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In the period when the Crew Dragon Demo-2 mission was initially docking with the ISS, before the hatches were open, one of the tasks was to "dry the suits". They reported on the status later, indicating they had been drying for over an hour.

Is that to remove humidity from wearing the suits? Or some other reason?

Sorry, I can't get timestamps, but it's while docked and (only) the first hatch is opened.

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    $\begingroup$ After more than 19 hours in the suit there will be not only sweat within the suit. In zero gravity simple duties may take more time. $\endgroup$
    – Uwe
    May 31, 2020 at 20:15
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    $\begingroup$ different but related: What does the interior of a spacesuit smell like? and Current and near-future space suit odor reduction technology $\endgroup$
    – uhoh
    May 31, 2020 at 20:27
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    $\begingroup$ indeed @uwe - though they weren't wearing it for the full 19 hours. On the other hand, they were wearing it many hours before launch. $\endgroup$
    – tedder42
    May 31, 2020 at 20:40
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    $\begingroup$ Humans sweat. It's what we do. Sweating however is not that good for spacesuits. $\endgroup$ Jun 1, 2020 at 4:37

2 Answers 2

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To clean them

Would you like to wear something for days on end with the suit being wet, disgusting, and dirty? No, of course not. Just like clothes are cleaned on Earth, so are they in space.

It can hinder the functioning of spacesuit

Water can, if in enough quantity, can cause problems. When water leaked during a spacewalk, it didn't go to well. Nor would it be great if sweat and dust was allowed to continue to stay there.

There may be other reasons, but these issues certainly play a major role in SpaceX decisions to use time for drying the suits.

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    $\begingroup$ Okay, that is fair i have fixed that @uhoh $\endgroup$ Mar 16 at 21:39
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    $\begingroup$ You commented that the other answer is "unsourced nonsense," but your answer is also unsourced. Your linked news article only supports the assertion that water leaks inside EVA suits can be problematic, not any of the rest of your answer, which is essentially the same content as the comments on the question from three years ago. Sources need to support claims. If you'd sourced "just like clothes are cleaned on Earth, so are they in space" you'd find most of the clothes on ISS are thrown out, not cleaned. $\endgroup$
    – Erin Anne
    Mar 17 at 22:23
  • $\begingroup$ My answer isnt nonsense at least @ErinAnne $\endgroup$ Mar 17 at 22:48
  • $\begingroup$ And most but not all i am talking about those that are cleaned as that is the question @ErinAnne $\endgroup$ Mar 17 at 22:57
  • $\begingroup$ Drying being part of the cleaning process is something you're asserting in your answer, unsupported. $\endgroup$
    – Erin Anne
    Mar 17 at 23:03
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The human body is an incredible source of moisture. When you climb into the suit, the body is most of the volume of the suit with a smaller amount of surrounding air. The compressed air in the tanks is generally quite dry. So now the suit is closed, and these three elements (person, extra air, tank air) mix and search for equilibrium.

So dryer air goes into the lungs, which are near 100% humidity and you then you exhale very moist air.

https://www.npr.org/sections/krulwich/2013/06/19/193556929/every-night-you-lose-more-than-a-pound-while-youre-asleep-for-the-oddest-reason

“As we exhale, our body moistens the surfaces of our lungs and the air we exhale, now warmed to approximately 90F has a relative humidity of almost 100%. At 90F and 90%, each gram of dry air we exhale (that is, the air we exhale minus the weight of the water vapor in it) also carries with it 0.0272 grams of water vapor.”

In very short order, the air surrounding the person is near 100% humidity and there is a very limited ability to remove moisture. The internal surfaces of the suit get wet, because there has been nowhere for the moisture to go.

So yes, there is a priority to get the additional moisture out of the suit.

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    $\begingroup$ Do you have any sources that confirm the SpaceX IVA suits in question actually get near 100% humidity? They're umbilicaled to the spacecraft, so they're not really a closed system as far as air goes. $\endgroup$
    – Erin Anne
    Mar 17 at 7:36
  • $\begingroup$ The question was “Why do we need to dry the suits”. My point was that humans continually expel moisture by exhaling. There were earlier points about sweating, and I don’t imagine that is a problem. We know the suits are temperature controlled and there’s not a lot of exertion going on. The exhaled moisture is constant and unavoidable. It’s entirely possible the ship is exchanging air with the suits, but we know about the drying step, so clearly more drying is required. $\endgroup$ Mar 17 at 20:42
  • $\begingroup$ @AnthonyStevens you assert "so now the suit is closed" to make your point in the answer. The suit isn't closed, and moist air is likely being carried out and dealt with by the capsule's air conditioning systems before being replaced by drier air. You being convinced that sweat isn't the problem (why?) so humid exhalation must be instead is fine, but you should support that with something. $\endgroup$
    – Erin Anne
    Mar 17 at 22:21
  • $\begingroup$ This is great discussion. I just want to point out that the question is not a Dragon systems question. It’s about the suit and moisture in the suit and processes to remove moisture from the suit. Maybe I’m off base too. I bet there are many sources for moisture to build up in the suit. There is a pretty good stretch of time where the astronauts are suited but out of the Dragon, generally with the visor open. That must be fun in Florida. Maybe one day, we’ll get a walk thru documentary, I know I’d watch it. $\endgroup$ Mar 18 at 2:36

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