Lunar Regolith Simulant Research Articles

Experimental study on particles directed transport by an alternating travelling-wave electrostatic field

A continuous and controllable lunar regolith directed transport is crucial for the development of the 3D printing technology on the moon. The electrostatic method becomes a promising particle transport method for the extraterrestrial environment due to its irreplaceable advantages over other traditional methods. In this paper, particle directed transport by an alternating four-phase travelling-wave electrostatic field is experimentally investigated. Great efforts are made to carefully present the detailed particle movement trajectories and to deeply understand the particle control mechanism of the electrostatic method. It is found that not only the excitation frequency would affect the particles' transport direction, but also the voltage amplitude and geometric parameters would change the transport direction. For the present experiments, the backward transport of lunar regolith simulant can be realized at the low frequency conditions (2– 30 Hz). By post-processing of the recorded pictures, the detailed particle behaviors and the changes of the particles' velocity vector distribution with the electrostatic field propagation are obtained. The formation processes of both the forward and backward directed transports of particles are carefully demonstrated and discussed. Based on the obtained results, the most important part of particles, which plays a great role in the directed transport formation in an alternating electrostatic field, is determined and valuable investigation suggestion is proposed. Additionally, the impacts of the key influencing parameters on particle transport performance are obtained.

Bioweathering improvement of lunar soil simulant improves the cultivated wheat's seedling length

Crewed base is the future trend of lunar exploration. Bioregenerative life support system (BLSS) is necessary for crewed lunar bases, with plant cultivation as the core functional unit. Since transport from the Earth to the Moon is expensive, BLSS should make full use of in situ resources. Lunar soil is the most abundant in situ resource on lunar surface and has little biological toxicity, which could be used as the substrate of plant cultivation in BLSS. However, never experiencing bioweathering process as the Earth's soil, lunar soil has sharp particles at the micro level and thus poor porosity (i.e. poor water holding and aeration capacities) at the macro level. That is, lunar soil's bioavailability for plant cultivation needs to be improved. Imitating bioweathering process, we mixed and co-fermented lunar soil simulant with organic solid waste (composed of plant residues, human feces and microbes) generated by BLSS to improve the bioavailability. Results show that, indicated by the cultivated wheat's seedling length, the bioavailability of lunar soil simulant was significantly (P < 0.05) improved by solid waste and further by fermentation, but optimal solid waste content should be below 0.5% of lunar soil simulant (dry w/w). The significantly (P < 0.05) enriched Na+ during the fermentation was probably released from lunar soil simulant, indicating a successful bioweathering corrosion on lunar soil particles. Consistently, multiple abundant microbial genera reported as able to corrode lunar soil's chemical components were found in the improved substrate. Since the real lunar soil is chemically similar to its simulant, sharp particles of real lunar soil could also be corroded by bioweathering improvement to prevent plant root injury at the micro level, as well as to improve the substrate's porosity at the macro level. This study brings confidence to future lunar soil utilization programs.

Lower temperature electrochemical reduction of lunar regolith simulants in molten salts

Extraction of oxygen from lunar soil is key to the sustainability of human and robotic operations on the Moon and would open the path to in-space refuelling with space resources. This work investigates reducing the temperature of the electrochemical FFC process, by changing the salt from pure CaCl2 to eutectic mixtures with KCl, NaCl and LiCl. Initial experimental results demonstrate the feasibility of removing at least 40% of the oxygen present in lunar minerals in 24 ​h in all eutectics and at temperatures as low as 660 ​°C; 85% of the oxygen could be removed in the comparative experiment using the baseline conditions of CaCl2 at 950 ​°C. Besides the expected impact on the kinetics when running the process at lower temperature, parasitic reactions linked to the graphite anode's interaction with the extracted oxygen, calcium cycling between the electrodes, and other mechanisms specific to each salt mixture appear to have a significant impact on the reduction process. Further work is needed to understand the limiting factors for the reduction in each eutectic salt electrolyte.

