Establishing a permanent human presence on the lunar surface is a tough challenge considering the harsh in-situ environmental conditions. Aside high vacuum, abrupt temperature variations and radiations, micrometeoroids and small debris represent a major threat. In average, two meteoroids of one microgram hit each square meter of the lunar surface every year [1], at around 13 km.s-1 [2]. The significant amount of energy released during impact, as well as the random and unpredictable nature of such a risk, lead to consider the implementation of shielding over the critical installations. One of the key requirements applies to the material selection, for which as little Earth-based materials as possible shall be used. Regolith, the thin dusty layer covering the lunar surface, is the most abundant resource available, this is why its processing and potential applications are currently under research, especially for construction purposes [3]. One of the latest developments deals with the production of fibres out of lunar regolith simulant [4], which is the raw material selected for this work.

The design criteria for impact-resistant micro-meteoroid shielding may be complex to understand, hence inspiration was drawn from several natural structures, which have through evolution optimized their material consumption, selection and positioning, to achieve impact-resistant structures, essential for their survival under specific environmental conditions. Nacre, osteons and exoskeletons of insects and crustaceans are among the most tenacious structures already studied [5][6]. The understanding of the underlying energy dissipation mechanisms led to propose innovative bioinspired composite material architectures.

Given the level of complexity required by such structures, additive manufacturing was selected, more precisely the continuous filament fabrication technology. It enables the production of composite materials with a large design freedom and enhanced mechanical strength, compared to the traditional fused filament fabrication process, by taking advantage of the filament anisotropy [8]. The architecture manufacturing requires the generation of a specific printing path, given the continuous nature of the filament. Due to the limited amount of fibres made of lunar regolith simulant available, basalt fibres were chosen for lab-scale testing. The latter are pre-impregnated with an engineering thermoplastic material to produce the filament. The polymers encountered in the spacecrafts sent to the Moon and their payloads will eventually serve as a matrix for the composite filaments.

References
[1] M.I. Allende and al.; Prediction of micrometeoroid damage to lunar construction materials using numerical modelling of hypervelocity impact events International Journal of Impact Engineering, 2020
[2] H.A. Zook; The state of meteoritic material on the Moon Proceedings of the 6th Lunar Science Conference, 1975
[3] Cesaretti and al.; Building components for an outpost on the Lunar soil by means of a novel 3D printing technology Acta Astronautica, 2014
[4] Panajotovic and al.; MoonFibre – Fibres from Lunar Regolith RWTH Aachen, 2019
[5] Lazarus and al.; A review of impact resistant biological and bioinspired materials and structures Journal of Materials Research and Technology, 2020
[6] Ingrole and al.; Bioinspired energy absorbing material designs using additive manufacturing Journal of the Mechanical Behaviour of Biomedical Materials, 2021
[7] Gleadall: FullControl GCode Designer: Open-source software for unconstrained design in additive manufacturing 2021.
[8] Kabir and al.; A critical review on 3D printed continuous fibre-reinforced composites: history, mechanism, materials and properties 2020.