Upwards migration phenomenon on molten lunar regolith: New challenges and prospects for ISRU

As part of our research on the feasibility of producing commodities from lunar regolith by thermal-driven processes with minimal terrestrial precursors we need to characterize, reproduce, and understand thermophysical properties of the molten regolith still unforeseen under the lunar vacuum conditions at a scalable sample size. Two unanticipated phenomena, apparently caused by lunar melt’s surface tension under vacuum, have been revealed in our research work, vacuum void formation and upwards migration. In this paper we present our findings and thinkable explanation on the upwards migration phenomenon experimentally observed and consistently replicated as JSC-1A lunar regolith simulant melted at high vacuum. Upwards migration of molten lunar regolith will make future lunar ISRU’s melting processes both challenging as molten bulk material would migrate upwards along the container’s walls, and also promising on new opportunities for alternative ISRU’s sustainable processes as regolith’s upwards migration takes place in uniformed thin-film pattern. Among the potential ISRU’s processes that might use controlled thermal thin-film-based migration without the necessity of terrestrial precursors are production of feedstock for 3D printing, fractional separation of regolith’s component’s (O₂, metals, and alloys) via pyrolysis, film coating, purification of valuables solid crystals including silicon, and fabrication of key elements for microfluidic, and MEMS devices. Thermal upwards migration phenomenon on JSC-1A’s melt is formulated and explained by the authors as due to thermal Marangoni effect (also known as thermo-capillarity) in which temperature gradients within the melt’s bulk and along the crucible’s wall yield the surface tension large enough to supersede the gravitational force and yield the experimentally observed upwards thin-film migration. As far as the authors know, upwards thermal migration of molten JSC-1A (or other lunar simulant regolith) under vacuum has not been reported in the literature. A thermal mathematical model accounting for thermal Marangoni effect on molten JSC-1A agrees with what experimentally was observed, the formation of the meniscus on the melt-wall surface interface along with an incipient upwards migration in thin-film pattern along the crucible wall that, according to the model, experiences large temperature gradient, an important factor to trigger the thermal Marangoni effect along with the fact that surface tension of the molten lunar regolith material is temperature dependent.     

CAS-1 lunar soil simulant

Lunar soil simulant is a geochemical reproduction of lunar regolith, and is needed for lunar science and engineering researches. This paper describes a new lunar soil simulant, CAS-1, prepared by the Chinese Academy of Sciences, to support lunar orbiter, soft-landing mission and sample return missions of China’s Lunar Exploration Program, which is scheduled for 2004–2020. Such simulants should match the samples returned from the Moon, all collected from the lunar regolith rather than outcrops. The average mineral and chemical composition of lunar soil sample returned from the Apollo 14 mission, which landed on the Fra Mauro Formation, is chosen as the model for the CAS-1 simulant. Source material for this simulant was a low-Ti basaltic scoria dated at 1600 years from the late Quaternary volcanic area in the Changbai Mountains of northeast China. The main minerals of this rock are pyroxene, olivine, and minor plagioclase, and about 20–40% modal glass. The scoria was analyzed by XRF and found to be chemically similar to Apollo 14 lunar sample 14163. It was crushed in an impact mill with a resulting median particle size 85.9 μm, similar to Apollo soils. Bulk density, shear resistance, complex permittivity, and reflectance spectra were also similar to Apollo 14 soil. We conclude that CAS-1 is an ideal lunar soil simulant for science and engineering research of future lunar exploration program.     

