Lunar Base Research Articles

Simulation of light environments inside lunar holes and their associated subsurface caverns

Vertical holes of several tens of meters in diameter and depth have been discovered on the Moon, potentially serving as skylights into subsurface volcanic caverns resembling lava tubes. Because of their scientific importance and potential for use as future lunar bases, these lunar holes and caverns are expected to be targets of intensive exploration in the near future. Using numerical simulations, this study investigates the light environment within a directly and/or indirectly sunlit subsurface cavern accessed through a skylight hole. We specifically analyze the Mare Tranquillitatis Hole (MTH), one of the largest lunar vertical holes, situated near the Moon's nearside meridian. The floor and walls of the hole, and the walls and ceiling of its associated subsurface cavern are lit by reflected sunlight from other parts of the hole and cavern, such as the floors, depending on the solar elevation angle. Furthermore, this paper presents estimation results for camera imaging for a case in which solar elevation angle is 45° in the morning, which is appropriate timing for exploration. Assuming reflectance of 0.1 for the lunar hole and cavern surfaces, we estimate the incident energy onto each pixel of a camera as it descends to the hole's floor. We specifically simulate conditions for a camera with a 12-bit dynamic range, similar to the wide-angle optical navigation camera (ONC-W) onboard the Hayabusa 2 spacecraft. The results suggest that a camera with a fixed gain would struggle to capture both directly and indirectly sunlit areas simultaneously, without saturating bright areas and ensuring minimum incident energy resolution (say, a 10 digital number) for darker areas. To overcome this challenge, adjusting the camera gain based on the hole's and cavern's illumination conditions is necessary.Graphical abstract

Silicate-lunar regolith composite: A vacuum self-hardened and comprehensively durable extraterrestrial construction material

Extraterrestrial exploration, represented by Lunar base construction, has been promoted worldwide as a multi-disciplinary, cutting-edge and strategic issue. Herein we proposed a novel extraterrestrial construction material composed of Lunar/Martian regolith simulants and only 4 wt% of silicate adhesive. This silicate-regolith composite can be directly self-hardened in vacuum within 4.5 h without any curing to achieve 29 MPa of hardening strength. Meanwhile, it shows comprehensive durability with stable microstructures and >70 % of residual strength against long-term vacuum exposure, huge temperature difference and intense γ-ray and proton radiations. Its in-situ solidification and durability originate from vacuum dehydration, where silica clusters in solution spontaneously cohere into a solid network with strong connections of silica tetrahedra and bound water. A moderate silicate modulus around 2.5 and appropriate modifications can disperse finer silica clusters to increase oligomer silica units in solution and enhance hardening strength. Compared with lunar geopolymer and other existing extraterrestrial construction materials, this vacuum self-hardening composite allows a cryogenic preparation even below −40 ℃ using diverse regolith with a wide range of compositions and sizes, proposing a facile, durable and versatile solution towards in-situ extraterrestrial constructions.

Lunar in-situ ironmaking through laser-assisted flash vacuum pyrolysis of iron oxide

The in-situ metallurgy of lunar regolith minerals for extracting metals and oxygen is a promising approach for the future construction of lunar bases. In this study, a novel laser-assisted flash vacuum pyrolysis (LFVP) method was proposed and developed for the production of metallic iron and oxygen from lunar regolith using iron oxide as raw material. First, the theoretical feasibility of vacuum pyrolysis of FeO was conducted through thermodynamic calculations. Subsequently, an experiment on laser heating of iron oxides was performed, with a reduction rate of FeO of approximately 15.5 % (±0.6 %). Scanning electron microscopy and transmission electron microscopy images revealed that the micronano-level metallic iron exhibited spherical particles, strip-like and irregularly shaped aggregates. The spatial distribution unevenness of the formed metallic Fe, differences in the condensation conditions of gaseous products, and the surface tension effects of liquid metallic iron were mainly attributed to the disparities in the morphology of metallic iron. Meanwhile, the process mechanism of vacuum pyrolysis of FeO was also analyzed. Therefore, LFVP of FeO for producing metallic iron represents a novel ironmaking technology, offering a promising solution for extracting metals and oxygen in situ from lunar minerals for future lunar base construction.

