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Wouldn’t it be easier to make a space suit that only maintains air around the head, and just has a “tight” insulated and shielded suit around the body?

It seems to me the reasons we need a space suit are:

  1. To breathe
  2. To be protected from the low pressure of vacuum
  3. To be protected from radiation
  4. To be protected from extreme temperatures (hot and cold)

Only the first requires air. The biggest challenge that was faced in designing the original space suits was that air wants to distribute pressure evenly, causing the suits arms and legs to spread out and not bend easily. This is still a major design challenge that leads to clunky joints all over the suit. Metal joints on the new suit announced by NASA don’t look much better.

Would it work to just have air within the helmet on the head of the astronaut, with a suit that is like a wet suite with enough tension to have the equivalent pressure of one atmosphere on the body? Wouldn’t this give much more flexible design constraints to suits and what an astronaut could do?

I feel like I’m missing something fundamental, but can’t think what it would be.

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    $\begingroup$ We sweat continuously and generate solid and liquid waste regularly, so there's those to contend with in some way or another, but see also What ever happened with that pressure suit design based on elastic tension in contact with skin? $\endgroup$ – uhoh Dec 5 '19 at 7:03
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    $\begingroup$ A thin layer of air would help enormously with insulation (your reason #4), but actually the problem isn't insulation (vacuum is a already an excellent insulator), but removing excess metabolic heat. $\endgroup$ – Martin Bonner supports Monica Dec 5 '19 at 8:28
  • $\begingroup$ @MartinBonnersupportsMonica don't some suits contain a water-cooled garment in contact with the skin? I'm not sure if bodies always need to be air-cooled. $\endgroup$ – uhoh Dec 5 '19 at 10:35
  • $\begingroup$ Ok, only the first requires air, but maybe alone this is an enough strong reason to have air in them? :-) $\endgroup$ – peterh - Reinstate Monica Dec 5 '19 at 11:21
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    $\begingroup$ You should read about capstan partial pressure suits that are used a lot in aviation. However from what I read it seems that they are quite nasty to wear in the depressurized environment longer than 30 minutes. So I think that you can find answer to your question reading about the experience with such suits $\endgroup$ – OON Dec 5 '19 at 14:22