Gas permeability and flow characterization of simulated lunar regolith

Recent discoveries of water ice trapped within lunar topsoil (regolith) have placed a new emphasis on the recovery and utilization of water for future space exploration. Upon heating the lunar ice to sublimation, the resulting water vapor could theoretically transmit through the lunar regolith, to be captured on the surface. As the permeability of lunar regolith is essential to this process, this paper seeks to experimentally determine the permeability and flow characteristics of various gas species through simulated lunar regolith (SLR). Two different types of SLR were compacted and placed into the permeability setup to measure the flow-rate of transmitted gas through the sample. Darcy’s permeability constant was calculated for each sample and gas combination, and flow characteristics were determined from the results. The results show that Darcy’s permeability constant varies with SLR compaction density, and identified no major difference in permeable flow between the several tested gas species. Between the two tested SLR types, JSC-1A was shown to be more permeable than NU-LHT under similar conditions. In addition, a transition zone was identified in the flow when the gas pressure differential across the sample was less than ∼40 kPa.     

月尘/月壤环境效应地面模拟方法研究

月壤/月尘会附着并污染航天器、月球车的表面,如果不及时清除,还会进一步诱发部件过热、机械机构卡死、密封失效、材料磨损等一系列问题.本文综述了关于月尘特性、月尘与航天器系统的互相作用机理、月尘环境模拟方法等方面的研究成果,提出了一种小型月尘环境模拟系统的设计方案.该系统将使关于月尘特性的实验研究成为可能,并可作为登月飞船及月球车材料选择、机械机构可靠性试验、除尘策略试验的平台.      

Moon surface radiation environment analysis for February 1956 solar event conditions

The radiation environment on the surface of the Moon presents a new source of particles resulting from the interaction of incoming solar protons and galactic cosmic rays with the lunar regolith. Here we present a study of the fluence profile of primary and secondary particles on the top 1 m layer of lunar regolith for the spectrum of one of the hardest spectrum solar event, that of February 1956. Different regolith compositions and their influence in proton and neutron production and backscattering is considered, as well as the nature of the backscattered radiation. Simple geometry Monte Carlo simulations have been used also for calculating regolith shielding properties, and it is shown that a layer of at least 50 cm regolith is needed for significantly reducing the dose levels received by astronauts in a hypothetical lunar habitat.     

Mechanical behavior of the metal parts welded with extraterrestrial regolith simulant by the solar concentrator in ISRU & ISRF application

The use of in-situ resources plays an important role on future extraterrestrial human activities for the facility repair and habitat construction, especially in sustainable space exploration of Moon and Mars. A method of the metal welded with extraterrestrial regolith simulant using solar processing under ambient conditions is presented. Metal parts are made of Q235B ferroalloy and TA2 titanium alloy into standard tensile members according to the ASTM code. They are disconnected from the middle in advance, and then welded together with lunar and Martian regolith simulant under ambient conditions, respectively. The entire welding process and precautions are detailed. Additionally, the mechanical behavior of weldments is characterized regarding their tensile strength. Furthermore, the fusion zone of weldments is studied by Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) measurements. The results show that it is possible to weld metal parts together with extraterrestrial regolith simulant by the solar concentrator. The average ultimate tensile strength of ferroalloy specimens welded with lunar and Martian regolith simulant is 2.94 MPa and 1.66 MPa; The average ultimate tensile strength of titanium alloy specimens welded with lunar and Martian regolith simulant is 4.95 MPa and 2.59 MPa. Moreover, the failure mode of all weldments was brittle failure. The welding joints strength derives from the phases that the regolith as the solder fusing into ferroalloys in a homogeneous way and titanium alloys in an inhomogeneous way. The presented method may provide a new thought for astronaut assistance associating with repairing and fabricating in subsequent Moon and Mars missions.     

Technical evaluation of additive manufacturing technologies for in-situ fabrication with lunar regolith

In-Situ Fabrication and Repair can significantly reduce the construction cost of a permanent Moon base by using additive manufacturing (AM) and exploiting local resources instead of bringing all the required materials from Earth. In this article, we evaluate alternative additive manufacturing technologies for building a lunar base and maintaining it across its lifecycle. We compare alternative 3D-printing techniques, already tested for manufacturing with simulants of lunar regolith, using energy, Earth-deliverables consumption, and compressive strength of the produced samples as figures of merit. Based on our analysis, we conclude that Cement Contour Crafting and Stereo-lithography AM techniques are the most promising solutions for the construction of outdoor lunar infrastructure and small precise parts and instruments, respectively.     