Partial gravity flammability of cast PMMA rods in concurrent axial stagnation flow

Testing was performed in a partial gravity centrifuge drop vehicle in the Zero Gravity Research Facility with cast PMMA rods in concurrent axial buoyant stagnation flow to determine flammability limits as a function of partial gravity level. The partial gravity levels studied varied from 0.04 g to a simulated 1g for ambient oxygen concentrations from 13.2 % to 15.2 % O2 by volume at an average 57.6 kPa (8.4 PSIA) ambient pressure, which is very close to the anticipated Lunar habitat pressure. The PMMA flammability boundary as a function of oxygen concentration and gravity level has been determined at five gravity levels. Coriolis effects appear to be minimal in the stagnation region where the flame is stabilized while the tips of the flame do show some bending at the higher gravity levels. Lunar gravity levels are near the minimum in the oxygen - gravity level flammability boundary. This suggests that fire is a significant safety risk for future exploration missions to the Moon since materials are screened in normal gravity to evaluate their safe use in space. If normal gravity screening is not conservative, a material derating method will need to be applied to ensure the material is not flammable on the Moon. Since the blowoff boundary appears to be linear with forced flow velocity, it may be possible to conduct elevated forced flow blowoff testing that could then be extrapolated down to effective Lunar gravity levels to provide an oxygen delta between 1g and Lunar flammability limits to derate the material.

A novel rigidizable inflatable lunar habitation system: design concept and material characterization

Constructing lunar bases is crucial as lunar missions progress towards utilization and exploitation. The challenging lunar environment, with its unique characteristics and limited resources, requires special materials, structures, and construction methods. Inflatable structures offer great potential for lunar construction due to their advantages in transportation, stowage, construction, and reliability. This paper proposes a rigidizable inflatable lunar habitat that maintains its shape even after air leakage, enhancing safety, durability, and fixability. The membrane material adapts to different requirements during transportation, construction, and service, achieved through solid-state actuation of shape memory polymer (SMP) for stiffness variation, allowing multiple moves and ground tests. This work comprises three parts: 1) system: design concept and construction processes, 2) material: design and characterization of restraint and rigidization materials, and 3) structure: numerical validation of structure properties. Finite element analysis, based on material models obtained through dynamic mechanical analysis (DMA) and tensile tests, demonstrates the effectiveness of including an SMP rigidization layer in preventing collapse and enhancing dynamic properties. This paper not only proposes a new system, but also provides material design methods and requirements, along with structural validation techniques. Findings validate the feasibility of rigidizable inflatable lunar habitats, applicable in extreme environments, also in temporary buildings, space structures, and soft robotics.

Flash sintering of HUST-1 lunar regolith simulant: Effects of processing temperature on microstructure characteristics and mechanical properties

In-situ construction method is expected to be considered for lunar base construction because of its reducing transportation cost. Among the many in-situ construction processes, the flash sintering process can significantly reduce the processing time and become a potentially effective in-situ resource utilization (ISRU) technology. In this study, the flash sintering process was investigated for the first time to realize the sample forming of HUST-1 lunar regolith simulant (LRS). The effects of sintering temperature on the micro- and macrostructural characteristics and mechanical properties of the samples were systematically studied. The results showed that the densities and mechanical properties of the sintered samples were improved with the increase of the sintering temperature (from 1050 °C to 1290 °C) in a low vacuum environment for 4 min. Joule heating effect was investigated to cause rapid high-temperature solid-phase reactions between the LRS particles. At 1290 °C, the compressive strength of the sintered sample reached maximum 59.47 MPa. This study provides an efficient forming method for lunar construction in the future.

Enabling High-Power Conditioning and High-Voltage Bus Integration Using Series-Connected DC Transformers in Spacecrafts

This article proposes a photovoltaic power processor for high-voltage and high-power distribution bus, between 300 V and 900 V, to be used in future space platforms like large space stations or lunar bases. Solar arrays with voltages higher than 100 V are not available for space application, being necessary to apply power conversion techniques. The idea behind this is to use series-connected zero-voltage and zero-current unregulated and isolated DC converters to achieve high bus voltage from the existing solar arrays. Bus regulation is then achieved through low-frequency hysteretic control. Topology description, semiconductor selection, design procedure, simulation and experimental validation, including tests in vacuum and partial pressures, are presented.

