies of young lunar soils have exclusively relied on the analysis of remote sensing spectra. In this study, we present the results of a laboratory spectral investigation of young lunar soils (~2.0 Ga) obtained by the Chang’E-5 (CE-5) mission. Methods. We analyzed surficial and subsurface soils collected through scooped and drilled sampling methods. The laboratory reflectance spectra of the CE-5 soils were compared with those of Apollo soils and orbital spectra. Two methods were employed for maturity inversion. The relationship between the UV-vis color and TiO2 content of young basalts was also investigated. Results. The CE-5 samples exhibit much fresher spectral features, including higher reflectance, deeper absorption depths, and a smaller visible and near-infrared continuum slope (VNCS), compared to pristine regolith. The subsurface soils sampled from a depth of approximately 10 cm exhibit a slightly fresher spectral feature compared to the surficial soils. Our comparison revealed a rapid rate of space weathering at the lunar surface compared to the vertical overturn. Compared to older iron-rich soils, the CE-5 soils have a larger reflectance but similar UV-vis ratios. The UV-vis ratio alone could not accurately predict the TiO2 content of all mare basalts. The CE-5 samples provide a new ground truth for estimating the TiO2 content of young lunar basalts, which have the largest uncertainty in TiO2 content, as estimated from spectral parameters. We find that the samples returned by the CE-5 mission represent disturbed soils and that they exhibit significantly fresher characteristics compared to pristine regolith, a fact that should be kept in mind when using samples as ground truth for remote sensing research.

Proof of Principle of the Lunar Soil Volatile Measuring Instrument on Chang’ e-7: In Situ N Isotopic Analysis of Lunar Soil

The nitrogen isotopic compositions of lunar soil have important implications for the sources of lunar volatiles and even the evolution of the moon. At present, the research on the lunar nitrogen isotopic compositions is mainly based on the lunar meteorites and the samples brought back by the Apollo and Luna missions. However, volatiles adsorbed on the surface of the lunar soil may be lost due to changes in temperature and pressure, as well as vibration and shock effects when the sample is returned. At the same time, in the case of low N content in the sample, since N is the main component of the earth’s atmosphere, it is easily affected by the atmosphere during the analysis process. Therefore, in situ nitrogen isotopic analysis of lunar soil on orbit is necessary to avoid the problems mentioned above and is one of the primary science goals for the Lunar Soil Volatile Measuring instrument on Chang’e-7 spacecraft. After the nitrogen purification procedure, the volatiles in lunar soil that are released through single-step or stepped heating techniques diffuse to the quadrupole mass spectrometer to obtain the N contents and isotopic compositions of the lunar soil. This paper introduces the ground test for N isotopic analysis of lunar soil in orbit according to the Lunar Soil Volatile Measuring Instrument. After long-term repeated measurements, the background and CO-corrected Air-STD 14N/15N ratio is 268.986 ± 4.310 (1SD, n = 35), and the overall reproducibility of measurements is 1.6%. The accuracy of N isotopic compositions is calculated to be better than 5%, which can distinguish different sources of N components in lunar soil.