Development of thermal sensors and drilling systems for lunar and planetary regoliths

We consider some novel concepts for thermal properties experiments aboard lunar landers or rovers, that may lead to an improved understanding of both the structure of the lunar near surface layers and the lunar thermal history. The new instruments could be developed using the experience and heritage from recently developed systems, like the Rosetta Lander thermal conductivity experiment MUPUS and existing designs used for terrestrial measurements of thermal conductivity. We describe shortly the working principle of such sensors and the main challenges faced when using them in the airless regolith layers of the Moon or other airless bodies. In addition new concepts to create appropriate drill holes for thermal and other measurements in the lunar regolith are discussed.     

模拟月壤研制的初步设想

模拟月壤是月球样品的地球化学复制品，作者总结世界上已有的5种模拟月壤JSC-1，MLS．1，MLS-2，MKS-1和FJS-1的研制过程、方法与基本理化性质，认为系列化模拟月壤研制对中国首次月球探测有重要意义，在此基础上，作者提出系列化模拟月壤研制的基本思路．     

Study of complex dielectric properties of lunar simulants and comparison with Apollo samples at microwave frequencies

Laboratory characterization of dielectric properties of terrestrial analogues of lunar soil (JSC-1A) and comparison with lunar samples returned from various Apollo missions is made at different as well as normalized bulk density. Here measurements of dielectric constants and losses were made at four microwave frequencies such as 1.7 GHz, 2.5 GHz, 6.6 GHz and 31.6 GHz. Complex permittivity of lunar simulant was measured at temperature ranging from −190 °C to + 200 °C using Wave-Guide cell method. Comparison of permittivity of JSC-1A with Apollo sample also has been done at similar microwave frequencies. The investigations reveal that dielectric constant and loss factor of terrestrial analogues of lunar soil are temperature dependent. As temperature is gradually increased both these parameter (storage factor and loss factor) also gradually increases. These temperatures were chosen because the Moon undergoes at that extremes level of temperature. It is scorching heat at 110 °C during the day and freezing cold at −180 °C during night. The measured value of ε can be useful for designing passive as well as active sensors.     

Sulfur “concrete” for lunar applications – Sublimation concerns

Melting sulfur and mixing it with an aggregate to form “concrete” is commercially well established and constitutes a material that is particularly well-suited for use in corrosive environments. Discovery of the mineral troilite (FeS) on the moon poses the question of extracting the sulfur for use as a lunar construction material. This would be an attractive alternative to conventional concrete as it does not require water. However, the viability of sulfur concrete in a lunar environment, which is characterized by lack of an atmosphere and extreme temperatures, is not well understood. Here it is assumed that the lunar ore can be mined, refined, and the raw sulfur melded with appropriate lunar regolith to form, for example, bricks. This study evaluates pure sulfur and two sets of small sulfur concrete samples that have been prepared using JSC-1 lunar stimulant and SiO₂ powder as aggregate additions. Each set was subjected to extended periods in a vacuum environment to evaluate sublimation issues. Results from these experiments are presented and discussed within the context of the lunar environment.     

模拟月壤铺粉过程DEM数值仿真

空基激光选区熔化（SLM）技术与原位资源利用（ISRU）概念结合，有望解决地外大规模基地建设的工程难题。SLM铺粉过程对成形件性能和质量有重要影响。基于非球形粒子叠加球模型方法，建立模拟月壤颗粒几何模型；基于线性弹簧-阻尼接触作用模型、Hamaker理论及牛顿运动定律，建立颗粒动力学模型；采用三维离散单元方法（DEM）及软球模型，进行不同工况下模拟月壤在铺粉过程中的流变特性研究。结果显示:所提模型和方法能开展指定工况和环境参数的模拟月壤颗粒系统流动性和堆积行为数值仿真研究；月面低重力环境导致粉床表面粗糙度变大、堆积密度和平均配位数变小；通过降低铺粉速度和优化刮刀型面，可以有效改善月基铺粉的粉床质量，获得更密实和均匀的粉床结构。      

