scrubbers? And draught excluders.

[aclivity]

I was reading about the Apollo programme recently, and it reminded me of a scene in Apollo 13 and an associated question about rebreathers.

The scrubber in an Inspiration is rated to last 3 hours. I've seen a couple of nude desperations, and the scrubber cartridge looks about the size of a 2l pop bottle.

In the Apollo program, the scrubbers were about the size of a biscuit tin, and lasted 3 guys over 150 hours.

Why isn't it possible for a rebreather scrubber to last so much longer?

(as you can tell, this isn't a serious query, but one just out of interest!).

The second part is slightly more whimsical:

It's the purpose of lots of building products (double glazing, draught excluders) to stop air exchange between the inside and outside of houses. IF it were possible to fully seal a family home, how long would it be before the air turned foul? In the same way, the climate control in my car has an option to 'recirculate' air rather than take it in from outside. There's no scrubber in my car (yes, yes, I know) so I assume the air in the car would turn foul too?

Sorry if these are silly questions, this is what you get when you spend 4 hours on the M25 every day - too much time for the mind to wander!

Andy

[Mark Chase]

Didnt the apolo chaps breath pure 02? I remember a vary nasty 02 fire that killed a couple of them. Knowing what I do now I have no idea how they did that they should have fried their lungs and toxed.

ATB

Mark Chase

[Brass Monkey]

I don’t know about the percentage of Oxy they were breathing but were their scrubbers not using Lithium Hydroxide. Whereas the scrubber material used in recreational diving is made up from a combination of calcium and sodium hydroxides. The lithium must be a far more efficient absorbent. I think this is the same stuff that’s used in submarines. No doubt someone will be able to give the complete break down and an in depth explanation of the chemical process.

Talking about space, I wonder what they use for rebreathers and what they use as scrubber when doing an EVA.



Dave.

[Fathoms Down]

Originally Posted by Brass Monkey

I don’t know about the percentage of Oxy they were breathing but were their scrubbers not using Lithium Hydroxide.

Yes, the scubbers in the US space vehicles have traditionally (and still are) lithium hydroxide. I'm not much of a chemist but I seem to remember lithum and water arn't a good mix.... perhaps thats one of the reasons (cost probably being the major factor) that its not used in 'breathers.

[Padowan]

I think Lithium Hydroxide is a recognised scrubber absorbent for use in the Cis-Lunar Mk5P rebreather, but I think that this model has some really cool features which mean you can NEVER flood the loop - I have heard stories, (I don't know how true), that you can shange the scrubber canister for a fresh one whilst still underwater as there is some sort of water impermeable membrane on the canister whisl lets gas through, but keeps water out - perhaps something like Gore-Tex?

Anyone know any more about this?

What about the regeneration of Sorb - if there a process that you can go through to make the Sorb good again - probably not something for the average diver, but perhaps something that is possible for them to perform on the fly, in space, with the kind of budget that have?

[Duncan Price]

Firstly, NASA used lithium hydroxide rather than sodalime. LiOH is much more efficient especially as they used radial rather than axial scrubbers (which are better anyway). Also with a diving scrubber you have inefficiencies due to the flow rate under pressure. A scrubber operating at 1 bar is more effient than on at 2 bar etc.

Secondly, the Apollo program did operate using pure O2 - the Apollo 1 launchpad fire that killed Gus Grissom et. al. was caused by a fire in a 1 bar pure O2 atmosphere. The space shuttle and Russian programs use air.

The Russians used a binary scrubber which releases one molecule of O2 for every molecule of CO2 absorbed. The scrubber is truely natsy stuff and catches fire when wet (Mir fire).

NASA now use a regenerative system scrubbing CO2 with an organic amine which can be heated under vacuum (plenty of that about) to remove CO2 and recyle. Mixed metal oxide scrubbers using silver and zinc are being investigated. Unfortunateyl these are not suitable for diving systems - sodalime is way cheaper.

Duncan

[Brass Monkey]

Nice one Duncan,
How do you know all this stuff? Can you clue us in to what they use for rebreathers on the EVA's.


Dave.

[Padowan]

I think the stuff that gives off O2 and absorbs CO2 is called Superoxide, and the Russians used a canister of that along with a Sodalime scrubber in some of their Oxygen rebreathers - the IDA71 is an example I think.

[NotDeadYet]

Originally Posted by Mark Chase

Didnt the apolo chaps breath pure 02? I remember a vary nasty 02 fire that killed a couple of them. Knowing what I do now I have no idea how they did that they should have fried their lungs and toxed.

They didn't tox because they were in a hypobaric atmosphere, i.e. less than 1bar pressure. Same as the reason that sat divers can stay under pressure for a month at a time. Gas is irrelevant, it's what pressure it is breathed at that is important. However where gas mix does become important is in fire risk and there are guidelines for minimising risk, and all sorts of weird and wonderful hyperbaric fire extinguishers (some even involve pig blood). In a sat spread its actually quite hard to start a fire, but in a therapeutic chamber quite easy. I'd imagine a low pressure O2 environment would still support combustion readily as opposed to a low ppO2 mixed gas atmosphere.

One thing that did become a concern in the early space program was eye irritation even at low O2 pp's. Also DCI was a major concern.

[Duncan Price]

Originally Posted by Brass Monkey

How do you know all this stuff?

I'm a scientist - its my job to know weird shit.

Originally Posted by Brass Monkey

Can you clue us in to what they use for rebreathers on the EVA's.

Lithium hydroxide - see http://www.hq.nasa.gov/office/pao/Hi...alsj/plss.html for the Apollo suit design.

Duncan

PS. Superoxide is KO2 whereas the Russians use a binary mixture of two chemicals. Get water in the loop and the stuff will come looking for you. There's a significant difference in RB design for use in the dry - e.g. space suits, mines rescue etc. as one to be used for diving. Oh and yes it was pure O2 but at a reduced pressure. Stuff will burn on 0.2 atm of pure O2 in more or less the same way as in air at 1 atm.