This excellent answer to How have space suits dissipated the heat removed from astronauts? shows a diagram including the sublimator unit in the red square where the phase transition of water from solid/liquid (it may be "slushy" at this point) to gas removes the heat produced inside the suit the astronaut to avoid overheating.

I've never seen an actual "sublimator opening" where this happens.

Question: Where exactly are the Apollo space suit sublimators that vent steam1 into space? is there a photo of an astronaut in space that shows the opening?

1The old documents say "steam" and of course that's what water vapor can be called. It won't look "steamy" because it's not condensing into visible droplets; molecules are flying off at 300 to 400 meters/second on ballistic trajectories. If it was in air, the molecules would be bouncing around and diffusing away and constantly colliding every dozen microns or so, so that they have plenty of opportunities to form droplets.

Buzz Aldrin carries the EASEP

above: "Buzz Aldrin carries the EASEP." from here

I don't see an opening in the white fabric cover of Armstrong's system in the photo above. How/where does the steam get out?

update: See Figure 15, page 15 in The Apollo Portable Life Support System By Kenneth S. Thomas

Figure 15 Apollo’s Second Generation PLSS (Courtesy United Technologies Aerospace Systems)

Figure 15 Apollo’s Second Generation PLSS (Courtesy United Technologies Aerospace Systems)

Apollo space suit life support system click for larger



1 Answer 1


It can be hard to see because it's on the front of the PLSS behind the astronaut's helmet.

enter image description here

(NASA photo of Irwin on Apollo 15, I cropped it and added the arrow)

Here's an exploded view showing the vent opening; the sublimator isn't labeled, but it's clearly the same device labeled in the image in the question.

enter image description here

From Apollo EMU Experience Report, I added the arrows.

It appears the size and shape of the vent varied from generation to generation of the PLSS.

enter image description here

enter image description here

Last two images from

The Apollo Portable Life Support System

  • 7
    $\begingroup$ In a million years it never would have occurred to me to think to just look on the other side :-) $\endgroup$
    – uhoh
    Commented Jun 13, 2021 at 17:08
  • 4
    $\begingroup$ That's what stack exchange is for, I guess :) It was hard to find an inflight picture where you could see it. $\endgroup$ Commented Jun 13, 2021 at 17:09
  • $\begingroup$ A pretty amazing find it is! Did you know it was there and just straight-off start looking or the right angle, or did you have to track down where it was first. I could have sworn it was on the back at the bottom for some reason, like the radiators on an old refrigerator. $\endgroup$
    – uhoh
    Commented Jun 13, 2021 at 17:41
  • 3
    $\begingroup$ Yeah, I knew where it was and started plowing through google image search to find a picture where it was visible. Then I tried to find a schematic drawing where it was actually labeled, but no joy on that. $\endgroup$ Commented Jun 13, 2021 at 17:43
  • 2
    $\begingroup$ @organic therebreathersite.nl/03_Historical/apollo_rebreathers.htm Has a diagram with it labelled, about 1/3 of the way down 🙂 $\endgroup$
    – Tim
    Commented Jun 15, 2021 at 9:23

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