Would an astronaut survive burial on the Moon?

[Peter B]

There's a plot point in a novel (I won't mention it in case you haven't read it) which relies on astronauts hiding from enemies by being buried under the lunar soil.

Would it be possible to do that with an Apollo-style space suit? Would it affect something like the suit's sublimator, or simply cause the astronaut to overheat in a few minutes? Or is it something which would be survivable for several hours with a minimum of improvisation?

[Allan F]

As long as the sublimator wasn't blocked, and the sun wasn't at a high angle, the possibility could exist. But how easy it would be to bury somebody there, and hide the tracks leading there, that's another story.

[ka9q]

A space suit is already excellent thermal insulation so you won't make yourself any hotter with burial. But for the same reason you must have continuous active cooling, so the sublimator would have to be vented to vacuum and kept supplied with feedwater.

If they couldn't find you by your tracks or disturbed soil, they could look for the cloud of water vapor coming from your sublimator. It wouldn't be visible but it would be readily detectable with instruments.

[Allan F]

If the sun was high on the sky, the soil would be heated, and you'll get some conductive heat transfer.

[BazBear]

I have to admit that the first thing that popped into my head, after reading the thread title, was the old misdirection joke "a plane crashes right on an international border, where do they bury the survivors?".

[Allan F]

I have to admit that the first thing that popped into my head, after reading the thread title, was the old misdirection joke "a plane crashes right on an international border, where do they bury the survivors?".

"In Russia, a helicopter crashed in a graveyard. So far, 112 people has been found dead."

[Peter B]

Thanks folks, that was more promising than I expected.

Regarding the telltale tracks, that was unlikely to be an issue. The astronauts were buried at locations marked with coloured rocks. The bad guys saw the coloured rocks but assumed they were something to do with a science experiment (which seemed reasonable to me), so there would be nothing suspicious about seeing tracks. Given the way the Apollo astronauts managed to obscure their tracks, I imagine it would be relatively easy to disguise the number of people walking around to minimise any suspicions of "two went in but only one came out".

Regarding the detectability of water vapour, that might have been a little less reasonable. You'd think the bad guys might at least be expecting an ambush, so might have some sort of IR device which would presumably reveal the water.

Finally, ensuring access to vacuum for the sublimators, might also have been tricky. The story makes it seem like they were simply lying in holes in the ground and got covered up. If it was necessary to insert a pipe into the soil or leave a little hole to ensure part of the sublimator was uncovered, then presumably that would have had the potential for being noticed by the bad guys...

Still, it was a ripper scene in the novel (from a time when the author wrote OTT but still just about plausible thrillers).

Thanks folks.

[Allan F]

How much water vapor was there? How much did they carry for an 8 hour EVA? And did the exhaled water vapor get used?

[Trebor]

5 litres of water

See Wikipedia page for more details :
http://en.wikipedia.org/wiki/Primary_Life_Support_System

[ka9q]

How much water vapor was there? How much did they carry for an 8 hour EVA? And did the exhaled water vapor get used?

Only the feedwater in the tank went through the sublimator into space. Condensation from the suit gas loop was stored and later dumped. I guess it couldn't be used for evaporation (simulating what happens in normal perspiration) because some sweat might have gotten in there and clogged the sublimator pores.

Water is one of the most valuable substances imaginable on the moon, so expending it just to cool a spacesuit does seem rather wasteful. It worked for short Apollo stays, but a permanent base will require something more sustainable.

[Noldi400]

How much water vapor was there? How much did they carry for an 8 hour EVA? And did the exhaled water vapor get used?

Only the feedwater in the tank went through the sublimator into space. Condensation from the suit gas loop was stored and later dumped. I guess it couldn't be used for evaporation (simulating what happens in normal perspiration) because some sweat might have gotten in there and clogged the sublimator pores.

Water is one of the most valuable substances imaginable on the moon, so expending it just to cool a spacesuit does seem rather wasteful. It worked for short Apollo stays, but a permanent base will require something more sustainable.

Indeed. I seem to remember a comment somewhere in one of the documents that water (for cooling) was one of the most time-limiting factors on the lunar missions, much more so than oxygen.

[Morgul]

Just curious, is it a Clive Cussler book?  That bit sounds familiar.

[Peter B]

Just curious, is it a Clive Cussler book?  That bit sounds familiar.

Congratulations. One virtual banana for you. :-)

[ka9q]

Indeed. I seem to remember a comment somewhere in one of the documents that water (for cooling) was one of the most time-limiting factors on the lunar missions, much more so than oxygen.

The consumables (oxygen, water, LiOH, battery) were all sized to run out around the same time (with margin) as there's no point in carrying the extra weight of, say, a lot more oxygen that you can't use anyway.

But if you wanted to extend the endurance of the PLSS by increasing all of the consumables, the one that would probably get you first would be the cooling water, simply because you need so much of it. The tanks took up a good fraction of the PLSS interior volume. After that probably comes lithium hydroxide, as it's also quite bulky.

The OPS carried quite a bit more O₂ than the main tank in the PLSS because it had to be sized for a once-through scuba-like mode in case the PLSS died.

Oxygen should be abundant in a future lunar base because it can easily be made from lunar soil; like the earth, it's about half oxygen by weight. So in principle you could do without LiOH and probably cooling water in a future EVA suit by simply squandering oxygen in an OPS-like once-through mode, assuming you can physically carry enough with you. This might actually be practical for surface treks with short EVAs from a pressurized rover. It could carry lots of O₂ as LOX.
 

[ka9q]

Like many of the discussions here, this got me thinking. Could abundant oxygen production on the moon allow the use of simpler but less efficient life support systems?

I see a range of numbers, but a typical human breathing air exhales 4-5% CO₂ and 15-16% O₂. Since air is about 21% O₂, this means that in a once-through scuba-type mode your oxygen efficiency would be about  25%. Assuming these figures would stay the same for pure O₂ at reduced total pressure (i.e., same O₂ partial pressure), you'd have to carry about 4x as much O₂ as in a conventional rebreather-type life support system where the CO₂, H₂O and trace gases are scrubbed so the unbreathed O₂ can be breathed again.

That's actually not bad considering how much you can get rid of: no CO₂ absorption system, no water condenser/separator, no charcoal filter. Depending on the workload you might also be able to get rid of the cooling system too by relying on gas cooling supplemented by the heat of vaporization of LOX. (Gas cooling was the original plan for Apollo, but water cooling was added when studies showed that at very high workloads it would take less power to drive a water pump than a suit blower at the necessary speed.)

But it would require you to use a scuba-type mouthpiece or a small face mask to limit mixing between exhaled and inhaled air. If instead you simply purged the cabin continuously through a vent, assuming good ventilation keeping exhaled air thoroughly mixed in the cabin, your vent rate would depend on the maximum tolerable CO₂ concentration. That appears to be about 1%, so to maintain that level you'd have to continuously vent CO₂ as fast as its produced, and you'd have to vent roughly 99 times as much O₂ along with it. (The actual figure is a bit better because CO₂ has a higher molecular weight than O₂.)

So if we take the oxygen efficiency of the conventional rebreather as 100%, the efficiency of a scuba system would be about 25% and that of a purged and vented cabin with ventilation would be about 1%. Still, if oxygen is truly plentiful -- and there's no reason to think that it wouldn't be on the moon -- this might be a worthwhile tradeoff to simplify the life support system, especially if it got rid of the need for other consumables that might not be as available. I know the ISS is now using a renewable CO₂ scrubber, and I know that compact cooling systems that don't expend water are under development, but it would be even better if you could simply do without them.