Moon dust can be painful – but it is also, quite literally, the ground we must traverse if we ever want a permanent human settlement on the moon. In this particular use case, its adhesive, jagged and static properties may actually be beneficial, according to a new paper recently published in Research by researchers at Beihang University who analyzed the mechanical properties of samples returned to the far side of the moon by the Chang’e-6 mission.
Chang’e 6 is the first mission ever to bring back samples from the far side of the moon. It collected some from the South Pole-Aitken (SPA) basin – the largest, deepest and oldest known impact crater in the solar system, which formed about 4.2 billion years ago. This formation caused significant changes in the geotechnical properties of its soil compared to those of the opposite side, previously collected by NASA astronauts and Chinese landers.
But it is difficult to test these properties on Earth. Simulants can’t really do justice to reality, and there simply aren’t enough real lunar regoliths on Earth to provide unlimited samples to every interested researcher. Performing some tests will also destroy the sample, making it useless for other research later. That’s why the authors came up with an alternative: perform non-destructive testing and then run a simulation.
Fraser explains how big a problem dust is.
They chose the discrete element method (DEM) for the model. This mathematical approach simulates the behavior of bulk solids by calculating the physical interactions, friction and collisions of millions of individual particles. As input, it takes the particle’s shape and some of its physical properties, and as output, it can create a “digital twin” of the soil that future rovers or astronauts will have to traverse without ever touching another sample.
To get there, however, the authors first had to touch some samples. To do this, they used high-resolution X-ray micro-computed tomography (micro-CT) to scale part of the sample returned by Chang’e 6. This non-destructive imaging technique, which also uses another technique called convolutional neural network, allowed the researcher to individually reconstruct nearly 350,000 individual particles for analysis.
Analysis of this data set showed some clear differences between the sample on the far side and those on the near side. Notably, the sample on the far side has fewer large, coarse particles than samples on the near side, but also that these particles have low “sphericity,” which measures how close a particle is to a true sphere.
Targeting dust with an electric field is one way to combat it, as Fraser explains.
After inserting this data set into their DEM program, the authors found that the regolith is exceptionally strong and is at the upper limit of measurements from Apollo-era samples. This is mainly due to a high internal friction angle and dust cohesion. Most likely, the jaggedness of the particles, which makes them so frustrating in machines or human lungs, is actually helpful in the context of improving their mechanical properties on the ground. Furthermore, the mechanical strength of the samples was increased by “cementation” by glassy agglutinates, most likely caused by a micrometeoroid impact. These make up about 30% of the sample and serve as a glue that holds the remaining particles together.
To build large-scale infrastructure such as a future Artemis habitat or the International Lunar Research Station, understanding the fundamentals of soil is crucial. This unique geotechnical investigation of the other side shows how diverse the samples can be. And while it may take a while to really build anything on the other side (due to communication issues), it’s still good to know that when we do, there’s a solid foundation waiting for us. Even if that same solid ground could eventually destroy our machines and kill us if exposed to it for too long.
Learn more:
Research / EurekaAlert – Building on the other side: AI analysis suggests more stable foundations for future moon bases
H. Wang et al. – Particle morphology controls bulk mechanical behavior of far-side lunar regolith from Chang’e-6 samples and deep learning
UT – The sticky moon dust problem gets a mathematical solution
UT – Flexible force fields can protect our return to the moon