Preparation of geopolymer based on lunar regolith simulant at in-situ lunar temperature and its durability under lunar high and cryogenic temperature

Lunar base construction is of great importance for deep space exploration, and the establishment of lunar pavements for the movement of machinery and transportation of materials is essential to improve construction efficiency. Lunar regolith as an in-situ resource has been demonstrated to be used as raw materials to prepare geopolymers for lunar pavements. In this paper, geopolymers based on lunar regolith simulant with different concentrations of alkali activator were synthesized using the natural high-temperature of the lunar surface. Then, the durability of the resulting geopolymer under lunar high and cryogenic temperature was investigated. The flexural and compressive strength was tested, and the microstructure was characterized using Scanning Electron Microscope coupled with Energy Dispersive Spectroscopy (SEM-EDS), 29Si Magic Angle Spinning-Nuclear Magnetic Resonance (29Si MAS-NMR), and Mercury Intrusion Porosimetry (MIP). The results of the curing section showed that the geopolymer with 8 mol/L sodium hydroxide (NaOH) generated high strength and dense structure, and the period of 420 h–492 h of a lunar day corresponding to a temperature variation from 84.5 °C to 33.5 °C in 72 h was suitable for preparation, with 5.7 MPa and 31.2 MPa 72-h flexural and compressive strength. Three test points were selected on the lunar 30° latitude temperature curve, corresponding to before and after the cryogenic attack, and after high temperature again to investigate the durability of the geopolymer, and the degradation was found noticeable. The flexural strength decreased about 49% and 70%, and the compressive strength decreased about 15% and 18% after the cryogenic temperature and high temperature again, respectively. Microscopic observations revealed that the geopolymer structure was significantly granulated with obvious cracks and increased porosity. In addition, the formation of the zeolitic phase was unexpectedly found, leading to interfacial cracks and mechanical strength reduction of the geopolymer. This paper will be beneficial to explore the evolution of properties of lunar pavement construction materials in the lunar environment.

A data-driven deep learning model of radiative heat transfer in dense granular systems

Radiative heat transfer has attracted increasing research interest in various dense granular systems, including large-scale nuclear pebble-bed reactors, fusion breeder blankets, packed beds, metal powder beds and granular lunar regolith simulants. The optimised ray tracing method (ORTM) with a Sobol quasi-random sequence is proposed to calculate the obstructed view factor between spheres, and it converges much faster than that with the traditional pseudorandom number sampling method. Based on discrete particle packing of nuclear pebble bed HTR-PM and random particle generation, a large obstructed view factor dataset of thermal radiation is generated by parallel CUDA computing for training a deep learning regression model to discuss the packing-property linkage for radiative heat transfer in the large-scale particle bed. Compared with other approaches, the deep residual neural network (ResNet) with the swish activation function applied in this paper is found to be the best neural network architecture for view factor prediction without vanishing gradients or model degradation problems during training. The testing error of the trained deep learning model is <1.0 × 10-4 for over 99.96% view-factor cases in nuclear pebble beds, and it has proven to be 7.3 × 105 times faster than the traditional numerical method in view-factor calculations. This makes it feasible to explore the local and macroscopic thermal radiation behaviours in large-scale pebble beds filled with up to 1.0 × 107 spheres.

Development of a New Pressure-Sinkage Model for Rover Wheel-Lunar Soil Interaction based on Dimensional Analysis and Bevameter Tests

A rover is a planetary surface exploration device designed to move across the ground on a planet or a planetary-like body. Exploration rovers are increasingly becoming a vital part of the search for scientific evidence and discoveries on a planetary satellite of the Sun, such as the Moon or Mars. Reliable behavior and predictable locomotion of a rover is important. Understanding soil behavior and its interaction with rover wheels—the terramechanics—is of great importance in rover exploration performance. Up to now, many researchers have adopted Bekker’s semiempirical model to predict rover wheelsoil interaction, which is based on the assumption that soil is deformable when a pressure is applied to it. Despite this basic assumption of the model, the pressure-sinkage relation is not fully understood, and it continues to present challenges for rover designers. This article presents a new pressure-sinkage model based on dimensional analysis (DA) and results of bevameter tests. DA was applied to the test results in order to propose a new pressure-sinkage model by reducing physical quantitative parameters. As part of the work, a new bevameter was designed and built so that it could be successfully used to obtain a proper pressure-sinkage relation of Korean Lunar Soil Simulant (KLS-1). The new pressure-sinkage model was constructed by using three different sizes of flat plate diameters of the bevameter. The newly proposed model was compared successfully with other models for validation purposes.