Simulating lunar highlands regolith profiles on Earth to inform infrastructure development and ISRU activities on the Moon

Lunar exploration and infrastructure development near the Moon's south pole, and at other future lunar settlements, demand a detailed understanding of the geotechnical properties, structure, composition, and stratigraphy of the near-surface lunar regolith. Long term exploration and development activities will require the use of regolith as a construction material for multiple structures, and as unrefined material for resource extraction during in situ resource utilization (ISRU) activities. Upcoming robotic and human exploration will be concentrated near the lunar south pole, which has a dominantly feldspathic composition typical of the lunar highlands. Past missions to lunar highlands terrain (Apollo 16, Luna 20) provide valuable “ground truth” data regarding the geomechanical properties of highlands regolith that serve as a guide for future exploration at the lunar south pole. Lunar highlands simulant LHS-1 has well-characterized geotechnical properties and is an appropriate analogue for highlands lunar regolith in terrestrial engineering studies. Cone penetrometer testing (CPT) measurements of LHS-1 reveal a strong exponential correlation between the G slope parameter and bulk density, which allows information to be obtained regarding the density profile of simulated regolith columns directly from CPT stress versus penetration curves. We show that LHS-1 can be used to replicate the near-surface regolith stratigraphy at the Apollo 16 highland landing region in Earth-based laboratories. The ultimate CPT penetration resistance measured in the laboratory under terrestrial gravity is not directly comparable to that measured under lunar gravity, and here we derive an average reduction factor of Rf = 0.29 to scale penetration resistance values to those measured in situ on the lunar surface. Geotechnical measurements of other lunar simulants combined with experiments similar to those described herein, tailored to the terrain type of interest, will provide crucial information to guide future regolith excavation, construction, and ISRU activities on the lunar surface.

Perturbation Detection in Space-based Human-Machine Teams (HMTs) in Different Layers

This study focuses on detecting unique and complex challenges of Human-Machine Teaming (HMT) in space missions, where coordination among humans, robots, and AI agents is critical. Such missions are beset by “perturbations”—unexpected challenges involving communication delays due to the vast distances separating team elements. These issues must be overcome to maintain the safety and effectiveness of space-based missions. This study conducted engineering tests to evaluate the impact of perturbations on communication and vehicle operations and the physiological state of the humans involved. It outlines an experimental scenario involving various space entities (e.g., lunar colonies; orbiters; rovers) to simulate space mission conditions and communication and coordination challenges. The study employs layered dynamics methods to detect perturbations in technological and cognitive team states across the mission, using sensors and information entropy as key analytical tools.

A Petri nets-based modeling method for multi robot path planning

The construction of lunar bases is one of the core enabling technologies in current lunar exploration and development plans of various countries. However, to eliminate the constraints of high transportation costs and limited manned space technology, a new research plan is to employ multi robot teams to build lunar bases. The key to this solution is how to achieve path planning for complex tasks for multiple robots. Therefore, this article takes the exploration and collection area, lunar soil collection, and lunar soil transportation in the lunar base construction scene as complex task inputs, and studies a multi robot path planning modeling method based on Petri net model. Firstly, a Petri net model for multi robot motion was constructed. Meanwhile, linear temporal logic(LTL) language was used to describe the related tasks of lunar base construction. Finally, simulation validation was conducted in Matlab software and compared with the modeling method using switching systems. The results show that the total modeling time required for using the Petri net model is reduced by two orders of magnitude compared to the modeling time for a single task switching system model, indicating that the established Petri net multi robot model has advantages such as avoiding dimension explosion and computational efficiency.

