Space station future adrift (Soyuz purchase crisis)

(Henry Spencer) writes:

In article ,
Derek Lyons wrote:
It's also possible to design an emergency escape suit *that doesn't
require prebreathing*. Get in it, seal it, and pop out the airlock.
Prebreathe while dropping the pressure down to a level where you can
move the suit, complete the remainder of the escape sequence.

Unfortunately, starting from the station's normal 14.7psi atmosphere, suit
prebreathing even on an emergency basis takes about four hours, which is
kind of a long time to just float in the suit. (Preplanned spacewalks use
less prebreathing time than that because those guys live in reduced
pressure, with increased oxygen content, for 12+ hours first.)


My references indicate that the Russians use a thirty-minute prebreath from
one standard atmosphere to Orlan suit pressure. Admittedly, the Orlan is a
higher-pressure suit than NASA's designs, and the Russians are willing to
risk higher R values, but it would seem that in an evacuate-the-station
class emergency even NASA ought to be able to stretch the margins enough
to allow a similar half-hour prebreath.

Which still leaves you with that first half an hour to deal with, and my
references may have overlooked an oxygen-rich pre-prebreath such as you
allude to, but I'm skeptical of the four-hour figure as a hard limit for
emergency operations.


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h (Rand Simberg) writes:

On 6 Dec 2004 21:00:27 -0800, in a place far, far away,
(John Schilling) made the phosphor on my
monitor glow in such a way as to indicate that:

And Pottinger may be right; at low pressure the biological effects
are probably not linear with bends ratio and it probably is possible
to get by with less prebreathing than current protocols require.
How much so is unknown, and until we do the research we have little
choice but conservative extrapolation from bends data derived from
high-pressure diving experience.

I remain skeptical that we have enough data/experience to confidently
extrapolate hyperbaric situations to hypobaric ones.

Perhaps, but we certainly don't have enough data to directly quantify
the hypobaric situations, so extrapolation is what we got.


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*Member:AIAA,NRA,ACLU,SAS,LP * is worth doing for money" *
*Chief Scientist & General Partner * -13th Rule of Acquisition *
*White Elephant Research, LLC * "There is no substitute *
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John Schilling wrote:
(Henry Spencer) writes:
Derek Lyons wrote:
It's also possible to design an emergency escape suit *that doesn't
require prebreathing*. Get in it, seal it, and pop out the airlock.
Prebreathe while dropping the pressure down to a level where you can
move the suit, complete the remainder of the escape sequence.

Unfortunately, starting from the station's normal 14.7psi atmosphere, suit
prebreathing even on an emergency basis takes about four hours, which is
kind of a long time to just float in the suit. (Preplanned spacewalks use
less prebreathing time than that because those guys live in reduced
pressure, with increased oxygen content, for 12+ hours first.)


My references indicate that the Russians use a thirty-minute prebreath from
one standard atmosphere to Orlan suit pressure. Admittedly, the Orlan is a
higher-pressure suit than NASA's designs, and the Russians are willing to
risk higher R values, but it would seem that in an evacuate-the-station
class emergency even NASA ought to be able to stretch the margins enough
to allow a similar half-hour prebreath.

Which still leaves you with that first half an hour to deal with, and my
references may have overlooked an oxygen-rich pre-prebreath such as you
allude to, but I'm skeptical of the four-hour figure as a hard limit for
emergency operations.

If you pass 1.6 by very much you get bent. There seems to be good
hypobaric evidence for that.

One of the things which is not well mapped right now is what level of
bent is acceptable for emergencies. The bends are not an immedately
fatal or incapacitating incident. Bubbles take time to form under most
circumstances, and you can still function, in moderate to extreme pain,
if you have a moderate case of the bends. Or so I have heard; I have
not had the pleasure myself.

Normal operations have to be designed to avoid it as much as possible,
because no matter how much you can tough through it, it is going to
be a risk and risk permanent damage if it happens to you. Emergency
ops and procedures can tolerate trading risks off, on a one time basis.


