Re: Space station future adrift (Soyuz purchase crisis)

From: George William Herbert (gherbert_at_retro.com)
Date: 12/06/04 

Date: 06 Dec 2004 06:20:14 GMT

Joann Evans <greenie31@juno[spambait].com> wrote:
>Earl Colby Pottinger wrote:
>>
>> Why does prebreath take so long? Bubbles? But at the lower pressure tere is
>> not that much gas in the blood, is there? People often dive to 30 to 50 feet
>> and come back up in time measured in minutes not hours. So why so long? And
>> if caution is the main reason for such a long time how much can it be cut
>> back for an emergency?
>
> The length of time one stays at a given depth, determines how long
>decompression time* will be....up to a point. Then one's tissues are
>saturated, and decompression time doesn't get any longer, no matter how
>much longer one stays at that pressure.

One thing that I don't recall seeing mentioned in the discussion
this time around is the bends ratio. This is the ratio of ppN2
to Pfinal.

A ratio of 1.0 or less is safe.

A ratio of 1.3 or less is safe for well conditioned people who
are selected for bends resistance (people's susceptability varies
widely among populations). The risks increase as the ratio climbs
from 1.4 to 1.6. Above 1.6 is probably not safe without very
extensive prebreathing.

One thing which would seem to have huge potential benefits for
spacefaring humankind would be looking at alternate atmosphere
mixes or running at moderately lowered habitat pressures.

There has been on and off research, but not with the sort of
vigor and support required.

There is some diving related research on various options;
they use nitrogen, helium, and oxygen mixes, and a few
mixtures using neon. Argon, which is a good choice for
spacecraft, isn't considered for diving because it becomes
a narcotic under higher pressure than sea level.

There have been extended research runs with helium-oxygen
before, deep dives and deep research stations. But those
were at high pressure. Looking at sea level and moderately
lower pressure effects (say down to 10 PSI, but most likely
12 PSI) would be valuable.

There are a few studies on normoxic argon mixtures at
sea level, which seem to indicate that it's safe for
moderate periods of time. I suspect that mixtures with
nitrogen and other gases will be better choices than
simple argon-oxygen mixes, but simplicity in the life
support system may push towards argon-oxygen two gas
systems. Dr Andrew Pilmanis among others has been
doing research on argon-oxygen mixtures for space
habitat usage. So far, the argon isn't proving a
magic bullet but it appears a lot better than
nitrogen is.

-george william herbert
gherbert@retro.com

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