Additive Manufacturing with Regolith on the Moon: Advancements of the ISRU Toulouse Taskforce

Additive manufacturing with regolith on the Moon: advancements of the ISRU Toulouse Taskforce J. Granier1,2 ([email protected]), T. Cutard1, P. Pinet2, Y. Le Maoult1, Thierry Sentenac1, S. Chevrel2. 1Institut Clément Ader (ICA); Université de Toulouse; CNRS, IMT Mines Albi, INSA, ISAE-SUPAERO, UPS; Campus Jarlard, F-81013 Albi, France, 2Institut de Recherche en Astrophysique et Planétologie (IRAP), CNRS/CNES, Observatoire Midi-Pyrénées, Université de Toulouse, France. Introduction: The progress of major space programs worldwide has shown for several years now that ISRU is key to the success of long-term human settlement on the Moon. The end of the decade is fast approaching, and with it the deadline for bringing to maturity the technologies that will ensure astronaut autonomy. The efforts made in additive manufacturing in particular, using regolith as a raw material, will be examined here. On a European scale, several innovative studies have already demonstrated the ability of technologies such as Selective Laser Melting (SLM) to produce parts, depending on numerous parameters, such as: - The object dimensions, allowing the manufacturing of large structures like paved roads [1] - The influence of the lunar environment, i.e., vacuum and low gravity [2] - The energy density used during the manufacturing step [3] However, the variations in experimental conditions between these different studies, both in terms of the nature of the starting material and the process parameters, make it difficult to compare the results obtained, thus preventing a global and quantitative analysis. The authors' objective is therefore to start from a previously identified and documented material, the lunar mare regolith analog BPY (Basalt of Pic d’Ysson) [4] and use it as a basis for both direct and indirect additive manufacturing. Its design principle, allowing modularity in chemical composition and maturity, is shown in Figure 1. In order to gain a better understanding of the phenomena involved in these processes, a campaign to characterize the various physical properties of BPY has been carried out and will be presented. Fig 1: Main steps of BPY analog preparation BPY physical characterisations: A total of three types of property have been analysed to date. Firstly, optical properties are used to estimate the type of radiation-matter interaction during direct additive manufacturing. The absorptivity of the different compositions of BPY analog has been estimated at room temperature, as well as during temperature rises to near-melting levels, using an experimental bench (BMEIR) for the measurement of infrared emissivity. Next, the ability of these materials to transfer heat has been addressed through the determination of thermal conductivity with the flash method, under several atmosphere natures, but also, once again, over a wide temperature range. For these optical and thermal aspects, analytical models from the literature are described and applied to BPY, and their possible limitations are specified. Figure 2 for example illustrates the Mellon thermal conductivity model [5] applied to crystalline BPY. Fig 2: Predicted thermal conductivity of BPY under air atmosphere mapped in function of temperature and pressure Finally, in the SLM process, the material undergoes significant physico-chemical transformations in a very short time. The overall analysis of these transformations in BPY during a first and then a second thermal cycle is carried out, using thermal analysis methods (DTA), dilatometry (TMA) and X-ray diffraction (XRD) to identify the crystalline phases. Everything considered, a significant amount of key data needed to build relevant numerical models for simulating additive manufacturing operations has already been acquired. Additive manufacturing trials: A recent study has focused on SLM trials on BPY using an SLM125HL system under an argon atmosphere [6]. The main parameters, defined by Volumetric Energy Density (VED), have been varied within a controlled range to explore defect formation and mechanical properties. Despite efforts to mitigate issues like cracking and porosity, challenges such as warping and local delamination persist. Three major aspects influencing the quality of the parts created are then identified: the nature and roughness of the substrate used, the proportion of amorphous phase present in the BPY (which drastically helps reduce porosity and so mechanical properties), and the effect of an annealing treatment when applied. For this last aspect, an in-depth study of annealed objects under TEM and CT scan helps to attribute the improved properties to the formation of a complex crystalline network composed mainly of diopsidic augite and forsterite, as presented in Figure 3. Fig 3: Thin section from a sample obtained by SLM, annealed then cut with FIB for TEM observations, SEM Conversely, indirect manufacturing using Fused Filament Fabrication, with the 3D Ceram M.A.T. machine, is now being introduced as an alternative, potentially reducing some of these challenges by preforming parts before sintering. Early-stage results suggest differences in porosity distribution and mechanical properties, which will be examined in future work. The discussion will address how these techniques can be combined strategically depending on mission constraints and component requirements. Conclusion and prospects: Significant progress has been made, showing interesting mechanical properties obtained on printed objects, up to 135MPa of compressive strength. The fabrication of complex structures, with good resolution, has been demonstrated as illustrated in Figure 4. These advances were made possible by a better understanding of the properties of the BPY analog and other simulants, and therefore indirectly of the lunar regolith. Major parameters such as particle size, temperature, pressure, amorphous matter content, and the application of annealing treatment are highlighted. The presentation will conclude with an opening on the need for European collaboration, to more effectively cover all the remaining parameters and thus accelerate the maturity of additive manufacturing technologies for ISRU. This could be done either by deciding on common printing conditions for a given technology or by selecting reference simulants and substrates. Defining a target object with the help of space agencies, with direct utility for astronauts, such as a heat exchanger, a particle filter, or even a porous pipe for irrigating crops, could make it possible to establish a set of targeted specifications. Finally, some technical limitations due to the type of material used could be circumvented. One of the main problems to be addressed is the brittle mechanical behaviour of the created objects and their high susceptibility to defects. Cermet structures using metallic powders produced with ISRU technologies, with the electrolysis of a variety of elements like aluminum, iron, magnesium, and titanium for example, could lead to improved ductility and toughness of the final product without degrading its hardness. Similarly, the application of the Bosch process to ISRU presented by Beau et al last year [7] demonstrated its ability to produce carbon powder that can be used for carboreduction purposes, enabling a cermet structure to be achieved in situ during the additive manufacturing phase itself. Fig 4: SLM-made gyroid structure, inscribed in a 2.5cm long cube References: [1] Ginés-Palomares J. et al. (2023) Sci Rep. 13, 15593. [2] Reitz, B. et al. (2021) Microgravity Sci. Technol. 33, 25 [3] Caprio L. et al. (2020) Additive Manufacturing 32 101029. [4] Granier J. et al. (2023), ELS 2023In-Situ Resource Utilization. [5] Mellon M.T. et al. (2022) Icarus 387 115211. [6] Granier J. et al, Acta Astronautica 226 (2025) 66–77. [7] Beau C. et al. (2024), ELS 2024 - In-Situ Resource Utilization.