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At various moments in the NASA video NASA’s SpaceX Crew-3 Astronauts Launch to the Space Station astronauts are shown standing or walking or otherwise posing for the camera in their Dragon capsule suits without any connection to a water cooler/recirculator that would normally pump coolant through a system of tubes in thermal contact with the astronauts body to remove the one to several hundred watts of heat the human body produces under various levels of exercise.

Even in the early days of spaceflight astronauts carried portable cooler/recirculator units. Here are some more recent examples:

So I assume that in the screenshots below the astronauts were only momentarily disconnected from their units, which they probably anxiously eyed the whole time as they would have started getting toasty almost immediately.

Question: How long can astronauts wearing Dragon capsule suits walk around unconnected to water coolers?

I'm not asking for an LD50 answer (i.e. how long before half of them would die) but more of a rules and/or comfort answer. Like everything else there are likely stated limits on how long they are allowed remain disconnected, and limits on the amount of physical exercise they can do while being disconnected.

There may also be at least a lower limit that can be gleaned from video; if they're shown disconnected continuously for 90 seconds for example then an acceptable answer might be "apparently at least 90 seconds."


These "hotshots" must have been getting pretty hot, literally!

screenshot from the NASA video NASA’s SpaceX Crew-3 Astronauts Launch to the Space Station https://www.youtube.com/watch?v=zekfpIRlVyY showing them disconnected from their portable coolers screenshot from the NASA video NASA’s SpaceX Crew-3 Astronauts Launch to the Space Station https://www.youtube.com/watch?v=zekfpIRlVyY showing them disconnected from their portable coolers

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    $\begingroup$ In case anyone wants to get out their stopwatches: the Teslas are modified to have a Dragon-compatible suit connector in the back seats, so the astronauts are "plugged in" while they are in the Teslas. I can't remember whether they use portable packs on the tower, but I think the answer is "at least as long as the time from exiting the Teslas to capsule ingress of the last crew member". $\endgroup$ Jan 1 at 11:39
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    $\begingroup$ Do we know that liquid cooling garments are worn under the Dragon capsule suits? $\endgroup$
    – Uwe
    Jan 1 at 16:26
  • $\begingroup$ @Uwe not an answer, but I think we at least know that they're not worn over them :-) $\endgroup$
    – uhoh
    Jan 2 at 1:05
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    $\begingroup$ On one hand, water heat capacity means heating the coolant to problem temperatures by body heat alone can take a fairly long time. On the other hand, weather will have a significant impact - especially intense sun exposure may reduce the time significantly, while cold, cloudy weather could extend it indefinitely - or even shorten it due to heat loss. $\endgroup$
    – SF.
    Jan 2 at 4:02
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    $\begingroup$ The stylist thought that the briefcases were ugly so they had to do without. $\endgroup$
    – Innovine
    Jan 2 at 9:24
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There may also be at least a lower limit that can be gleaned from video; if they're shown disconnected continuously for 90 seconds for example then an acceptable answer might be "apparently at least 90 seconds."

"Apparently at least 1009 seconds, as seen during the Inspiration4 mission".

In the Crew-3 video, NASA unfortunately did not show the astronauts leaving the Teslas nor do we get video from inside the capsule as the umbilicals are connected (we do get video of Matthias Maurer taking his seat, but unfortunately, his right leg with the umbilical port is obscured from the camera), so we don't have an exact number:

  • At T-02:51:45, Raja Chari enters the frame, so he must have left the Tesla at some time prior to that.
  • At T-02:51:38, Thomas Marshburn enters the frame, so he must have left the Tesla at some time prior to that.
  • At T-02:51:33, Matthias Maurer and Kayla Barron can be seen in the background outside the Teslas, so they must have left the Teslas at some time prior to that.
  • At T-02:37:43, Matthias Maurer is the last crew member to ingress into the Dragon capsule. NASA is not showing any video from inside the spacecraft, so we don't know exactly when his umbilical is connected. We can see through the window that he is not in his seat until at least T-02:37:32.
  • It looks like T-02:36:38 may be the point where pad ninja 22 connects the seat 4 umbilical to Matthias Maurer's suit.
  • At T-02:36:31, Matthias Maurer does his first informal communications check through the umbilical, so at this point, he is definitely connected.

This gives us a number of "at least 813 seconds with a pretty wide margin of error". During ingress, we can hear a callout that they are 2 minutes ahead of schedule, so it stands to reason that the suits are rated for at least another couple of minutes without umbilical support.

For Inspiration4, SpaceX and the crew gave a lot more media access than NASA does, so we have a very precise timeline:

  • At approximately T-02:59:06, we see Jared Isaacman exiting the right side of the left Tesla.
  • At exactly T-02:42:17, we see Pad Ninja 7 plugging in Jared Isaacman's suit umbilical. Jared Isaacman was the last crew member to ingress Dragon and one of the first to exit the Teslas, so he was the one who wore his suit the longest without being connected to the umbilical.

It looks like during a nominal mission, the crew will be without umbilicals for close to 20 minutes. However, in a worst case scenario, they still must be able at this point to walk to the escape slides, slide down to the ground, and walk to the bunker before they have a chance to doff their suits.

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The human body contains 50 to 70 % of its mass of water. Lets assume an astronaut of 80 kg with 50 kg water.

How much heat energy is needed to raise the body temperature by only 0.5 °C? The energy to raise the temperature of 1 kg water by 1 °C is 1 kcal or 4.184 kJ. For 50 kg and 0.5 °C it is 25 kcal or 104.6 kJ. I assume the heat production of the body with 200 W.

How long does it take to heat 50 kg of water by 0.5 °C with 200 W of heat production? 1 Joule is 1 Watt second. So the time 104.6 kWs / 200 W = 523 seconds or 8 minutes and 43 seconds.

I did not consider the heat loss by breathing, the exhaled air is leaving the body with a temperature of about 37 °C and 100 % humidity. The heat needed for the 30 kg dry mass of the body was not considered. The temperature of arms and legs is normally lower than the body core temperature of 37 °C, its about 34 °C.

So about 20 minutes within a suit without cooling seems possible.

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  • $\begingroup$ This is excellent, a first-principles answer! There are situations where people get wrapped in plastic wrap for cosmetic treatment (and other) reasons for periods of time, so apparently this is not as instantly unbearable as I'd originally thought. $\endgroup$
    – uhoh
    Jan 2 at 0:48
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    $\begingroup$ If they are inhaling ambient temperature air, that will provide enough cooling for survival(but extreme discomfort) indefinitely. Same as how you can wear a full arctic parka in a room temperature department store for hours, and the problem is dehydration from sweating, not total thermal exhaustion. Inhale dry air at 21C, exhale at 38C, and you are dumping 100w by convection and 50w by evaporation in the lungs. (and yes, this puts the body at about 39C. A nasty fever, but you can function) $\endgroup$ Jan 2 at 8:43

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