More rebreather thoughts | Life Support Workgroup | Forum

Some more ideas with regards to using a standard rebreather for life support.  In case you can't tell, I'm very keen on this idea!  It seems to me to best implement our ideal of keeping things cheap and simple by using off-the-shelf hardware wherever we can.

What if we had the astronaut nominally breathing through a standard rebreather using a mouthpiece (or facemask, or whatever is easiest), but also had the cabin pressurised with a breathable atmosphere, so that the mouthpiece could be safely removed for periods to facilitate drinking, eating, vomiting, suiting up/down, etc.?  How many 15 minute stints of breathing the cabin atmosphere do you think could take place before either the oxygen levels in the cabin became dangerously low or the carbon dioxide levels became dangerously high?  Even if the answer to this is "less than we would realistically need", a simple solution, which does not involve a separate scrubbing system for cabin, would be to gently vent the cabin atmosphere into space until the pressure got as low as was safe (obviously the astronaut is using the rebreather mouthpiece during this process!), then close the venting valve and release some fresh atmosphere into the cabin until pressure is back up to nominal.  Possibly this process could be repeated 2 or 3 times each time the cabin atmosphere needs "refreshing".

This solution is slightly wasteful of the atmosphere gas, but probably (based on intuition) not so wasteful as to make it impractical, and it is certainly simple.  It combines the "we can just use an off-the-shelf rebreather!" simplicity of OpenLuna's "lock the astronaut in a suit" approach with the "I can drink and eat freely!" convenience of having an environmental control system for the entire cabin, without introducing much complexity at all.

The biggest danger would be taking off the rebreather mask if the oxygen levels in the cabin were low.  As I understand, you can't really tell that the oxygen level is dangerously low, you just sort of get pleasantly sleepy and then pass out.  So the oxygen level of the cabin would need to be monitored somehow (aside: does anybody know what process is used to determine the oxygen content of an atmosphere that is a mix of O2, N2 and CO2?), and clearly displayed on the instrumentation, with visibile and audible warnings for low levels.  Obviously a second rebreather to fall back on if the first should fail would be a necessity.

We could possibly even have the rebreather which is used during the flight be the same one that is used in the EVA suit's backpack.  The backpack would serve as the CM's life support system during most of the flight, connected to an external supply of consumables and power.

Thoughts?

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I'm not necessarily sure that this approach would really help us gain anything over filtering the entire cabin

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My thought was that it gains us the ability to just take an entirely off-the-shelf, tested and proven rebreathing aparatus from the diving or firefighting etc. industries and "tick the box" for this part of life support.  We don't need to design, build and test anything new of our own or modify what already works (and potentially break it).  I suppose, to be completely fair about it, we have to build the system for slowly venting the cabin and then refreshing it, but this is (unless I've missed something) just a couple of valves.  I think that desiging/building that sort of system would be significantly easier than building, e.g. our own scrubbing system.

Thanks for sharing your thoughts on this.  For what it's worth, I don't really know anything about this sort of technology, with regards to how complex things are, or what they cost.  My prime motivation is to make sure we don't reinvent wheels that already exist.  Diving rebreathers have been worked on and perfect for a long time now, so if there is anyway we can come up with to just use one of those off-the-shelf with little or no modifications, I think we should do it.

As a rule of thumb, very, very little has been thought out in any real depth, so if you find anything that you want to comment on, please feel very free.  Even if something has been thought out a lot, extra input never hurts.  You may point out something important which has been overlooked!