Study of the rheology of lunar regolith simulant and water slurries for geopolymer applications on the Moon

To reduce transportation costs for building a lunar base station, it is important to utilise in-situ resources like lunar regolith. Lunar regolith can be used to create a concrete-like material by means of geopolymerization. For application of geopolymerizing mixtures, the rheology of the slurry must be known in advance. This article investigates the rheology of mixtures of lunar dust simulants with water, NaOH (as alkaline agent) and urea (as superplasticizer). The rheology of all the mixtures can be approximated with the Bingham Model. Aging has a dramatic effect on the rheology of the water + simulant mixture and, after 2 days, the yield stress decreases by six times. The presence of NaOH, on the contrary, increases both the apparent viscosity and the yield stress as it promotes geopolymerization. The addition of urea reduces the viscosity by 25%, but it has a limited effect on the yield stress. These findings can enable the design of construction 3D printers on the moon.

Influence of lunar regolith compressibility on sampling performance of thick wall spiral drills

A 2 m class robotic drill was sent to the Moon and successfully collected and returned regolith samples in late 2020 by China. It was a typical thick wall spiral drill (TWSD) with a hollow auger containing a complex coring system to retain subsurface regolith samples. Before the robotic drill was launched, a series of laboratory tests were carried out to investigate and predict the possible drilling loads it may encounter in the lunar environment. This work presents how the sampling performance of the TWSD is affected by the regolith compressibility. Experiments and analysis during the drilling and sampling process in a simulated lunar regolith environment were conducted. The compressibility of a typical lunar regolith simulant (LRS) was measured through uni-directional compression tests to study the relationship between its inner regolith stress and bulk density. A theoretical model was established to elucidate the cutting discharge behavior by auger flights based on the aforementioned relationship. Experiments were conducted with the LRS, and the results show that the sampling performance is greatly affected by the flux of the drilled cuttings into the spiral flight channels. This work helped in scheduling reasonable drilling parameters to promote the sampling performance of the robotic drill in the Chinese Chang'E 5 mission.

Potential of Acidithiobacillus ferrooxidans to Grow on and Bioleach Metals from Mars and Lunar Regolith Simulants under Simulated Microgravity Conditions.

The biomining microbes which extract metals from ores that have been applied in mining processes worldwide hold potential for harnessing space resources. Their cell growth and ability to extract metals from extraterrestrial minerals under microgravity environments, however, remains largely unknown. The present study used the model biomining bacterium Acidithiobacillus ferrooxidans to extract metals from lunar and Martian regolith simulants cultivated in a rotating clinostat with matched controls grown under the influence of terrestrial gravity. Analyses included assessments of final cell count, size, morphology, and soluble metal concentrations. Under Earth gravity, with the addition of Fe3+ and H2/CO2, A. ferrooxidans grew in the presence of regolith simulants to a final cell density comparable to controls without regoliths. The simulated microgravity appeared to enable cells to grow to a higher cell density in the presence of lunar regolith simulants. Clinostat cultures of A. ferrooxidans solubilised higher amounts of Si, Mn and Mg from lunar and Martian regolith simulants than abiotic controls. Electron microscopy observations revealed that microgravity stimulated the biosynthesis of intracellular nanoparticles (most likely magnetite) in anaerobically grown A. ferrooxidans cells. These results suggested that A. ferrooxidans has the potential for metal bioleaching and the production of useful nanoparticles in space.

Measurement and calibration of DEM parameters of lunar soil simulant

In this paper, the lunar soil simulant parameters were calibrated using the discrete element method (DEM) for accurate simulation of the interactions between rover wheel and lunar soil simulant. Plackett-Burman, steepest ascent, and Box-Behnken experiments were utilized to propose a parameter calibration methodology. Firstly, the Plackett-Burman experiment was adopted to verify the influences of the nine parameters on the angle of repose (AoR), while three parameters with the most significant effects were identified according to their contributions, and the steepest ascent experiment narrowed their range. Then, the Box-Behnken experiment was utilized for their calibration and obtaining their optimal values. In the simulation, the Hertz–Mindlin (with JKR) contact model was chosen as the contact model. Finally, the calibrated DEM parameters were employed to perform the AoR validation test. The relative error between the simulation and experimental results was 3.4%. The penetration tests were then accomplished further to verify the accuracy and validity of DEM parameters. The penetration resistance curves in the simulation were compatible with the experiment. The obtained results can be utilized for future studies on the interaction between the rover wheel and soil.

