「lunar hay fever (Lunar hay fever). Of course there is no pollen on the moon. The causative agent is regolith on the surface of the moon. Regolith, which is the sand that covers the moon’s surface, is extremely fine and sharp, unlike sand on Earth. When an astronaut is active on the moon, regolith adheres to the surface of his space suit and is brought into the spacecraft. Regolith, which is a particle so small that it cannot be seen, irritates the mucous membranes of the eyes, nose, mouth, lungs, etc., causing sneezing and itching just like hay fever. This is the true identity of lunar pollinosis.
By the way, as the term lunar pollinosis was coined by Apollo 17 crewman Harrison Schmidt, this problem has been pointed out since the Apollo program half a century ago. Harm from fine dust is a well-known health risk, including pneumoconiosis.Harm from regolith is not limited to temporary symptoms, but may affect the respiratory system in the long term and pose a carcinogenic riskThere is alsoIn addition, the main body of the spacecraft, the engine, the space suit, etc.If dust gets into the gaps of precision equipment, it may cause malfunction or damage.It will also be.
In fact, during the Apollo program, there was a case where a spacesuit was damaged to the point where it became unusable. An attempt was made to remove the regolith by brushing following the lunar activity, but it was not very effective in removing the regolith that had adhered to it due to static electricity. did not. In addition, brushing may damage the fabric of the space suit. For future manned lunar explorations such as the Artemis program, a longer stay on the moon than the Apollo program is planned, so “washing spacesuits” will be a realistic issue.
【▲ Figure 1: Liquid nitrogen poured into lunar regolith mimetic (Credit: Wells, et.al. / Washington State University)】
Research teams such as I. Wells at Washington State University and othersLiquid nitrogen spray is the best way to clean spacesuitsreported the result that When cold liquid nitrogen is sprayed onto the spacesuit, the liquid nitrogen evaporates as it heats up the warmer spacesuit, entraining the regolith. At this time, vaporized gaseous nitrogen creates a small gap between the atomized droplet of liquid nitrogen and the fabric of the space suit, temporarily blocking heat transfer, and the droplet disappears immediately. I don’t. This phenomenon isLeidenfrost phenomenon” is called. In this state, the droplets of liquid nitrogen naturally move over the fabric and coalesce with each other, facilitating the removal of the regolith.
Liquid nitrogen seems to be suitable for cleaning space suits because of its ease of handling, safety, resource availability, and other advantages in terms of cost. However, the effect of spraying liquid nitrogen under vacuum and the damage to the fabric caused by repeated spraying were unknown until now. Therefore, Mr. Wells and his colleagues attach substances used as substitutes for lunar regolith, such as earth’s volcanic ash and sand, artificial lunar soil, to a black miniature space suit that is regarding one-sixth the size of the real thing. We conducted an experiment to spray liquid nitrogen.
[▲ Figure 2: The 1/6 scale miniature spacesuit used in the experiment. From left: images with simulated regolith attached, following liquid nitrogen spraying with a fixed nozzle, and following liquid nitrogen spraying with a fixed nozzle and a handheld sprayer. A spray of liquid nitrogen removes the whitish pseudo-regolith, revealing a black fabric color (Credit: Wells, et.al./Washington State University)]
As a result, it was found that liquid nitrogen exhibited better regolith removal performance in a vacuum than in the presence of air. Experiments in which the miniature spacesuit was sprayed with liquid nitrogen from different angles achieved an average mass removal rate of 98.4%. this is,10µm in diameter (0.01mm) Can remove 95.9% of regolith belowequivalent to
Furthermore, in a re-removal test in which dust was adhered once more following washing twice and sprayed with liquid nitrogen, a 2.66% improvement in removal rate was confirmed. This is probably caused by dust that has not been removed in previous washes and has become lodged in the fibers of the fabric. It is presumed that the clogging of the fabric prevented other dust from entering the fibers, and as a result, the dust became easier to remove. Also, as a result of performing a total of 233 removals,Fabric damage occurs on average 75 timesI also understand.In the Apollo program, the fabric was damaged following just one brushing removal.Considering that, this is a very good result.
This research, which was conducted with a grant from NASA, won the first prize in 2021 at NASA’s student contest “BIG Idea Challenge (Breakthrough, Innovative and Game-changing Idea Challenge)”. However, since this experiment is currently being conducted in an ordinary laboratory, it is not clear whether the same effect can be obtained on the moon, which has a low gravity. Wells and colleagues have applied for a separate grant for additional experiments looking at effects in microgravity. Future experiments will further clarify whether liquid nitrogen is suitable for washing spacesuits.
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Text: Riri Ayae
