Can one survive 10 seconds on the moon without a spacesuit helmet?
October 26, 2009 11:08 AM   Subscribe

What would happen if spacesuit helmet was removed for 10 seconds on the moon?

Despite all unlikelihood, consider this hypothetical situation: An astronaut stands on the moon. He currently has no access to any form of shelter --aside from his space suit. He is on the brink of starvation. If he can stay alive a little longer he will be rescued, but he must eat to do so. He has food rations in hand. Assuming he must unseal/unfasten his helmet to ingest the food, could he do so and survive?

If no one is certain how long it might take an astronaut to make such a maneuver, let us hazard a guess that the whole process would take no longer than 10 seconds.

What would be the affects of depressurization and the subsequent exposure to the vacuum of space within this 10 second time frame.

Also, would the space suit return to its previous functioning state afterward?
posted by swiffa to Science & Nature (22 answers total) 30 users marked this as a favorite
It would not be smart, but NASA estimates that a 30 second exposure to vacuum (which the moon is near as) would not cause permanent injury.

An interesting question is how long before one passes out in vacuum. Estimates range from 15 seconds to 30 seconds.

Tens seconds might be ok, but it would be very brutal.
posted by bonehead at 11:12 AM on October 26, 2009 [3 favorites]

Another reference, indicating the time of useful consciousness is 9 to 12 seconds. Your man is right on the edge.
posted by bonehead at 11:14 AM on October 26, 2009 [1 favorite]

While the links others have posted indicate that someone could SURVIVE in the vacuum in that long, I'm not sure it takes into account eating.

The problem with eating is that your body tries to take in air when you eat and I'm not sure how that would work in the vacuum and whether you could even get any food down.

In general, I'd say that the person would be better off with the risk of starving than the risk of dying due to decompression.
posted by Elminster24 at 11:21 AM on October 26, 2009

In the practical sense, it really seems like he just needs to get the rations into his helmet, then he could surely get them into his mouth somehow, even without the use of his hands.

Helmet off, toss rations into mouth, helmet back on. Surely the total exposure is less than ten seconds. Less than five even if he's quick with the snaps/buttons/lock collar/whatever.

He would also likely suffer some brutal frostbite on his face.
posted by dnesan at 11:26 AM on October 26, 2009

He would also likely suffer some brutal frostbite on his face.

Well, a vacuum would insulate the face and the only skin heat loss would be due to thermal radiation. I'm skeptical that there would be any frostbite or that one would even feel cold, at least at first.
posted by crapmatic at 11:37 AM on October 26, 2009 [1 favorite]

People freezing in space is an old movie cliché. There is nothing there to suck away the heat, so the astronaut will lose body heat through radiant heat loss only, assuming a near-vacuum, and this takes time.

Frost bite will not be an issue.
posted by metacollin at 11:39 AM on October 26, 2009 [3 favorites]

I think the most unlikely part of this scenario is that the astronaut could get the helmet back on in under 5 seconds.

I suspect that putting the helmet back on, in space, would be more difficult than putting a lens on an SLR camera, in the dark, while wearing work gloves.

If suit gloves remain pressurized, our hero is not going to have great dexterity. Even if the suit is unpressurized, the astronaut is still is trying to mate a fishbowl to an airlock while wearing gloves, lining things up partly blind as they can't see the entire collar or helmet.
posted by zippy at 11:44 AM on October 26, 2009 [1 favorite]

The pressurization system of the suit would probably play a large part in the survivability of the attempt. If the astronaut didn't have a way to disable it temporarily it would likely be exhausting air continuously while the suit was breached in an attempt to restore adequate pressure; this would result in a powerful flow of air out of the neck/faceplate of the suit that might complicate attempts to just toss the ration pack in there. Blasting all that air out of the storage tanks would also likely cause a precipitous drop in the available breathing supply, especially if the suit uses a rebreather system and has a limited supply of breathable air to begin with.

Wikipedia's got some information on the operating pressure of space suits and the survivability of vacuum exposure (they say consciousness is retained for 15 seconds.)
posted by contraption at 11:45 AM on October 26, 2009

First thing to happen: WHOOSH! All the air is sucked out of your guy's lungs. After that, maybe he can jam some food into his face. Not sure if his throat tissues would dehydrate very quickly, but that could be a factor. Can't swallow with a dry throat.