Effects of Ilmenite on the Properties of Microwave-Sintered Lunar Regolith Simulant

AbstractMicrowave sintering is regarded as a high-efficiency, energy-saving, and rapid-heating technique for the preparation of structural materials on the Moon. However, the influencing factors (i...

Preparation and characterization of a specialized lunar regolith simulant for use in lunar low gravity simulation

Lunar in-situ resource utilization (ISRU) has been put on the agenda by many countries. Due to the special material nature and low gravity environment, the lunar regolith demonstrates significantly different behavior from terrestrial geomaterials. However, the systematic understanding of its geotechnical behavior is now seriously restricted by the scarcity of lunar regolith and the difficulty in simulating lunar gravity. A new lunar regolith simulant, termed as China University of Mining and Technology Number One (CUMT-1), has been developed to recover properties of the lunar regolith and simulate the lunar gravity by adopting the recently advanced geotechnical magnetic-similitude-gravity model testing (GMMT) method. The CUMT-1 simulant was prepared by reproducing the in-situ formation and fragmentation of the lunar matrix, which plays a key role in the irregular particle morphology. The mineralogical compositions, particle morphology and gradation, specific gravity, bulk density, void ratio, shear strength, and compressibility were determined. After quantifying the magnetization and magnetic-similitude-gravity characteristics, an application of the cone penetration resistance under low gravity was further given. The obtained results are compared to the values known for lunar regolith samples and other simulants, which demonstrates promising characteristics for use in geotechnical engineering-based and scientific-based applications, especially considering the influence of lunar gravity.

Assessment of shear strength and compressibility characteristics of a newly developed lunar highland soil simulant (LSS-ISAC-1) for Chandrayaan lander and rover missions

The engineering properties (shear strength and compressibility) of lunar soils influence the design of landers, rovers, and their mobility behavior on the lunar surface. Assessing such properties is important for any lunar-based studies, and it is usually being determined by using suitable lunar soil simulants. This paper explains the shear strength parameters, stress-strain relationships, and volume change behavior of the newly developed lunar highland soil simulant (LSS-ISAC-1), apart from particle size distribution, which have a profound influence on the engineering behavior. In addition, to the above, other engineering properties such as critical state of the angle of internal friction, dilatancy angle, Young's modulus, Poisson's ratio, internal erodibility, small-strain shear wave velocity, and shear modulus have also been evaluated and presented. Mohr-Coulomb and friction-dilatancy theories are considered as a base for the analysis with the use of statistical predictive equations. The relative density and confining pressures are used as functions in the predictive equation to assess the behavior of the LSS-ISAC-1. The comparison of properties with the actual lunar highland soil samples of the Apollo 16 mission reveals a reasonable similarity of LSS-ISAC-1 with the lunar highland soils.

Reliability and effectiveness of laser scanners in future construction efforts on the Moon and Mars

The exploration and conquest of the Moon and Mars is very likely in the near future. Therefore the erection of lunar and Martian structures, suitable for permanent human presence is increasingly discussed by the scientific community. Various concepts have been proposed for creation of lunar and Martian permanent bases. Techniques ranging from 3D printing of concrete, through utilization of natural caves to inflatable pressurized tensile structures are considered. In authors' opinion a fast, accurate and remote measuring technique will be necessary for successful completion of majority of extra-terrestrial construction tasks. The terrestrial laser scanning technique should be used for the lunar and Martian construction projects. To assess the suitability of terrestrial laser scanning techniques which are going to be used on the Moon and Mars, initial measurements should be conducted on Earth. Unfortunately extra-terrestrial soils are not available for general research. The only feasible solution is to use lunar and Martian soil simulants to practice construction technologies, techniques and strategies. The main aim of this research programme is radiometric and geometric analysis of TLS point clouds collected during the measurement of lunar and Martian soil simulants targets. The conducted research programme was focused on the analysis of a laser beam dispersion and absorption in soil simulants. It should be noted that the dispersion and absorption of a laser beam for the scanned surface is a key factor in TLS remote measurements. The advantages and limitations of TLS technique for possible lunar and Martian applications was discussed. Areas of subsequent research were pointed out. In the first section the brief state-of-the-art was given in context of the conducted research programme. Subsequently, in section two used specimens and equipment was described. The third section of the paper was dedicated to present the conducted research programme. The achieved results were shown in section four in the form of tables and graphs. Finally, in section five the discussion was carried out and followed by a list of drawn conclusions. It was proved that TLS technique can be used to effectively scan LSS and MSS, thus scanning on the Moon and Mars is enabled.

