Twelve human beings have set foot on the Moon since the first – Neil Armstrong – in 1969. Nonetheless, the last spacewalk on the Earth’s natural satellite was over fifty years ago: on December 14, 1972. However, the wait should soon be over: NASA’s Artemis program plans to launch new human expeditions to the Moon by 2025. And the US space agency intends to go even further, starting in 2026 by establishing a permanent autonomous lunar base which could serve as an intermediate station for missions to explore Mars.
Such an ambition will obviously need to overcome countless challenges, including the provision of water, food, energy and oxygen supplies. Once on site, teams will also need items such as building blocks, tools and mechanical parts. Given the astronomical cost of space missions, it is essential to keep the weight of equipment imported from Earth to a minimum. That is why space agencies prefer to use in situ resources by exploiting materials already present on the lunar surface. This approach can also help meet the astronauts’ repair needs.
Laser-based powder bed fusion
The research activities of a team from IMT Mines Albi, including Thierry Cutard, are investigating these opportunities. “The additive manufacturing process would seem to be a natural candidate for this type of lunar production,” he states. “More specifically, our study focuses on small-scale technical objects, such as tools or filters, manufactured initially via laser fusion.” This is a mature process, which is already widely used on Earth, particularly in industry. It consists in spreading a bed of powder – often polymer or metal – and exposing it locally to a laser beam, which totally or partially melts the particles and solidifies the targeted part. This operation is then repeated, layer after layer, ultimately producing the 3D model initially designed on the computer. All that remains is to aspirate the unmelted powder in order to obtain the resulting object.
The research team’s ultimate aim is to adapt this process to lunar materials, for the manufacture of technical items that meet the criteria defined for geometry and mechanical strength. “Our work involves a certain amount of experimentation, but not exclusively,” says the researcher. “We also use numerical modeling and simulation for predictive and process optimization purposes.”
A rock similar to lunar regolith found in the Massif Central
On a practical level, what materials can the Moon provide? Primarily, lunar “regolith” – the name given to the dust covering the satellite’s surface. However, researchers from IMT Mines Albi cannot use this material directly because only a handful of samples have been brought back by space missions, in limited quantities. The research team’s first task was therefore to identify an analog material reproducing the chemical and mineralogical properties of lunar dust.
Lunar regolith is a member of the oxide family, combining atoms of metallic elements and oxygen in complex form. This is a welcome feature, since it shares similarities with many of the rocks found on Earth. “As lunar soil originates mainly from volcanic flows, the best terrestrial candidates can be found around volcanoes,” adds Thierry Cutard. “We therefore turned our attention to an analog material from a basaltic flow at the Pic d’Ysson in the Massif Central, identified by researchers from the Institut de recherche en astrophysique et planétologie [IRAP – French Astrophysics and Planetology Research Institute].”
Letting the powder tell its story
The sampled rock must then be reduced to a powder, with particle sizes similar to those found on the Moon, before the chemical and mineralogical compositions are checked against those of reference samples. “However, it’s impossible to perfectly imitate lunar regolith, which is exposed to constant radiation,” concedes the researcher. “In any case, that’s not our objective. We’re only aiming to get close enough to it for the results to be transposable to lunar applications.”
The powder is then ready to be used in the additive manufacturing machine (commonly known as a 3D printer), but this still needs to be configured to operate using the analog material. In the case of laser fusion, this means determining the power delivered, the size of the beam, the speed of travel and the degree of overlap between two passes… “To determine these parameters, we need to know how the powder will react to the radiation,” explains Thierry Cutard, “because its response may depend on the temperature, laser wavelength or both. Our work therefore enables us to precisely determine the thermal, thermo-optical and thermo-mechanical behavior of our analog material.” This information is essential for modeling radiation-matter interactions and optimizing machine settings.
Strengthening materials and reducing energy consumption
However, this manufacturing process is associated with a major difficulty: the products formed may be fragile. “These materials run the risk of cracking, especially due to the heat generated locally by the laser,” notes the researcher. “Manufacturing a crack-free item is therefore a real challenge.” To meet this challenge, in addition to optimizing the machine’s parameters, the research team is studying the possibility of mixing the analog material with another element, such as metal, to make the material stronger and stiffer.
Scientists are also considering the use of indirect additive manufacturing, i.e., combining the powder with an organic binder to bind the particles together temporarily. This method limits the risk of cracking, but requires additional treatment in an oven to sinter the material, thus increasing the duration and energy consumption of the operation.
However, researchers are not focusing solely on laser fusion. On the contrary, they are examining the possibility of using other less energy-intensive sources of radiation. “On a lunar station, energy supplies might be quite limited,” says Thierry Cutard. The IMT Mines Albi team has carried out promising initial tests using concentrated radiation from halogen lamps, and has started modeling the interactions between the powder and this new type of source.
From the Moon to the Earth
The results already obtained and those to come are regularly shared with other members of the scientific community, notably members of the “Toulouse Task Force” from IRAP, the Laboratoire de génie chimique (LGC – Chemical Engineering Laboratory) and the Institut Clément Ader. The research team has already successfully manufactured the first centimeter-sized objects resulting from laser fusion using the Pic d’Ysson analog, with satisfactory mechanical properties (hardness, compressive strength, etc.).
The next step is for the researchers to scale up their experiments by manufacturing products measuring around ten centimeters, while characterizing their performance. The form and function of these objects have yet to be defined, in consultation with partners such as the European Space Agency (ESA), the Centre National d’Etudes Spatiales (CNES – the French space agency) and space industry manufacturers. At the same time, the team is continuing to refine its multiphysical calculations and simulations, in order to provide models that faithfully represent reality.
What’s more, the study of additive manufacturing on the Moon could also be beneficial… on Earth. “Without this context of new space exploration-related plans, we may never have studied natural rock-based manufacturing processes,” says Thierry Cutard. “So why not apply these methods to terrestrial materials, from a sustainable development perspective?” Indeed, optimizing the sustainable exploitation of local resources, adapting to a constrained environment and limiting energy consumption are all highly topical and eminently down-to-earth issues today.