Solid waste management and resource recovery during the 4-crew 180-day CELSS integrated experiment

In order to explore the management and treatment methods of solid waste in the Controlled Ecological Life Support System (CELSS) of future lunar bases, during the 4-crew 180-day integrated experiment, the Solid Waste Management and Treatment System (SWMTS) was built, in which the treatment of recyclable solid waste such as inedible plant parts and human excrement was completed through a combination of biological aerobic composting and high-temperature oxidation. Basic data on the types and amounts of solid waste generated during the 4-crew 180-day experiment mission were obtained. There were six types of solid wastes, including the work support wastes, the household support wastes, the plant cultivation wastes, the plant-based wastes, and crew feces. The daily average production was 0.67, 1.4, 0.32, 8.48, 0.534 kg/d, respectively. The proportion of plant-based wastes was high as 74.3 %, indicating that it was the most important part. By closed-loop air drying and graded crushing, all 1526.97 kg of plant-based waste was treated, with water recovery (about 1163.87 kg), as well as volume reduction and stabilization treatment. By incineration and aerobic composting treatment, 67.3 % (244.4 kg) of the plant-based wastes (dry weight) and all of the feces (96.26 kg) were converted, providing 339.54 kg carbon dioxide for plant growth. And 90.6 kg organic fertilizer was obtained. The fertilizer was highly mature, met safety requirements, and effectively improved lettuce yield. The recycling rate of renewable solid waste during the experiment reached 89.8 %. The efficient circulation of solid waste had been achieved during the 4-crew 180-day integrated experiment. The long-time experimental results have shown that the established solid wastes management and treatment system can timely treat biomass solid waste such as inedible parts of plants and crew feces, achieve timely recovery of water in such solid waste, and recycle carbon and other elements, which effectively improved the material closure of the system and ensured the successful 4-crew 180-day experiment. This work also maybe lay the foundation for the construction and operation of an ecological life support system for future lunar bases.

Additive manufacturing development of construction materials for a lunar base via spark plasma sintering of volcanic rocks using in-situ resource utilization concept

This work presents an innovative approach for creating ceramic materials based on andesite-basalts for construction on the Moon. Employing the concept of in-situ resource utilization (ISRU), the authors simulated the composition of lunar regolith using volcanic rocks from Kamchatka and Primorsky Krai (Russia, Far East). These rocks were ground into submicron powders and sintered via spark plasma sintering (SPS) at temperatures of 800, 900, and 1000 °C. The resulting ceramic samples demonstrate exceptional physicomechanical properties comparable to lunar regolith – compressive strength up to 566 MPa and Vickers hardness up to 650 HV. Optimal characteristics were achieved at a sintering temperature of 1000 °C with a heating rate of 300 °C/min. It was determined that the heating rate during sintering has a decisive influence on the density of the resulting ceramics.This research vividly demonstrates the potential of SPS technology and the ISRU concept for creating high-strength construction materials on the Moon using local lunar raw materials, paving the way for large-scale construction of lunar bases utilizing the Moon's own mineral resources.

Conceptual design and experimental investigation of regolith bag structures for lunar in situ construction

Lunar habitat construction is a critical engineering requirement in lunar exploration missions, characterized by unique structural and material challenges distinct from Earth. To meet the demands of in situ large-scale construction in extreme lunar environments, a general mode of “Prefabricated core module & Inflatable structure &In situ materials structure” is adopted. This work analyzed the structural internal forces and foundation bearing capacity for lunar habitats, highlighting the significance of structural tensile performance and the foundation's allowable bearing capacity. A construction scheme based on regolith bags is proposed, encompassing architectural and structural design, and long-term planning. Multiscale experimental investigations conducted on “material, component, structure, and construction” levels confirm the excellent properties of regolith bag. Aramid fabric and CUG lunar regolith simulant were chosen for material and component testing, focusing on evaluating the regolith bag's performance under tension and compression. Successful construction demonstrations of a regolith bag arch structure and a regolith bag – airbag structural unit validate the feasibility of this construction scheme. Conclusively, the proposed lunar habitat construction scheme based on regolith bag technology provides a viable and efficient method for in situ lunar construction.