Additive Manufacturing and Spark Plasma Sintering of Lunar Regolith for Functionally Graded Materials

This study investigates the feasibility of in-situ manufacturing of a functionally graded metallic-regolith. To fabricate the gradient, digital light processing, an additive manufacturing technique, and spark plasma sintering were selected due to their compatibility with metallic-ceramic processing in a space environment. The chosen methods were first assessed for their ability to effectively consolidate regolith alone, before progressing regolith directly onto metallic substrates. Optimized processing conditions based on the sintering temperature, initial powder particle size, and different compositions of the lunar regolith powders were identified. Experiments have successfully proven the consolidation of lunar regolith simulants at 1050°C under 80 MPa with digital light processing and spark plasma sintering, while the metallic powders can be fully densified at relatively low temperatures and a pressure of 50 MPa with spark plasma sintering. Furthermore, the lunar regolith and Ti6Al4V gradient was proven to be the most promising combination. While the current study showed that it is feasible to manufacture a functionally graded metallic-regolith, further developments of a fully optimized method have the potential to produce tailored, high-performance materials in an off-earth manufacturing setting for the production of aerospace, robotic, or architectural components.

Blood, sweat, and tears: extraterrestrial regolith biocomposites with in vivo binders.

The proverbial phrase ‘you can’t get blood from a stone’ is used to describe a task that is practically impossible regardless of how much force or effort is exerted. This phrase is well-suited to humanity’s first crewed mission to Mars, which will likely be the most difficult and technologically challenging human endeavor ever undertaken. The high cost and significant time delay associated with delivering payloads to the Martian surface means that exploitation of resources in situ — including inorganic rock and dust (regolith), water deposits, and atmospheric gases — will be an important part of any crewed mission to the Red Planet. Yet there is one significant, but chronically overlooked, source of natural resources that will — by definition — also be available on any crewed mission to Mars: the crew themselves. In this work, we explore the use of human serum albumin (HSA) — a common protein obtained from blood plasma — as a binder for simulated Lunar and Martian regolith to produce so-called ‘extraterrestrial regolith biocomposites (ERBs).’ In essence, HSA produced by astronauts in vivo could be extracted on a semi-continuous basis and combined with Lunar or Martian regolith to ‘get stone from blood’, to rephrase the proverb. Employing a simple fabrication strategy, HSA-based ERBs were produced and displayed compressive strengths as high as 25.0 MPa. For comparison, standard concrete typically has a compressive strength ranging between 20 and 32 MPa. The incorporation of urea — which could be extracted from the urine, sweat, or tears of astronauts — could further increase the compressive strength by over 300% in some instances, with the best-performing formulation having an average compressive strength of 39.7 MPa. Furthermore, we demonstrate that HSA-ERBs have the potential to be 3D-printed, opening up an interesting potential avenue for extraterrestrial construction using human-derived feedstocks. The mechanism of adhesion was investigated and attributed to the dehydration-induced reorganization of the protein secondary structure into a densely hydrogen-bonded, supramolecular β-sheet network — analogous to the cohesion mechanism of spider silk. For comparison, synthetic spider silk and bovine serum albumin (BSA) were also investigated as regolith binders — which could also feasibly be produced on a Martian colony with future advancements in biomanufacturing technology.