Water would be a bigger necessity for him. You can live without food a lot longer than you can live without water.

Any decent spacesuit would have emergency rations, though, right? I guess he's gone through these.

There is a good fictional study of similar cirumstances. Heinlein's Have Spacesuit, Will Travel. It's dated, sure, but has some interesting ideas about how spacesuits should be designed. Thinking has changed a lot since then but it's still worth reading.

More here on spacesuits in fiction
posted by Guy_Inamonkeysuit at 11:46 AM on October 26, 2009 [1 favorite]

One of the trickier aspects of this is whether to depressurize the suit slowly or rapidly. If you do it slowly, you make the whole procedure longer and risk passing out before it's finished. But if you depressurize the suit rapidly (less than 1 second), you risk fatal lung damage, especially if you try to hold your breath.

NASA studied the effects of explosive decompression of pressure suits way back in the 60's and the results are in NASA CR-1223 (100+ page scanned PDF), in case you want to read about this in excruciating detail.

As to whether or not the suit would return to normal operation afterwards... in order to have already survived long enough for starvation to be a factor, your hypothetical astronaut must have been in that suit for a long time (days or weeks). That implies a large amount of gas on board to make up for small leaks, at the very least. And much more if the suit simply supplies fresh oxygen and dumps the exhaled CO2. So repressurizing the suit should require only a tiny fraction of the gas carried.
posted by FishBike at 11:47 AM on October 26, 2009


Good point. The 9-12 second number assumes that our Hero can depressurize non-explosively. An explosive decompression is estimated to halve the working time to 5s of consciousness (see the Landis link above). If he can only open his helmet in a sudden release of pressure, the astronaut is probably a goner.
posted by bonehead at 11:49 AM on October 26, 2009

The late science fiction author and physicist Charles Sheffield wrote a bit about this, positing that, as space travel became slightly more popular, future astronauts might be trained down to a reflexive level with the "Sturm Invocation," similar to the way some military recruits are trained to understand why gas masks are useful. The fictitious routine would be a way of creating near-involuntary survival behaviors enabling astronauts to survive a brief exposure to vacuum should circumstances be desperate enough to require it. From a critical scene in The Compleat McAndrew Chronicles:

The sensation was strange. I still had full command of my movements, but a new set of involuntary activities came into play. Without any conscious decision to do so I found that I was breathing hard, hyperventilating in great gulps. My eye-blinking pattern had reversed. Instead of open eyes with rapid blinks to moisten and clean the eyeball, my lids were closed except for brief instants. I saw the lock and the space outside as quick snapshots. The Sturm Invocation had the same effect on McAndrew, as his own deep programming took over for vacuum exposure. When I nodded, he swung open the outer lock door. The air was gone in a puff of ice vapor. As my eyes flicked open I saw the capsule at the top of the landing tower. To reach it we had to traverse sixty meters of the interstellar vacuum. And we had to carry Sven Wicklund's unconscious body between us.


From doing research myself and from bits of interviews, I gather that Sheffield was a guy who did his homework, so take that as you will.
posted by adipocere at 11:51 AM on October 26, 2009 [10 favorites]

Just for reference: I'm trained with, and sometimes help with the training for, HAZMAT suits (a Level A suit, technically). These are regulated-supplied air SCBA masks with non-transmissive suits, not completely unlike a space suit. There's no way I'd attempt this with an SCBA mask. It takes about 15 minutes to put one on, at least 10 minutes to fit the mask and go on air with an SCBA. It might take me ten seconds to fit my hose to the regulator and go on air---you have tp do it in the space of one held breath.
posted by bonehead at 11:57 AM on October 26, 2009

Given those NASA estimates it seems plausible that a reasonably healthy and able-bodied person could get a helmet off, stick some food in their mouth, and get the helmet back on before passing out. Wouldn't be fun, but may be possible.

People "on the brink of starvation" are not reasonably healthy and able-bodied, though. The human body can go a loooong time without food. But starvation becomes critical relatively quickly, to the point where I don't think it's remotely plausible that our moon man's situation would be so dire that he would need to eat food or perish before rescue, yet be physically able to get the helmet off and on quickly enough and get food into his mouth.