Control Effectiveness: Metric Development and Application to Resilient Lunar Habitat Design

System safety engineering in its bare essence involves identifying, assessing, and mitigating, or controlling, hazards. Appropriate safety controls are selected using hazard reduction precedence principles, prior experience, or by assessing their impact on residual risk (together with other factors like cost). We propose a control effectiveness metric as one way to systematically and consistently evaluate potential safety controls individually and thereby facilitate selecting a shortlist of potential controls for subsequent integrated evaluation. The control effectiveness metric considers a safety control’s availability when needed, the probability that its design is adequate in addressing the targeted hazard, the probability that the design will be implemented as intended, and the relationship between the time it takes for the safety control to address its target hazard and the time before the hazard propagates. We demonstrated the use of our metric on a lunar habitat design using a physics-based habitat simulator. High control effectiveness and safety controls result in a habitat with high resilience, while low control effectiveness results in lower resilience.

Cross-section extraction and model reconstruction of lava tube based on L1-medial skeleton

Lunar lava tube caves, due to their unique geographical structure and potential as shelters, have repeatedly emerged as prime candidates or priority areas during discussions on lunar base site selection. However, owing to current technological limitations and the complexities of lunar exploration, obtaining detailed data directly from the interiors of lunar lava tubes poses a significant challenge. Hence, the study of terrestrial lava tubes assumes critical importance. By delving into Earth’s lava tubes, we can gain insights into crucial aspects such as their formation mechanisms, geological characteristics, and stability, which can then inform and guide research on lava tubes found on extraterrestrial bodies like the Moon and Mars. During the data acquisition process for lava tubes, given their intricate spatial configurations and dim lighting conditions, we have opted to employ LiDAR technology to collect point cloud data, revealing the internal structural information of the lava tubes. Consequently, this paper thoroughly explores a method for extracting lava tube parameters and constructing models using this point cloud data. This approach encompasses four key steps: data preprocessing, axis construction of the lava tube, cross-sectional feature extraction, and 3D model reconstruction. Initially, raw data is refined through the creation of point cloud voxels to mitigate noise interference. Subsequently, an iterative algorithm is utilized to obtain the L1-medial skeleton, enabling precise capture of the lava tube’s axis information. Using this extracted axis, we proceed with sampling at fixed intervals to derive cross-sectional points of the lava tube. These points are then utilized to extract fundamental geometric parameters such as cross-sectional area, length, and width. Ultimately, by integrating all these cross-sectional point cloud data, a comprehensive 3D model of the lava tube is constructed. Remarkably, this method achieves a high degree of accuracy, with 99 % of the extracted cross-sectional points exhibiting an error of less than 0.12 m, and 99 % of the model’s positional errors falling within 0.15 m. This not only enhances the precision of parameter extraction but also provides significant technical support for in-depth studies of extraterrestrial volcanic activities and lava tube formation mechanisms. Furthermore, it offers a valuable tool for parameter extraction and research on other irregular natural tunnels.

The influence of lunar environment exposure on characteristics of nuclear energy He–Xe closed Brayton cycle

Compared with Earth, the lunar surface's environment is more complex, which suggests that the nuclear energy Helium–Xenon closed Brayton cycle (NHCBC), supplying electricity to the lunar base, may operate under off-design conditions. A thermodynamic model coupled with the lunar surface environment is established in this paper to analyze the effects of lunar environment exposure, including solar radiation exposure, lunar dust toxicity, and meteorite impact, on a given NHCBC. The results show that the output capacity of a given NHCBC is suppressed during the daytime and enhanced during the nighttime. The lunar dust will improve the system's output capacity at night but will also significantly inhibit the output capacity of the cycle during the daytime, resulting in a fluctuation of 824 % of the system without lunar dust. The output fluctuation of NHCBC is reduced after meteorite impact, while the output capacity of the NHCBC is suppressed, destroyed even worse. The optimization of cycle parameters can alleviate the influence of the lunar environment exposure on NHCBC to a minimal extent. This paper aims to analyze the impact of lunar surface environment exposure on the cycle parameters and output work characteristics of NHCBC and to provide some guidance for the subsequent application of nuclear energy in the lunar base.

