Lunar soil, as an in-situ resource, holds significant potential for constructing bases and habitats on the Moon. However, such constructions face challenges including limited mechanical strength and extreme temperature fluctuations ranging from -170 degrees C to +133 degrees C between lunar day and night. In this study, we developed a 3D-printed geopolymer derived from lunar regolith simulant with an optimized zig-zag structure, exhibiting exceptional mechanical performance and thermal stability. The designed structure achieved remarkable damage tolerance, with a compressive strength exceeding 12.6 MPa at similar to 80 vol% porosity and a fracture strain of 3.8 %. Finite element method (FEM) simulations revealed that the triangular frame and wavy interlayers enhanced both stiffness and toughness. Additionally, by incorporating strategically placed holes and extending the thermal diffusion path, we significantly improved the thermal insulation of the structure, achieving an ultralow thermal conductivity of 0.24 W/(m K). Furthermore, an iron-free geopolymer coating reduced overheating under sunlight by 51.5 degrees C, underscoring the material's potential for space applications.

In situ resource utilization of lunar regolith provides a cost-effective way to construct the lunar base. The melting and solidifying of lunar soil, especially under the vacuum environment on the Moon, are the fundamentals to achieve this. In this paper, lunar regolith simulant was melted and solidified at different temperatures under a vacuum, and the solidified samples' morphology, structure, and mechanical properties were studied. The results indicated that the density, compressive strength, and Vickers hardness of the solidified samples increased with increasing melting temperature. Notably, the sample solidified at 1400 degrees C showed excellent nanohardness and thermal conductivity originating from the denser atomic structure. It was also observed that the melt migrated upward along the container wall under the vacuum and formed a coating layer on the substrate caused by the Marangoni effect. The above results proved the feasibility of employing the solidified lunar regolith as a primary building material for lunar base construction.

The lunar base establishing is crucial for the long-term deep space exploration. Given the high costs associated with Earth-Moon transportation, in-situ resource utilization (ISRU) has become the most viable approach for lunar construction. This study investigates the sintering behavior of BH-1 lunar regolith simulant (LRS) in a vacuum environment across various temperatures. The sintered samples were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM), along with nanoindentation, uniaxial compression, and thermal property tests to evaluate the microstructural, mechanical, and thermal properties. The results show that the sintering temperature significantly affects both the microstructure and mechanical strength of the samples. At a sintering temperature of 1100 degrees C, the compressive strength reached a maximum of 90 MPa. The mineral composition of the sintered samples remains largely unchanged at different sintering temperatures, with the primary differences observed in the XRD peak intensities of the phases. The plagioclase melting first and filling the intergranular pores as a molten liquid phase. The BH-1 LRS exhibited a low coefficient of thermal expansion (CTE) within the temperature range of - 150 degrees C to 150 degrees C, indicating its potential for resisting fatigue damage caused by temperature fluctuations. These findings provide technical support for the in-situ consolidation of lunar regolith and the construction of lunar bases using local resources.

The exploration of the Moon necessitates sustainable habitat construction. Establishing a permanent base on the Moon requires solutions for challenges such as transportation costs and logistics, driving the emphasis on In-Situ Resource Utilization (ISRU) techniques including Additive Manufacturing. Given the limited availability of regolith on Earth, researchers utilize simulants in laboratory studies to advance technologies essential for future Moon missions. Despite advancements, a comprehensive understanding of the fundamental properties and processing parameters of sintered lunar regolith still needs to be studied, demonstrating the need for further research. Here, we investigated the fundamental properties of lunar regolith simulant material with respect to the stereolithography-based AM process needed for the engineering design of complex items for lunar applications. Material and mechanical characterization of milled and sintered LHS-1 lunar regolith was done. Test specimens, based on ASTM standards, were fabricated from a 70 wt% (48.4 vol %) LHS-1 regolith simulant suspension and sintered up to 1150 degrees C. The compressive, tensile, and flexural strengths were (510.7 +/- 133.8) MPa, (8.0 +/- 0.9) MPa, and (200.3 +/- 49.3) MPa respectively, surpassing values reported in previous studies. These improved mechanical properties are attributed to suspension's powder loading, layer thickness, exposure time, and sintering temperature. A set of regolith physical and mechanical fundamental material properties was built based on laboratory evaluation and prepared for utilization, with the manufacturing of complex-shaped objects demonstrating the technology's capability for engineering design problems.

In-Situ Resource Utilization (ISRU) approaches hold significant importance in plans for space colonization. This work explores a different ISRU concept applying fast-firing, a robust and well-known industrial process, to Mars regolith simulant (MGS-1). The fast-fired specimens were compared to the ones obtained by conventional sintered under low heating rates. When the holding time at the firing temperature is longer than 15 min, fast-fired specimens exhibited higher density and flexural strength (> 35 MPa) than conventional sintering. For both processes, the bulk density values and the mechanical properties of the regolith compacts were enhanced with increasing dwell time. This was attributed to higher heating rates changing the densification/crystallization kinetics involving the basalt glass in the regolith composition. Specifically, high heating rate promotes sintering over crystallization. On these bases, fast firing can be considered a potential candidate for ISRU on Mars.