Preparation and evaluation of geopolymer based on BH-2 lunar regolith simulant under lunar surface temperature and vacuum condition

The construction of a lunar base and habitation on the moon has always been of great significance to utilizing lunar resources and deep space exploration. In this paper, a new type of lunar regolith simulant denoted as BH-2 of similar compositions and particle size distribution with real one was developed and used for geopolymer synthesis under simulated lunar surface temperature and vacuum conditions. The geopolymer products were characterized by compressive strength test, Mercury Intrusion Porosimetry (MIP), Scanning Electron Microscope coupled, and 29Si magic angle spinning-nuclear magnetic resonance (29Si MAS-NMR). The results showed that BH-2 lunar regolith simulant could be used to synthesize geopolymer. And the 72-h compressive strength of the geopolymer cured at the temperature of group C, corresponding to the 324–384 h of one lunar day, could reach 38.2 MPa, which was advantageous in the early stages of lunar construction because no additional curing equipment is required. The pores originated from lunar regolith simulant and caused by incomplete geopolymerization resulted in decreased compressive strength of the resulting geopolymer. Vacuum conditions on the moon favored the preparation of lunar geopolymers due to the lack of carbon dioxide weakening the efflorescence effect. This study benefits to lunar base construction with in-situ resource.

Rheological Properties of Lunar Mortars

NASA has revealed that they plan to resume manned missions and ensure the permanent presence of people in the so-called habitats on the Moon by 2024. Moon habitats are expected to be built using local resources—it is planned to use lunar regolith as aggregate in lunar concrete. Lunar concrete design requires a new approach in terms of both the production technology and the operating conditions significantly different from the Earth. Considering that more and more often it is assumed that the water present on the Moon in the form of ice might be used to maintain the base, but also to construct the base structure, the authors decided to investigate slightly more traditional composites than the recently promoted sulfur and polymer composites thermally hardened and cured. Numerous compositions of cement “lunar micro-mortars” and “lunar mortars” were made and tested to study rheological properties, namely, the consistency, which largely depend on the morphology of the fine-grained filler, i.e., regolith. For obvious reasons, the lunar regolith simulant (LRS) was used in place of the original Moon regolith. The used LRS mapped the grain size distribution and morphology of the real lunar regolith. It was created for the purpose of studying the erosive effect of dusty regolith fractions on the moving parts of lunar landers and other mechanical equipment; therefore, it simulated well the behavior of regolith particles in relation to cement paste. The obtained results made it possible to develop preliminary compositions for “lunar mortars” (possible to apply in, e.g., 3D concrete printing) and to prepare, test, and evaluate mortar properties in comparison to traditional quartz mortars (under the conditions of the Earth laboratory).

Thermal properties of lunar regolith simulant melting specimen

In this paper, investigations of two types of lunar regolith simulants, called TUBS-M and TUBS-T, developed by the Institute of Space Systems (IRAS) at TU Braunschweig are presented. These investigations are focused on the thermal properties, namely the specific heat capacity and the thermal conductivity. Several specimen of TUBS-M and TUBS-T were sintered at different temperatures with same holding times in order to investigate the influence of the sintering temperature on the thermal properties.The specific heat capacity was calculated resulting in an almost constant trend of both sintered simulants independent of the sintering temperature.To determine the thermal conductivity of the sintered simulants, the cooling behavior of the specimens was measured after heating them under vacuum conditions with a laser. This cooling behavior was simulated by a numerical model that solves the thermal conduction equation for the three-dimensional sample geometry. Both simulants show an increase of the thermal conductivity with increasing sintering temperature. After reaching a maximum at high sintering temperatures, the thermal conductivity starts to decrease.

Microstructural, mechanical, and thermal properties of microwave-sintered KLS-1 lunar regolith simulant

KLS-1 Lunar regolith simulant was microwave sintered to explore its potential applicability in future lunar construction. The effects of sintering temperature on linear shrinkage, density, porosity, and microstructural, mechanical, and thermal properties were investigated. As the sintering temperature increased, linear shrinkage and density increased and porosity decreased. Structural evolution in the sintered samples was characterized by scanning electron microscopy and X-ray diffraction. Unconfined compressive strength testing showed that mechanical strength increased significantly with increasing sintering temperature, with 1120 °C giving the highest strength of 37.0 ± 4.8 MPa. The sintered samples exhibited a coefficient of thermal expansion of approximately 5 × 10−6 °C−1, which was well-maintained even after cyclic temperature stress between −100 and 200 °C. Therefore, this microwave processing appears promising for the fabrication of building material with sufficient mechanical strength and thermal durability for lunar construction.