Space station future adrift (Soyuz purchase crisis)

"Henry Spencer" wrote in message
...

With a normal elastic material, if you want to stretch it
twice as far, you have to apply about twice as much
force. But there are some materials, Spandex being one
of them if I recall correctly, which are different. They
start out the normal way, but when you reach a particular
amount of stretch, the curve flattens out: the material
stretches, and stretches more, and stretches still more,
with only the most minute increase of force. Eventually
the required force starts rising again, but there's a wide
flat section in the middle of the curve. This is exactly
what's wanted for a skinsuit: essentially constant force
over a wide range of stretch. Not only does this
accommodate flexing of the body, but if that range is
wide enough, it can also accommodate some discrepancy
between the design size and the actual size of the body.

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.

A possible approach that might get over some of these problems, but not
all, would be a double skin suit with both skins sealed together into
little squares perhaps a few millimeters to a side. Like a lilo but on
a much smaller scale. By pressurizing between the two skins you can
cause the suit to shrink down to 2/pi in any direction, and regulate
body pressure.

This could be sufficient for getting the suit on, and because the
inflated thickness is very small, (and can be partially balanced),
movement should be little impeded. Obviously this still tries to make
every part of the body circular, not dealing well with body corners,
flats, or hollows. Perhaps hybrid solutions might be possible.

Pete.

In article ,
Pete Lynn wrote:
...Obviously this still tries to make
every part of the body circular, not dealing well with body corners,
flats, or hollows...

Although this is a real issue with skinsuit concepts, the extent of it is
exaggerated. Hollows, and to some extent flats, are dealt with by putting
shaped air-filled balloons inside the suit. (In particular, you want a
substantial flat balloon, connected to the air system, on the chest so
that you can inhale without fighting several psi of pressure or needing
very tricky air-system controls.) A fabric with the non-linear stretch
characteristics I mentioned helps with corners and such, and careful
tailoring plus the non-linearity can at least reduce the circularization
problem.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Joann Evans 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

http://www.ardice.com/Games/Video_Ga...ystems/ADRIFT/

In article ,
George William Herbert wrote:
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.

As of about ten years ago (and probably still today), NASA's operating
rule was 1.4, which included a conscious decision to accept some chance of
mild symptoms. (Spacewalk crews take aspirin beforehand.)

There are other variables which seem to affect the results but haven't
been well studied:

+ Oddly enough, the probability of overt symptoms is rather lower when
you're in a spacesuit than when you're in shirtsleeves. Perhaps the
reduced mobility makes bubble formation in the joints less likely?

+ There are some hints that people who start from a low initial air pressure
are more susceptible than people from sea level, which is a concern for
proposals to use a lower cabin pressure.

+ Physical fitness is desirable -- body fat is a nitrogen reservoir -- but
intense levels of physical activity seem to make you more susceptible,
perhaps because minor tissue damage encourages bubble formation.

+ Women seem to be more vulnerable than men, and it seems to vary with
their menstrual cycle for some reason.

One big poorly-known variable is how honest the reporting of symptoms is,
especially when symptoms would affect the subject's career. It's clear
that a *lot* of low-level symptoms go unreported.
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

"Henry Spencer" wrote in message
...
Although this is a real issue with skinsuit concepts, the extent of it is
exaggerated. Hollows, and to some extent flats, are dealt with by putting
shaped air-filled balloons inside the suit. (In particular, you want a
substantial flat balloon, connected to the air system, on the chest so
that you can inhale without fighting several psi of pressure or needing
very tricky air-system controls.)

Is it possible to mix skin & traditional suit components? For example, use
"skinsuits" just for the forearms and hands and traditional suit components
for everything else. That would seem simpler than the above though the seam
between the traditional and skin suit parts might be tricky.

A more extreme version would be some type of "paint-on" glove that protects
the skin from exposure to vacuum but does not provide any significant
presure. Would the (slightly reinforced) skin have enough strength to
prevent your hands from swelling to the point that they could not be used?

In article ,
David Pugh wrote:
Although this is a real issue with skinsuit concepts, the extent of it is
exaggerated. Hollows, and to some extent flats, are dealt with by putting
shaped air-filled balloons inside the suit...

Is it possible to mix skin & traditional suit components? For example, use
"skinsuits" just for the forearms and hands and traditional suit components
for everything else.

Yes, there has been some work on giving the traditional suits skinsuit
gloves, since the gloves are the big disaster area in existing suits. The
idea does appear to be viable... provided you stick to low-pressure suits.

A more extreme version would be some type of "paint-on" glove that protects
the skin from exposure to vacuum but does not provide any significant
presure. Would the (slightly reinforced) skin have enough strength to
prevent your hands from swelling to the point that they could not be used?

Unfortunately, almost certainly not.

There actually isn't any real requirement to protect the skin from vacuum
exposure *apart* from the need for pressure. Indeed, that's one of the
basic ideas behind the skinsuit: that your skin is quite adequate as an
interface to vacuum, given mechanical support to supply pressurization.
In particular, a skinsuit's cooling system is that you sweat into vacuum.
(Typically there would be overgarments providing some overall temperature
control, and protection against hot/cold surfaces, but they wouldn't be
pressure-tight, indeed they'd be vented.)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(George William Herbert) writes:

Joann Evans 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.


More precisely, as I understand it, above 1.6 is not safe, period,
but extensive prebreathing reduces the bends ratio by reducing
blood ppN2.

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.


--
*John Schilling * "Anything worth doing, *
*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 *
* for success" *
*661-718-0955 or 661-275-6795 * -58th Rule of Acquisition *

"Rand Simberg" wrote in message
.. .

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

Especially when complaints about "minor" problems with the bends could have
an adverse effect on one's astronaut career. At the very least, such
complaints could severely limit the opportunities for future EVAs,
especially if other astronauts don't complain about the very same aches and
pains.

Jeff
--
Remove icky phrase from email address to get a valid address.

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.