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How do astronauts walking on the moon keep their waste body fluids from freezing in the extremely cold environment? I understand that if they need to release waste body fluids, they do so into specifically prepared "diapers" or some other such system. But still, all body fluids, such as blood, cranial, urinary, etc., must be kept at warm enough temperature to flow. How is this done? Are radioisotope heat generators used in any way?

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The challenge of keeping an astronaut in a suit on the moon comfortable turns out to be in keeping him cool, not keeping him warm.

Heat is transferred in three ways: (infrared) radiation, conduction (direct contact), and convection (transfer via a fluid medium like air). For a suited astronaut, conduction is minimal and convection is nonexistent; the only way the suit loses heat is by radiating it. The exterior of the suit is white to minimize heating in direct sunlight, but that also minimizes radiative ability. So all the heat produced by the astronaut's body in the suit stays in the suit, and that's a substantial amount.

So you actually have to circulate coolant through tubes in an undergarment of the space suit to draw heat out. Freezing urine is not at all a concern!

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  • $\begingroup$ Links to Wissler and 41 node models would be appreciated :) Merry Christmas everybody. $\endgroup$ – Deer Hunter Dec 25 '14 at 19:50
  • $\begingroup$ That is, during the lunar day. Going out at night is very cold indeed and would probably be avoided. $\endgroup$ – kim holder Dec 26 '14 at 0:53
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    $\begingroup$ I don't think that's the case -- again, you only lose heat via radiation, and the suit is well insulated, with a 100-watt human inside. $\endgroup$ – Russell Borogove Dec 26 '14 at 1:48
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    $\begingroup$ @RussellBorogove maybe it is cooler at night - I heard that this is the main reason they land on the sun at night too. :) $\endgroup$ – uhoh May 8 '16 at 14:35
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    $\begingroup$ en.wikipedia.org/wiki/Primary_Life_Support_System "[PLSS] circulated water in an open loop through a Liquid Cooled Garment, expelling the water into space, where it turned to ice crystals. Some of the water was also used to remove excess heat from the astronaut's breathing air, and collected for dumping into the spacecraft's wastewater tank after an EVA." $\endgroup$ – Russell Borogove May 9 '16 at 2:27

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