Re: How long will a given supply of air last?

Thanks for all the answers everyone.

Quoting Hop, Nov 5, 1:14 am :
>FWIW, there are 3-4 semi-independent components of air recycling.
>Oxygen production, CO2 removal, trace contaminant removal, and
>condensate removal. They may or may not be tied together.

I knew it wouldn't be simple=-) Good job the only space stations I have
to design are imaginary ones.
I never realised that o2 generation and CO2 removal were seperate
processes. I assumed the CO2 scrubbers extracted the oxygen and dumped
it back into the atmosphere, killing two birds with one stone. Instead
they just store the CO2 in some form and then dump it into space/ ship
it back to Earth/ feed it to the plants, do they?


>Also, if you are going for realism, one would expect such a station to have backup systems.

This is a very good point, but a somewhat inconvenient one. I can break
the backups easily enough, I guess (the malfunction in my story is not
accidental).



Now quoting Matti Anttila Nov 5, 12:31 pm :
> 1) The increasing percentage of CO2 does matter. At some point, when the
> amoun of CO2 is high enough, the poor astronaut begins to feel dizzy, and
> looses his/her consciousness. This happens significantly before that the
> O2 reserves (from surrounding air) has depleted.

Quote from Cray74@xxxxxxxxx Nov 5, 4:01 pm :
> However, without carbon dioxide scrubbers, I think the limiting factor
> will be CO2 build-up, not oxygen depletion. Normal 8-hour exposure
> limits are 5000ppm (0.5%). When carbon dioxide levels reach 10%, you
> can quickly (~10 minutes) pass out and die.
...
> might say CO2 levels become a problem in half the time that oxygen
> depletion would be a problem.

This is valuable information to me. The whole story hinges around CO2
anyway, so this is the angle I will approach from: I will break the CO2
removal systems. Thanks.
I understand CO2 poisoning is quite unpleasant: Pain in the muscles
from lactic acid buildup and so on. Is that right?


> As a WAG,

Wildly Accurate Guess?


Quoting Cray74@xxxxxxxxx Nov 5, 4:01 pm :
>Note that unless your station is small, a lot of the air may prove hard
>to access. Sure, there's fresh air in the all the cubic meters of
>maintenance tunnels, but are your protagonists going to run around
>looking for fresh air pockets?

Actually, yes. I'd very much like my station to be in the classic
"doughnut" shape (spinning for apparent gravity- think Blue Danube bit
from 2001), with my two characters involved in a long, pointless
pursuit around and around and around...
I realise that this introduces problems of its own (ie, if you build it
too small and spin it, you induce nausea) but the shape is important.


> I mean, they're so simple
> that it'd almost be reasonable to stick some [oxygen candles] in every corridor or
> module of a station as back-up systems.

Yeah, this is another very sensible point, but potentially somewhat
troublesome. Do these oxygen candles burn like flares, or is the
reaction more slow and controlled? What is the chemical reaction
involved? Presumably, having oxygen locked up in an easily-released
form like that, it might be possible to engineer some kind of explosive
or torch-weapon from an oxygen candle. Having one character attack the
other with a weapon fashioned from their only source of survival might
add a nice touch of extra irony to their unfortunate situation.


Quoting Frank Scrooby Nov 7, 6:13 am :
> If your protoganists have the time / equipment / motivation / energy /
> sufficiently large heat sink all they need to do is routinely cool some part
> of the atmosphere to ?78 °C. The CO2 will sublimate out as dry ice. Then
> all you have do is sweep it up and put it somewhere air tight and safe where
> it can't contaiminate the rest of the air supply.

Wow, I had no idea this kind of thing might be possible. Sadly, my
protagonists are seem to be too busy chasing one another to death to
work together for mutual survival.

I'll go back through this thread and re-approach my problem from a
broken CO2-scrubber perspective. This is good, since it would appear
that this problem (as opposed to o2 availability) would require a much
larger starting volume of fresh air to provide my planned 2 days, and a
larger starting volume means I can probably design a reasonable-sized
doughnut station. However, I can probably stretch things out to give
them an extra day or two,

Thanks again everyone. When I have the story written, I'll be sure to a
post a link to it in this thread.


.

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