He'd have to know that rescue was coming but in some long-enough time that he was willing to do the risky vacuum feeding maneuver while still physically capable.
posted by 6550 at 12:03 PM on October 26, 2009 [1 favorite]

He'll probably suffocate before he starves, as the oxygen supply in the suit will surely deplete before he gets hungry.

But astronauts tend to be very clever and resourceful. Note that the helmet is usually pressurized separately from the rest of the suit, so he does not need a full shelter, just something that can protect him neck-up. Finally, assuming he has a steady supply of oxygen from some outside source, then he isn't completely destitute, and he has some equipment on hand.

He will only need to do create some contraption that can equalize the pressure enough so that he can endure opening his helmet (not necessarily completely removing it) for long enough to get food in there. He does not need a full shelter, just a temporary head shelter.

Just thinking out loud. Your astronaut seems pretty screwed, though.
posted by jabberjaw at 12:13 PM on October 26, 2009 [2 favorites]


If he's that close to dying from starvation, he probably won't have the strength to do all of this in 10 seconds.
posted by Brandon Blatcher at 12:29 PM on October 26, 2009 [2 favorites]

Here is what Nasa says:

How long can a human live unprotected in space?






posted by Damn That Television at 1:08 PM on October 26, 2009 [19 favorites]

[Clemency granted. If you want to discuss the appropriateness of the question, go ahead and do so in this metatalk thread, and stick to answers in here.]
posted by cortex at 2:41 PM on October 26, 2009 [1 favorite]


This depends on whether this sort of situation has been anticipated and/or if has been done before.

The Apollo 1 accident, which killed three 3 astronauts, happened because of a number half assed and terrible design situations were done. The wiring of the craft was shoddy, they were working in a pure oxygen atmosphere and the escape hatch required a special wrench and a long time to open.

After these problems were highlighted in the investigation afterwards, numerous design changes were made, some of which are credited with enabling the Apollo 13 astronauts to survive. So whether the suit would still work really depends on the design of the suit and the knowledge of the designers, which often comes after accidents have occurred.
posted by Brandon Blatcher at 3:56 PM on October 26, 2009 [1 favorite]

Most space suits helmets have a valve that you can ram a special straw through to drink some food-paste or water.
posted by OldReliable at 4:02 PM on October 26, 2009

My understanding is the same as OldReliable's, that the helmets have an input port and that food-paste and water are made to be compatible with it. If you're writing a story, you should look into this to be sure you're not setting up your guy in a scenario (having like a granola bar rather than packets of food goo with straws) that wouldn't happen.

Here's an interview with a company that makes space suits - thier description is different from what I'm remembering. Maybe the suit I'm remembering is an older model, or one that they only wear within the ship?
INSKEEP: Now you mentioned that you need to provide everything that an astronaut would need for up to eight hours in space at a time. The obvious requirement is oxygen, but what else is there?

Mr. FRANCIS: Well, water, food. They do have a small snack that they can actually eat that's inside the helmet. We actually...

INSKEEP: How do they get at that?

Mr. FRANCIS: Well, it's basically on the side of the helmet and they have to move their head inside the helmet to eat it. Maybe not so obvious, one of the things you can't do is you can't get your hand inside the helmet, so you have to be able to move your head to drink. You have to be able to move your head to eat.

INSKEEP: What's the snack?

Mr. FRANCIS: You know, I don't--it's like an energy bar-type thing. I don't--I've never had one myself, so I can't tell you exactly what it is, but..

INSKEEP: I would think, you know, as the vice president and general manager of the company, they'd make you eat a few of those.

Mr. FRANCIS: Well, we don't make the snacks. We just make the suit.

INSKEEP: And I guess it's probably not in a wrapper or anything like that. Little problem.

Mr. FRANCIS: No, a wrapper on the snack would be a real problem. But we do provide water. We also, obviously, have to provide to remove the water from the environment. You know, otherwise, humidity would build up on the inside of the helmet.
A few related previous questions that might be useful:
-can humans survive in the vacuum of space for 10 seconds with only thermal wrap? (lots of good links on this one)
-what would happen if I stuck my naked hand into the vacuum of space?
-what happens after you're thrown out the airlock into space?
-surviving in the vacuum of space
-the smell of space
posted by LobsterMitten at 6:26 PM on October 26, 2009 [2 favorites]

another related previous question -
what would happen if I were put on the moon with no spacesuit?
posted by LobsterMitten at 7:37 PM on October 26, 2009

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