Solar 3D printing of lunar regolith

The end-of-life of the International Space Station, not beyond 2030, opens the path to new potential international collaborations to perform research in space. One idea is to settle a research centre on the lunar surface. It would be the first Moon village. The construction of a Moon village could however not be feasible without the use of in-situ resources and advanced manufacturing technologies. Thereupon, this work developed the first solar 3Dprinter that solely works with lunar regolith and sunlight. First, the research work focused on the sintering of glass beads and understanding the role played by the green body packing on the sintered material. Results showed that, during a sintering process, when the densest sample is targeted, the original packing fraction is a parameter quickly overtaken by a maximisation of the particles surface area. Then, traditional sintering of lunar regolith simulants exhibited the impact of each lunar mineral on the sintered product. Sintering five different simulants revealed the prominent role of plagioclase, active mineral affecting the sintering temperature. Ilmenite mineral, however, did not perturb the sintering process. Regarding the sintering atmosphere, vacuum had apositive impact on the sintering process, lowering the sintering temperature and increasing the material strength. Secondly, after a complete characterisation of the existing lunar simulants and studying of their sintering, JSC-2A lunar simulant was chosen for carrying out the solar additive manufacturing experiments. The idea was to sinter lunar regolith simulant layer-by-layerat the focal point of concentrated sunlight. At the DLR-Cologne solar oven, fluctuation in the Earth atmosphere prevented any successful additive manufacturing of lunar regolith simulant with actual sunlight. The experimental set-up was therefore adapted to the Xenon High-Flux Solar Simulator. Thus, the solar sintering process could run for several hours with steady light conditions. Adjusting the parameters, with a power density of 1.2 MW.m-2 focused on 20 mm diameter spot, it was possible to obtain the first solar 3D printed brick after 5 hours of sintering, layer-by-layer. Finite elements method analysis of the heat transfer — inside loose and sintered regolith— highlighted the quick cooling of the surface happening between the sintering of two layers. Temperature in homogeneities, which were responsible for thermal stresses within the sintered material and the warping of the edges, were also confirmed by the computer model. Microscopic and tomography analysis of the sintered parts showed discontinuous layers which are non-homogeneously merged together, with open and closed pores up to 500 µm. The mechanical properties showed that the material has a similar strength to gypsum. Latest sintered parts that are smaller, appeared to have a higher strength due to the reduced cooling time between the layers. Sintering mechanisms, presented in different cases, detailed the necessity of obtaining a suitable melt fraction and a hot substrate for stimulating interlayer bonding. Finally, improving this new technology in the near future was provento be beneficial for saving significant costs and providing a reliable radiation shield to the astronauts stepping onto the Moon tomorrow.