The discrete element method (DEM) is one of the most popular methods for simulating lunar soil simulants due to the lack of real lunar soil. To reduce the computational consumption and difficulty because of complex particle models, simplified particle models, in which a single particle consists of two, four, or six elements, are discussed in this paper. Three steps, including random generation, particle replacement, and sedimentation, can generate the proposed simulant. The relationship between the mechanical properties of the simulant and microscopic parameters defined in DEM was analyzed by the orthogonal array testing (OATS) technique. Then, the prediction functions, which can calculate mechanical properties from inputting the microscopic parameters without carrying out the DEM, are also established by a back-propagation artificial neural network (BP-ANN). The widely used physical simulants JSC-1 from the USA and FJS-1 from Japan are simulated in DEM from the prediction function with high accuracy.

Preparing regolith-based composites for 3D printing is crucial in lunar base construction, leveraging costeffective and mechanically favorable materials for lunar construction by utilizing lunar regolith as the reinforcing phase. This research focuses on developing lunar regolith simulant as a matrix for 3D printing, which is crucial for in-situ resource utilization on the Moon. Resin-based composites, well-established in aerospace, are explored for their simple manufacturing and robust properties. The formulation involves simulated regolithbased polymer for direct ink writing printing. Rheological properties, including yield stress and plastic viscosity, are characterized across various cementite-sand ratios and printing temperatures. The relationship between extrudability, the time interval of the printing material and its rheological attributes is investigated. Quantitative assessment of material buildability employs three-dimensional scanning of the printed parts. Freeze-thaw cycle tests explore its temperature resilience. The influence of varying the printing infill rate on printing efficiency and the performance of the printed parts was assessed. It was found that modulating the printing infill rate affects the efficiency and performance of parts, with a 1:4 cementite-sand ratio and a 40 degrees C print temperature demonstrating optimal printing workability. These findings offer an efficient scheme for the automated production of regolithbased epoxy composites with precise structural, temperature-resistant, and favorable mechanical properties.

Grain size distribution (GSD) is crucial for understanding soil properties and surface processes. We find that both terrestrial soils and lunar soils are subjected to a unified GSD function, P(D)= g(mu )D-mu exp(-D/Dc), reducing the textural fractions and grade modes to a parameter pair (mu, Dc), which unifies terrestrial and extraterrestrial soils in granular configuration, beyond the environments and mechanisms of soil genesis. To construct a framework of the soil formation, we generalize the textural composition to a grade space representing the granular configuration, and conceptualize soil genesis as the random aggregation of the fractal fragmentation of parent lithospheric material and fragments from other sources (e.g., meteorites impacts or surface transport processes). Random simulation reproduces the multiple grade modes observed in soils, and spontaneously derives the unified GSD function. Then we numerically generate the (mu, Dc)-fields for soils on earth and moon, which refine the digital data mapping based on site measurements and depict the local fluctuation of soil parameters. The GSD unity also provides a tool of generating numerical simulants of lunar soils to fill the gap in material simulants. The study leads to a GSD-paradigm (in contrast to the conventional landscape-paradigm) in soil study, which is expected to facilitate the data harmonization on earth and promote the generation of lunar regolith data in favor of the in-situ resource utilization and base construction on moon.

Mars is increasingly considered for colonization by virtue of its Earth-like conditions and potential to harbor life. Responding to challenges of the Martian environment and the complexity of transporting resources from Earth, this study develops a novel geopolymer-based high-performance Martian concrete (HPMC) using Martian soil simulant. The optimal simulant addition, ranging from 30% to 70% of the total mass of the binders, was explored to optimize both the performance of HPMC and its cost-effectiveness. Additionally, the effects of temperature (-20 degrees C-40 degrees C) and atmospheric (ambient and carbonated) curing conditions, as well as steel fibre addition, were investigated on its long-term compressive and microstructural performance. Optimal results showed that HPMC with 50% regolith simulant achieved the best 7-day compressive strength (62.8 MPa) and the remarkable efficiency improvement, a result of ideal chemical ratios and effective geopolymerization reaction. Under various temperature conditions, sub-zero temperatures (-20 degrees C and 0 degrees C) diminished strength due to reduced aluminosilicate dissolution and gel formation. In contrast, specimens cured at 40 degrees C and 20 degrees C, respectively, showed superior early and long-term strengths, with the 40 degrees C potential for moisture loss related shrinkage cracking and reduced geopolymerization. Regarding the atmospheric environment, carbonation curing and steel fibre addition both improved the matrix compactness and compressive strength, with carbon-cured fibre-reinforced HPMC achieving 98.3 MPa after 60 days. However, long-term exposure to high levels of CO2 eventually reduced the fibres' toughening effect and caused visible damages on steel fibres.

Establishing a permanent, self-sufficient habitat for humans on planetary bodies is critical for successful space exploration. In-situ resource utilisation (ISRU) of locally available resources offers the possibility of an energy-efficient and cost-effective approach. This paper considers the high-temperature processing of molten lunar regolith under conditions which represent the lunar environment, namely low gravity, low temperature, and negligible atmospheric pressure. The rheological properties of the low-titanium lunar mare regolith simulant JSC-1A are measured using concentric cylinder rheometry and these results are used to explore the influence of viscosity on processing operations involving the flow of molten regolith for fabricating construction components on the Moon surface. These include the delivery of molten regolith within an extrusion-based 3D printing technique and the ingress of molten regolith into porous structures. The energy and power required to establish and maintain sufficiently high temperatures for the regolith to remain in the liquid state are also considered and discussed in the context of lunar construction.