Performance analysis of a bucket drum for lunar regolith collection in lunar base construction

To facilitate the collection of lunar regolith for lunar base construction, the use of a bucket drum has emerged as an efficient and convenient method. This paper aimed to investigate the influence of drum configurations and operating parameters on collection performance. Initially, a DEM model for lunar regolith simulant particles was developed, and parameters were calibrated using RSM. Three different drum configurations were designed for simulation to compare the motion behavior of particles, drum forces, torque, and collection mass. Additionally, the effects of the rotation speed, cut depth, and linear cut speed on collection process were analyzed through simulations. Furthermore, a testing platform was constructed to evaluate the collection performance of the drum under various operating parameters. The influence of operating parameters was further confirmed, thereby validating the effectiveness and accuracy of the DEM simulations. These findings offer valuable insights for optimizing drum structures and establishing appropriate operating parameters.

Assessing black soldier fly pupation and survival in lunar regolith simulant: Implications for sustainable controlled habitats on the Moon

Bioregenerative life-support systems (BLSSs) will be crucial for extended space missions and extraterrestrial habitats. The black soldier fly, Hermetia illucens, is recognized for its efficient organic waste consumption, making it well-suited for closed environments like spacecraft. Our study assessed H. illucens adaptability to different substrates, including a lunar regolith simulant, pertinent to future lunar colonization. Remarkably resilient, H. illucens prepupal larvae successfully pupated in all tested substrates, but pupation timing varied, with no-substrate larvae pupating later. Pupal stage duration also differed, particularly with lunar regolith simulant and sand treatments resulting in longer durations. Substrate treatments significantly influenced the number of emerged adults, with lunar regolith simulant yielding more adults than the no-substrate treatment. Additionally, sand and wood shavings treatments produced more adults, highlighting H. illucens adaptability to various substrates, including lunar regolith. These findings are crucial for future BLSSs design. Additionally, H. illucens adaptability to lunar regolith provides insights into life's adaptability in space environments, guiding future experiments on celestial bodies. This study provides critical data on how different substrates, including lunar regolith simulants, influence H. illucens development and survival, advancing BLSSs and ecological science in both space and terrestrial contexts.

PneumoPlanet: An Inflatable Moonbase Concept for the European Space Agency 1. Design and Location

One of the greatest objectives of space exploration today is to establish a permanent outpost on the Moon that would allow exploration of the lunar polar regions and the exploitation of local water resources. We envision this lunar outpost as a structure made up of inflatable elements, which would utilize solar energy to produce biomass, and thus, both oxygen and food for the astronauts. Due to the extremely low weight of the inflatable elements, we could build a very large infrastructure on the Moon with the help of only a few rocket launches. The low cost and the sustainable nature of such infrastructure can lay the foundation for a permanent human presence on the Moon. Keywords: Inflatable, Lunar Habitat, Moonbase, Illumination, Sustainability, Greenhouse, Cultivation

Iron-enhanced simulated lunar regolith sintered blocks: Preparation, sintering and mechanical properties

Lunar surface constructions face a hostile service environment, the objective of this study is to develop a lunar base construction material with excellent mechanical properties and superior durability. Based on the abundant iron (Fe) resources on the moon, simulated lunar regolith sintered blocks (CUG-1A) with varying Fe additions (0–10 wt%) were prepared by pressureless sintering, and their sintering characteristics, phase compositions and mechanical performance before and after high-low temperature treatment were studied. The results show that the introduction of the Fe phase noticeably improve the sintering quality and increase the relative density. Furthermore, the Fe phase significantly fortified the sintered blocks, when the Fe addition reached at 10 wt%, the blocks could achieve a compressive strength of 150.92 MPa and a tensile strength of 21.01 MPa. The Fe phase's reinforcement could stem from the mechanisms of promoting sintering, crack deflection and Fe phase bridging. Meanwhile, the high-low temperature treatment does not cause any substantial alterations in the blocks' mechanical strength nor their failure modes. Lastly, large-sized sintered blocks with high dimensional regularity were produced through process optimization, providing a reference for the construction of lunar bases.