Water resources on the Moon are a critical component of international strategies for exploration of the solar system and space-based economic development. Liquid water is essential for human life support and propellant generation. Extreme Lunar conditions of near-vacuum and low temperature preclude the natural presence of liquid water; and they provide the thermodynamic context for water occurrence and its potential extraction. Ice crystals were observed by LCROSS and are inferred to reside in pore spaces of lunar regolith or at the surface in places. Any system proposed for lunar ice mining by induced sublimation needs to address potential vapor loss to the ambient near-vacuum; regolith cohesiveness; low regolith thermal conductivity; negligible sublimation rates below-200K; low rates of vapor advection-diffusion through porous regolith; and pressurization due to sublimation that causes redeposition. All of these obstacles have potential solutions with available technologies, but they must be designed within power availability constraints and with the potential to scale up to the resource needs of a growing space economy.

This work focuses on thermal water extraction on the lunar surface. We previously developed a three-dimensional finite element model (FEM) implementing heat and gas diffusion in the porous granular medium that is icy lunar regolith. Here, we present an improved version of this work in which we implemented a more realistic regolith model. In particular, we addressed previous model simplifications on regolith emissivity and porosity, water sublimation rate, as well as regolith and water ice thermal conductivity and permeability. Incorporating recent modeling and experimental work from the literature, we investigated the effect of these soil properties on the outcome of our simulations, with a particular interest in the yield of the thermal extraction process. Aiming at understanding what thermal water extraction would produce if heating the lunar surface directly, we also studied the effect of open borders on extraction yields. We find that the crude icy regolith approximation we implemented in Paper I provided a lower estimation of water vapor yields upon heating. Overall and using the same heating methods (surface heating as well as inserted drills), our more accurate regolith model implementation extracted more water from the simulation volume. With this new model, we observed that extraction yields depended mostly on the ice content of the regolith, and to a lesser extent on the heating configuration (number of drills) and power. In two specific configurations, 16 and 25 drills at 104 W in 1%vol icy regolith, heating allowed the extraction of nearby ice, efficiently desiccating the entire simulation volume. Apart from these two cases, the highest extraction yields were obtained for 104 W surface heating of a volume with closed borders with values over 80%. In open border volumes, highest yields were around 70% achieved for the highest number of drills (16 and 25), at the highest power (104 W) in the regolith with the largest icy fraction. Extraction masses started being noticeable around a few minutes, but reaching most of the maximum possible yields took up to several days in some cases. Defining an extraction efficiency by combining the yield and extraction times, we found that the best compromise between hardware complexity, time, and yield would be working in open border environments, using dense drill configurations in ice-rich regolith, and loose drill configurations in ice-poor regolith. In both cases, extraction efficiencies were similar at 102 W and 103 W per drill, indicating that low power solutions would yield similar results than higher power ones. Overall, our results support the viability of thermal water extraction in future ISRU architectures.

Recent discoveries of potential ice particles and ice-cemented regolith on extraterrestrial bodies like the Moon and Mars have opened new opportunities for developing technologies to extract water, facilitating future space missions and activities on these extraterrestrial body surfaces. This study explores the potential for water extraction from regolith through an experiment designed to test water recuperation from regolith simulant under varying gravitational conditions. The resultant water vapor extracted from the regolith is re-condensed on a substrate surface and collected in liquid form. Three types of substrates, hydrophobic, hydrophilic, and grooved, are explored. The system's functionality was assessed during a parabolic flight campaign simulating three distinct gravity levels: microgravity, lunar gravity, and Martian gravity. Our findings reveal that the hydrophobic surface demonstrates the highest efficiency due to drop-wise condensation, and lower gravity levels result in increased water condensation on the substrates. The experiments aimed to understand the performance of specific substrates under lunar, Martian, and microgravity conditions, providing an approach for in-situ water recovery, which is crucial for establishing economically sustainable water supplies for future missions. To enhance clarity and readability, in this paper, H2O will be referred to as water.

With the implementation of the Chang'E-5 mission in 2020,the three phases of China lunar exploration program,namely orbiting,landing and returning,have been completed.Next,the International Lunar Research Station (ILRS)will be established at the lunar south pole by 2030,and a lunar base will be planned later.It is a new era of exploitation and utilization of the Moon,in which a vast tasks should be completed.In this paper,we summarized some important progresses of investigation of lunar resources in the past,including lunar resource exploration,analysis of lunar volatiles,mineral extraction,and material construction by 3D printing of lunar regolith.Then,we proposed future tasks for the exploitation of the lunar resources.The main challenges of the Moon,such as the extreme lunar environment,unique properties of lunar regolith,and autonomous control of the process,were considered.The views in this paper can be referenced for future scientific researches and engineering tasks in the field.

Identifying the best technique for extracting water ice deposits in permanently shadowed regions at the lunar poles will be crucial in determining how successful a long-term or permanent settlement at these locations will be for future scientific and technology missions. This study uses a low-power microwave heating method to extract water from icy lunar simulants. Samples of lunar highland and mare simulants at different water contents (3-15 wt %) were heated using 250 W, 2.45 GHz microwaves. A maximum of 67 +/- 5% [2SD] of the water was extracted during heating runs of 25 min. Water was extracted more efficiently from the highland simulant than from the mare simulant. A significant reason for the different efficiency of water extraction in icy lunar simulants was the differing porosity of the samples made from different simulants. Pore space filled with ice leads to a reduced contact area between grains and an increased area of free ice, which causes poor heating performance. The results indicated that differences in chemical composition between the simulants had a negligible effect on water extraction, as the contact area between grains seems to dominate water extraction. This study found that low-power microwave heating is an effective technique for extracting water from cryogenic Icy simulants. It was also found that using a simple input energy principle (Input Energy = Absorbed Power x Heating Time) to es-timate the additional heating time was sufficient to overcome inefficient heating due to differing absorbed powers. For undersaturated samples, microwave heating was an efficient heating mechanism, but is less efficient for saturated samples where alternative heating methods may be more efficient at melting free ice before employing microwave heating.

We have used a three-dimensional thermal and gas diffusion model to study the heated extraction of water ice from lunar regolith. Both surface heating and the insertion of heated drills were investigated for various heating power levels and expected soil ice fractions. Our calculations rely on the use of the Crank-Nicolson finite difference method for the diffusion equations. We find that the extraction of water vapor from lunar regolith requires high levels of heating power in the investigated configurations. Any heating below about 1000 W per m 2 or per heated drill produces negligible amounts of vapor. We also find that extraction efficiencies are highly dependent on the heating configuration, as well as the initial ice fraction present in the regolith. In addition, we find that, depending on the heating configuration, significant amounts of water escape the heated volume and are lost through refreeze in colder regions. We conclude that water extraction through heating will be a power-hungry process if not optimized through additional controls (e.g. volume confinement by heated walls). In addition, the choice of a heating configuration for optimal extraction efficiency depends on the ice content of the soil. Therefore, detailed prospecting will be essential to the design of future ISRU activities on the Moon.