A drilling tool design and in situ identification of planetary regolith mechanical parameters

The physical and mechanical properties as well as the heat flux of regolith are critical evidence in the study of planetary origin and evolution. Moreover, the mechanical properties of planetary regolith have great value for guiding future human planetary activities. For planetary subsurface exploration, an inchworm boring robot (IBR) has been proposed to penetrate the regolith, and the mechanical properties of the regolith are expected to be simultaneously investigated during the penetration process using the drilling tool on the IBR. This paper provides a preliminary study of an in situ method for measuring planetary regolith mechanical parameters using a drilling tool on a test bed. A conical-screw drilling tool was designed, and its drilling load characteristics were experimentally analyzed. Based on the drilling tool-regolith interaction model, two identification methods for determining the planetary regolith bearing and shearing parameters are proposed. The bearing and shearing parameters of lunar regolith simulant were successfully determined according to the pressure-sinkage tests and shear tests conducted on the test bed. The effects of the operating parameters on the identification results were also analyzed. The results indicate a feasible scheme for future planetary subsurface exploration.     

三层月壤模型的多通道微波辐射模拟与月壤厚度的反演

由月球表面数字高程试验性地构造了整个月球表面月壤厚度的分布.根据Clementine探月卫星的紫外-可见光光学数据,计算了整个月球表面月壤中FeO+TiO2含量分布,给出了整个月球表面月壤介电常数分布.由月球表层温度的观测结果以及月壤的导热特性,给出了月尘层与月壤层温度随纬度分布的经验公式.在这些条件的基础上,建立了月尘、月壤、月岩三层微波热辐射模型.由起伏逸散定理,模拟计算了该月球模型多通道辐射亮度温度.然后,以此辐射亮度温度模拟加随机噪声为理论观测值,按三层模型提出了月壤层厚度反演方法.由于高频通道穿透深度小,由高频通道的辐射亮度温度按照两层月尘-月壤微波热辐射模型反演月尘层与月壤层的物理温度,再由穿透深度较大的低频通道辐射亮度温度反演月壤层厚度.对于反演的相对误差也进行了讨论.      

Effects of lunar and mars dust simulants on HaCaT keratinocytes and CHO-K1 fibroblasts

Exposure to lunar dust during Apollo missions resulted in occasional reports of ocular, respiratory and dermal irritations which showed that lunar dust has a risk potential for human health. This is caused by its high reactivity as well as its small size, leading to a wide distribution also inside habitats. Hence, detailed information regarding effects of extraterrestrial lunar dusts on human health is required to best support future missions to moon, mars or other destinations. In this study, we used several methods to assess the specific effects of extraterrestrial dusts onto mammalian skin by exposing HaCaT keratinocytes and CHO-K1 fibroblasts to dusts simulating lunar or mars soils. These particular cell types were chosen because the skin protects the human body from potentially harmful substances and because a well orchestrated program ensures proper wound healing. Keratinocytes and fibroblasts were exposed to the dusts for different durations of time and their effects on morphology and viability of the cells were determined. Cytotoxicity was measured using the MTT assay and by monitoring culture impedance, while phalloidin staining of the actin cytoskeleton was performed to address structural integrity of the cells which was also investigated by propidium iodide intake. It was found that the effects of the two types of dust simulants on the different features of both cell lines varied to a considerable extent. Moreover, proliferation of HaCaT keratinocytes, as analyzed by Ki67 labeling, was suppressed in sub-confluent cultures exposed to lunar dust simulant. Furthermore, experimental evidence is provided for a delay in regeneration of keratinocyte monolayers from scratch-wounding when exposed to lunar dust simulant. The obtained results will facilitate further investigations of dust exposure during wound healing and will ease risk assessment studies e.g., for lunar lander approaches. The investigations will help to determine safety measures to be taken during extraterrestrial expeditions in order to minimize risks to human health associated with exposure of human skin to dust contaminants.     

