Quality of 3D printing with lunar regolith varies based on feedstock

Lately, there’s been plenty of progress in 3D printing objects from the lunar regolith. We’ve reported on several projects that have attempted to do so, with varying degrees of success. However, most of them require some additive, such as a polymer or salt water, as a binding agent. Recently, a paper from Julien Garnier and their co-authors at the University of Toulouse, published in Acta Astronautica, attempted to make compression-hardened 3D-printed objects using nothing but the regolith itself.

Getting things into space is expensive, so it should be no surprise that any 3D printing technology that requires shipping large amounts of things from Earth is at a disadvantage. Various projects, like one being run by a company called AI Spacefactory, utilize additives like polymers that must be made on Earth and then shipped to the moon before being combined with regolith in situ.

Dr. Garnier hoped to get around that requirement by using selective laser melting (SLM) on a specific type of regolith analog. Known as Basalt of Pic d’Ysson (BPY), this volcanic rock is collected from the Pic d’Ysson, an ancient, extinct volcano in France. It started growing in popularity as a lunar regolith simulant in the early 2000s due to its chemical and mineral composition similarity to basaltic rocks found on the moon itself.

BPY has already been the target of several studies in lunar 3D printing. ESA researchers have published a paper detailing a “solar sintering” technique that uses the sun’s power to fuse BPY powder. Project MOONRISE, which we’ve reported previously, also used BPY as a feedstock in its zero-gravity 3D printing applications.

However, most of those studies have found that the BPY wasn’t up to snuff when 3D printed, at least in terms of the compression strength of the resultant material. Despite the moon’s lower gravity, there are still stresses on the structures of buildings and equipment on the moon. If a material’s compressive strength can’t handle that weight, even in the lower gravity, then it’s not much use as a building material.

Measurements for the compressive strength of 3D printed BPY vary dramatically based on the type of 3D printing technique used. Powder Bed Fusion processes, which are regularly used to print metals on Earth, had a compressive strength of 4.2 MPa, slightly more than a standard masonry brick. However, that was with a porosity of almost 50%—meaning nearly half the structure was full of holes. Combining 3D printed BPY with a geopolymer binder can increase its strength, but at the cost of requiring the geopolymer to be shipped from Earth.

The researcher Dr. Garnier and his co-authors focused on trying to uncover what properties of the BPY could lead to better mechanical properties. They varied characteristics like whether the powder was primarily “crystalline” or “amorphous.” Crystalline powder has a very ordered structure, with some properties, such as compressive strength, varying widely depending on the direction the ordered crystal structure points. On the other hand, amorphous powder is much more disordered, with its physical properties being the same in all directions.

Experiments showed a doubling in the compressive strength of powder that was 100% crystalline compared to powder that was 100% amorphous, highlighting the importance of the regolith structure selected to build the building materials of any future lunar base.

Optimizing that mix between amorphous and crystalline structure remains on the list of things to do for future work, as well as optimizing the size of particles in the feedstock and the parameters used in the SLM process to create the final material. There’s still a long way to go before astronauts can print something usable on the surface of the moon. But as the date for humanity’s return draws closer, it’s probably only a matter of time before a mission does make use of the resources available on our lunar neighbor—and they might do so by melting it with a laser.