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@GremlinWrangler's answer to How can an Astronaut survive for six days inside a Spacesuit? includes the following:

make sure the suit can provide air and water, and adjust the temperature to minimize calorie consumption and then just wait and let body go into survival mode.

Question: What's the best (least worst) temperature to expose an astronaut to, to minimize calorie consumption and/or to make them the most comfortable while spending six days inside a space suit in "survival mode"? If I understand correctly, they aren't floating naked in the air inside the suit, but instead wrapped with something, possibly the liquid cooling system, so I'm not even sure which temperature I'm asking about; the astronaut's skin temperature, or the liquid, or the air.

uhoh
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    The best temperature for a 40 kg female and a 90 kg male astronaut may be different. Surface to volume ratio is different and also the ratio of body fat to muscles. – Uwe Oct 23 '19 at 10:50
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    I suspect the data on this would come from care instructions of hunger strikers, but not planing to go searching down that rather depressing rabbit hole. Would suggest your question is about skin temperature, you want to hold it at the point that the (greatly slowed) critical metabolic processes are enough to keep the core at 37c on waste heat without additional energy being burned. Ideal will probably involve different temperatures for limbs, core and possibly head. – GremlinWranger Oct 23 '19 at 10:52
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    Somewhat related: Apollo allowed for a 115 hour contingency return scenario where the crew had to stay in the suits that long. https://space.stackexchange.com/a/33883/6944 – Organic Marble Oct 23 '19 at 15:26
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    For six days in a survival situation food is unimportant so long as the temperature is reasonable. – Loren Pechtel Oct 24 '19 at 05:27
  • @LorenPechtel That's a great point! Except for the unpleasant effects, not eating (and therefore not producing additional solid waste) is probably a good thing. – uhoh Oct 24 '19 at 08:37
  • @uhoh Also, if you're in a water-limited situation you should not eat even if you have food. Digesting and metabolizing food costs you water and thus shortens your survival time. – Loren Pechtel Oct 25 '19 at 03:13
  • @LorenPechtel that's a great point as well! Should I eat when I don't have anything to drink in a survival situations? – uhoh Oct 25 '19 at 03:20
  • It’s probably better to pick a heart/respiration rate than a fixed temperature. My concern is sleep. You can’t not sleep for 6 days, you will go psychotic. Waking from sleep could be a real problem. Better to adjust temperature, aiming for a certain heart rate. You could build in sleep and wake cycles. – Anthony Stevens Jun 17 '20 at 12:53

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Interesting question! My answer would be 30 ∘C, it’s the center of the moderate hypothermia range. That range has symptoms we would be looking for (slow heart and breathing) and a few symptoms that could cascade into death, but not immediately.

Further explanation:

Hypothermia has 3 medically defined core temp ranges, mild (33–35 ∘C), moderate (28–32 ∘C), severe (24–28 ∘C). Below 24 ∘C), the experts agree will kill you.

The symptoms of each range is:

enter image description here

Seems like the moderate range of 28-32 ∘C is bad, uncomfortable, but not quickly fatal. The mild range seems pretty long term survivable, the severe range seems quickly fatal.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5680406/

https://www.betterhealth.vic.gov.au/health/healthyliving/hypothermia

Anthony Stevens
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  • Hypothermia relates to the body's core temperature and not to the surrounding temperature. I know I have felt excruciatingly hot when the surrounding temperature was near 30C or 86F. That may not be cold enough because the body still generates heat and has to reject it to maintain 37C. – aranedain Jun 17 '20 at 15:13
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    You can’t have it both ways. The goal is to slow metabolism. They will make heat, but less. In addition, these astronauts need to avoid movement for 6 days to conserve calories. The only other alternative is a fever, and under these conditions their health would deteriorate rapidly. – Anthony Stevens Jun 17 '20 at 15:50