## 1 Introduction  
The hostile space environment poses several technological problems for long-term human exploration. Thermal cycling and ionising radiation are two extreme challenges on the Moon, which, when considered together, make up one complex puzzle for engineers and architects of habitat construction to solve. Radiation exposure causes short- and long-term effects on the health of astronauts, e.g., cataract formation and carcinogenesis, respectively, and a prolonged exposure may pose serious threats to life [1, 2, 3]. Temperature extremes of \(-170\)\({}^{\circ}\)C and \(113\)\({}^{\circ}\)C [4] between the night and the day impose thermal stresses on materials and thermal cycling on the Moon can lead to thermal fatigue, potentially originating crack formation and propagation, thus presenting a threat to surface constructions. This study balances out the benefits of regolith utilisation as the main material for protection against galactic cosmic rays (GCR) and solar particle events (SPE) on the one hand, and for an adequate thermal environment inside the habitat on the other. Such an approach aims to outline the potential merit of regolith utilisation in habitats from a double point of view, ultimately allowing the definition of specifications for the architects designing the construction of future habitats on the Moon. Studies continuously evaluate the use of loose regolith, either through piling it up on top of an inflatable habitat, 3D printing, sintering or melting [5, 6, 7, 8]. The baseline of such designs relies on multilayer structures, using complimentary materials, such as polyethylene bags and aluminium foils, to contribute to the wall's stress resistance and thermal protection. Polyethylene and aluminium are used as standard materials in space exploration [9; 10]. In this paper, properties to further enhance radiation protection such as regolith compaction and multilayer materials are evaluated. The work presented here outlines different options for regolith compaction and utilisation which scopes out the architectural liberty in habitat construction. The available compression techniques and the amount of compaction that will be possible to make in situ will largely define the shape of future lunar habitats. The added value of this paper is in the proposal of a reasonably achievable protective layer from radiation which also satisfies the thermal insulation of the habitat. Regolith in a multilayer structure with aluminium and polyethylene, with regolith as the majority of the wall's thickness is evaluated for radiation protection of a lunar habitat; and thermal insulation properties are modelled during the 28 Earth days lunar cycles in order to anticipate what the temperature stability inside the habitat will be like. This study calculates the blood forming organs (BFO) dose and the effective dose equivalent in the computerised anatomical female (CAF) [11; 12]. SPE-induced BFO doses are considered to investigate the doses for short-term non-cancer effects. SPEs are short-term events which may present considerable harm to astronaut health. The authors anticipated that the SPE-induced doses would impose a larger constraint on regolith thickness than the GCR-induced doses. The latter ones result from an omnipresent continuous source of radiation, and the effective dose equivalent is thus calculated. As NASA's Artemis program [13] and following international Moon exploration will have mixed crews, and it is recognised that more sex-disaggregated data are required to draws conclusions on gender-specific radiation sensitivity [14] it is appropriate to base radiation protection for exploration type missions on the female model. The results are translated into quantitative recommendations on the minimum thicknesses and densities that the regolith layers should have in habitats for a generic long-term mission scenario on the Moon.