Investigating the soil removal characteristics of flexible tube coring method for lunar exploration

Compared with other technical solutions, sampling the planetary soil and returning it back to Earth may be the most direct method to seek the evidence of extraterrestrial life. To keep sample’s stratification for further analyzing, a novel sampling method called flexible tube coring has been adopted for China future lunar explorations. Given the uncertain physical properties of lunar regolith, proper drilling parameters should be adjusted immediately in piercing process. Otherwise, only a small amount of core could be sampled and overload drilling faults could occur correspondingly. Due to the fact that the removed soil is inevitably connected with the cored soil, soil removal characteristics may have a great influence on both drilling loads and coring results. To comprehend the soil removal characteristics, a non-contact measurement was proposed and verified to acquire the coring and removal results accurately. Herein, further more experiments in one homogenous lunar regolith simulant were conducted, revealing that there exists a sudden core failure during the sampling process and the final coring results are determined by the penetration per revolution index. Due to the core failure, both drilling loads and soil’s removal states are also affected thereby.     

月壤剖面冲击贯入式探测方案研究

以月壤剖面的原位探测为目标,提出一种利用土体结构侵彻原理的冲击式贯入器设计方案。重点阐述了冲击式贯入器的工作原理和机构实现方案,并开展多方案设计与分析。研制了原理样机并开展实验验证,证明利用冲击式贯入方法实现月壤剖面自动潜入的可行性,并对我国未来开展月壤剖面原位探测提出了相关建议。     

Phobos regolith simulants PGI-1 and PCA-1

The Martian moon Phobos is the target of the upcoming JAXA Martian Moons eXploration (MMX) mission. There are currently no known samples of Phobos, so spacecraft hardware testing and scientific studies require Phobos regolith simulants. Here, we present two new Phobos regolith simulants: Phobos Captured Asteroid-1 (PCA-1) and Phobos Giant Impact (PGI-1). These two simulants reflect the two hypotheses for Phobos’s formation, and thus the two broad possibilities for composition. This work follows previous efforts to document the development of mineralogically accurate simulants, in an effort to overcome past pitfalls with inappropriate uses of simulants. We report physical and geotechnical properties of PCA-1 and PGI-1, including their reflectance spectra, grain size distributions, abrasivity, cohesion, strength, and hardness. Our intent is for PCA-1 and PGI-1 to be open standards for Phobos simulants, and we present the simulant recipes and production methodology for use and modification by the community.     

Formation of polymer micro-agglomerations in ultralow-binder-content composite based on lunar soil simulant

We report results from an experiment on high-pressure compaction of lunar soil simulant (LSS) mixed with 2–5?wt% polymer binder. The LSS grains can be strongly held together, forming an inorganic-organic monolith (IOM) with the flexural strength around 30–40?MPa. The compaction pressure, the number of loadings, the binder content, and the compaction duration are important factors. The LSS-based IOM remains strong from ?200?°C to 130?°C, and is quite gas permeable.     

月球着陆器软着陆冲击仿真

为提高分析月球着陆器软着陆有效载荷着陆冲击响应的准确性,提出一种基于瞬态动力学的着陆器有效载荷软着陆冲击响应分析方法.根据着陆器全机结构柔性和月壤柔性对有效载荷着陆冲击响应的影响,参照某型着陆器,于MSC.PATRAN环境中建立着陆器全机柔性体模型及月壤柔性体模型,运用瞬态动力学仿真软件MSC.DYTRAN对着陆器软着陆有效载荷着陆冲击响应特性进行了仿真研究.仿真结果与试验结果具有一定的一致性.研究结果表明:使用该方法分析着陆器软着陆有效载荷的着陆冲击响应是准确有效的,能够比较逼真地模拟月球着陆器实际着陆工况.