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When the first astronauts walked on the moon as part of the , the concept of lunar habitats ceased being the stuff of science fiction and became a matter of scientific study. With several space agencies planning on sending crewed missions to the moon in the coming decade, these plans have become the subject of scientific interest again. Structures that will enable a "sustained program of lunar science and development" is the long-term aim of NASA's . China and the ESA have similar plans with the (ILRS) and the .

To limit the amount of materials that need to be launched for the moon and reduce reliance on Earth, these plans will incorporate local resources for building materials and resources— (ISRU).

In a published in Scientific Reports, researchers from Poland and the U.K. proposed a developmental pathway for a lunar habitat that begins with a dome built using a regolith-based geopolymer. This dome would enclose a 17-meter (~56 ft) diameter crater in the Mare Tranquillitatis region that would house all the necessary buildings for a lunar base.

The research was led by Magdalena Mrozek, a Research Assistant with the Faculty of Civil Engineering at the Silesian University of Technology in Gliwice, Poland. She was joined by Dawid Mrozek and Mateusz Smolana, also researchers from the Silesian University of Technology, and Lorna Anguilano, a Senior Research Fellow with the Brunel University London, and the Assistant Director of the Wolfson Center for Sustainable materials development and Processing.

The concept outlined in their paper represents a simplified concept for a lunar base that would leverage ISRU and the production of geopolymers on-site. The site location also offers several advantages, not the least of which is protection from meteoroid impacts and the ejecta these produce. They also selected a mare region, which are lower in elevation than highland terrains and have a higher crater density.

In addition, the Mare Tranquillitatis region near the (0.67 North by 23.47 East) was selected because of the sample data provided by . As Mrozek told Universe Today via email:

The authors analyzed the concept of a covering lid for their hypothetical lunar crater, which measures 17 meters (~56 ft) in diameter and 6 meters (~20 ft) in depth. This is consistent with craters in the Mare Tranquillitatis region, which average about 20 meters by 8 meters (65.5 by 26.25 ft). The next step was to conduct a numerical analysis to identify the appropriate dimensions and shapes for a lunar structure that could handle the load transfers and maintain an Earth-like atmospheric pressure (1,013.25 millibars or 1 bar) within. The next step was to select building materials that could handle the internal stress distributions and be produced on-site using local resources.

Ultimately, they selected lunar regolith-based geopolymers (GP), which consist of synthetic, inorganic monomers primarily composed of aluminum and silicon and have distinctive mechanical properties analogous to cement concrete. This is advantageous given that lunar regolith contains an average of 45% silicon oxide (SiO) by weight. The geopolymer they created consisted of a sodium hydroxide (NaOH) solution, sodium silicate water glass (NaO x nSiO x nHO), and the lunar highlands regolith simulant .

"The creation of building materials from original lunar regolith is not a viable option; therefore, one of the available lunar regolith simulants on the market must be used," said Mrozek. "We selected LHS, produced by Space Resource Technologies. Utilizing this material, we developed a geopolymer, which was subsequently tested to obtain the strength parameters that were input into the numerical model. The forces acting on a lunar structure differ significantly from those experienced on Earth; consequently, we needed to abandon certain methodologies applicable on Earth and re-examine the problem from a novel perspective.

The curing conditions for the samples were subjected to were selected to simulate lunar conditions in the Mare Tranquillitatis region. While temperatures range from 120°C during lunar day and -180°C during lunar night (248 to -292°F), they do not drop below 60°C (140°F) for seven terrestrial days, which is conducive to the geopolymerization process. With these considerations in mind, the team cured their samples in a thermal vacuum chamber at 60°C and a pressure of 50 hPa (50 millibars), consistent with the near-vacuum conditions on the moon.

After a total curing period of 28 days, the materials were subjected to bending and compression tests and analyzed using electron microscopy (SEM) and X-ray diffraction (XRD). These tests revealed that their regolith-based geopolymer had strength and elasticity comparable to masonry cement-sand calcium-silicate. The geopolymer and the design they selected could very well enable the construction of lunar bases in cratered mare regions, thus realizing a key goal of NASA's Artemis Program.

Said Mrozek: "We are civil engineers, which is why our paper concentrates on this specific area of inquiry. However, we are currently collaborating with a diverse range of specialists from various countries in disciplines such as architecture, physics, geology, and chemistry. We are currently engaged in preparations for the initiation of a project of a lunar base, which will be significantly more complex and detailed."