“Why is cleaning spacesuits on the moon important?”

Lunar dust is an extremely abrasive material that can critically damage and compromise electronics, clothing, and life support systems. In addition, Astronaut Harrison Schmitt and others experienced an ailment they described as “lunar hay fever” from inhalation of lunar dust. Previous removal techniques using brushes, vacuums, and other fluid washes proved ineffective. These methods provided insufficient dust removal and often could damage systems. However, we may have found a solution using the dusting effect of cryogenic liquids.

“How did you notice the dusting effect of cryogenic liquids?”

Sometimes in our lab we “dust the floor” with leftover liquid nitrogen. The floor is far hotter than the boiling point of liquid nitrogen (which is about -196C or -321F), so the droplets skitter across the room, floating on their own boiling vapor. This is a result of the Leidenfrost Effect. Due to this effect the droplets pick up and collect dust from the floor as they move across it, finally depositing that dust when the droplet boils away completely. Could this effect be used to clean surfaces in extreme environments such as in lunar habitats?

Figure 1: Marked examples of liquid nitrogen lifting ash during boiling and Leidenfrost droplet formation

“How have you investigated the Leidenfrost effect?”

We knew that the Leidenfrost Effect cleaned dust from our floor but we didn’t know whether this would work with moon dust on astronaut suits. This is a new phenomenon, still open for research. While moon dust is nearly impossible to obtain, there are many substitutes that are close enough for initial testing. For our dust substitute we used ash that Washington State University has preserved from the Mt. St. Helens explosion. This ash was found to have a similar composition and particle shape to moon dust samples retrieved on the Apollo missions. Armed with this simulated moon dust, we began testing.

Figure 2: Scanning Electron Microscopy of Mt. St. Helens Ash (a,c,e) taken at Washington State University (10/2020) compared with Scanning Electron Microscopy of lunar regolith (Liu) (b, d, f, g). The images of Mt. St. Helens ash are on the left of the image. Images a and b picture glassy shards, images c and d picture glassy particles with coatings of fused particles (microlites/aggregated particles), and images e, f, and g show glassy/smooth particles).
Figure 3: Ash application to prepare Ortho-Fabric simulant for TRL 3 testing

Through basic testing, we found that a cryogenic wash is nearly twice as effective as water in removing Mt. St. Helen’s ash from a spacesuit simulant. Our proposed solution also requires no auxiliary power to function and is suitable for use in the airlock immediately upon return from extravehicular activity.

Figure 4: Ortho-Fabric simulant after ash and wash treatment with LN2 (bottom) or H2O (top)

“What is your plan?”

We are continuing testing employing a vacuum chamber. This will help mimic the environment of the lunar surface. We are also developing Computational Fluid Dynamics (CFD) models to model Leidenfrost droplet formation, dust collection, and behavior. After initial vacuum testing, we will design, build, and test a scaled shower system in an open and vacuum environment. This system will be a model of the final product harnessing the Leidenfrost Effect to clean spacesuits.

Thanks for listening!