-george william herbert

George William Herbert wrote:
One of the things which is not well mapped right now is what level of
bent is acceptable for emergencies. The bends are not an immedately
fatal or incapacitating incident.

Unless bubbles form in your brain.

However, the NAVY has experience with the bends. For instance, during aircraft
wreckage recovery, the divers are pulled up from the bottom very quickly
without any decompression stops and they have a fixed set of minutes to get
out of the diving suit and go into hyperbaric chamber for a while where a
proper decompresison is done. Bubbles that had already formed get redisolved
when the chamber is pressurized.

Consider a bottle of 7UP. As soon as you remove the lid, bubbles form. But
obviously, nitrogen disolved in your fat/skin/muscles takes longer to escape
from those tissues. Blood is more dangerous, however blood also has a much
quicker way to get rid of its excess nitrogen: the lungs (when you exhale).

John Schilling wrote:

h (Rand Simberg) writes:

[...]

I remain skeptical that we have enough data/experience to confidently
extrapolate hyperbaric situations to hypobaric ones.

Perhaps, but we certainly don't have enough data to directly quantify
the hypobaric situations, so extrapolation is what we got.



What devices do have for measuring N2 saturation and/or bubble formation?
Could a retinal observation give us useful measurements? If so, can the
measuring device be small enough to take into Quest or the shuttle
mid-deck, so that the EVA crew can be measured at various points during
the prebreathe?

FWIW, the following tool (see
http://www.sciencedaily.com/releases/2004/12/041203101104.htm and
http://www.umich.edu/news/index.html?Releases/2004/Nov04/r112904c) isn't
directly applicable, but the optical portion of it might relate somewhat.

quote
Astronaut's Eyes May Become Windows On The Bloodstream

ANN ARBOR, Mich. -- Our eyes may become more than windows of the soul if a
multidisciplinary team of University of Michigan researchers succeeds with
a clever combination of nanoparticles and ultrafast pulsed laser to see
individual cells as they zip past in the bloodstream.

The U-M team of physicians, scientists and engineers has $3 million from
NASA to determine a way of detecting radiation exposure on the fly by
looking for individual cells that have been harmed. Now, such cell
counting is only achieved by drawing blood and using an expensive machine
called a cytometer, operated by a skilled lab technician.

A certain amount of cell death is normal and expected, so there would
always be some background fluorescence. What the researchers are looking
for is a sudden increase in the population of dead white blood cells,
which is one of the calling cards of radiation poisoning.
[...]
/quote

/dps

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Greg D. Moore (Strider) wrote:


"Henry Spencer" wrote in message
[...]
But at donning time, you're still trying to put on something that's
squeezing hard all the time. What's needed is a way to turn that off
and on, either on command or automatically in response to ambient
pressure (a fabric that shrinks in vacuum). Not simple.


No, something simpler. Something that reacts to a piezoelectric force.

Done a nice loose fitting suit, plug in the battery, bamm... skin tight.


Piezoelectric probably won't do it, for various reasons (mainly amount of
movement; piezo's are very good a t samll movements). EAP might. See the
SciAm article on plastics being developed for muscle use:

From the October 2003 issue ,
quote
Artificial Muscles
Novel motion-producing devices--actuators, motors, generators--based on
polymers that change shape when stimulated electrically are nearing
commercialization
By Steven Ashley

It's only a $100 toy--an aquarium of swimming robotic fish developed by
the Eamex Corporation in Osaka, Japan. What makes it remarkable is that
the brightly colored plastic fish propelling themselves through the water
in a fair imitation of life do not contain mechanical parts: no motors, no
drive shafts, no gears, not even a battery. Instead the fish swim because
their plastic innards flex back and forth, seemingly of their own
volition. They are the first commercial products based on a new generation
of improved electroactive polymers (EAPs), plastics that move in response
to electricity.
/quote

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