Space Forum / Space Flight / January 2006

Found it, Thanks

http://www.hq.nasa.gov/office/pao/History/afspbio/part5-4.htm

<begin quote>

As indicated by this last type of experimentation, the  Aeromedical Field
Laboratory is one of the various research agencies currently interested in
the use of fluids for g-protection. Journalists and information officers
have taken delight in tracing the theoretical principles involved in this
all the way back to ancient Greece, and In giving credit to Archimedes as
the spiritual father of underwater g-protection. The starting point for
modern research in this field appears to be a German effort in the 1930's
to develop water-lined anti-g suits. Even better known are Canadian tests
during World War II in which the subject was spun on a centrifuge with
most of the body under water. The Canadians were looking for ways to
improve their aircraft anti-g suits, and they decided at the time (as the
Germans had earlier) that water protection was not wholly practical for
this purpose.
     
Since 1957, the United States Navy's Aviation Medical Acceleration
Laboratory and the Aero Medical Laboratory at Wright Field have been
conducting human centrifuge tests on the water-immersion principle. So
far, the Navy holds the record as to maximum g-forces sustained with the
aid of water immersion: four seconds above fifteen g's, with a peak of
sixteen. This is part of one simulated re-entry pattern, and indications
are that "considerably" higher tolerance levels can be attained in future
experiments. But the Wright Field scientists, whose present equipment sets
a limit of about twelve g's for this type of testing, hold the record as
to durations. Tolerance has been established at twelve g's for almost four
minutes.

<end quote>

Peak for a human is 16 g's, with the upper limit unknown.

<quote>
 
Though dizzy from spinning at the end of the run, the mice survived
exposure to 400 g's for almost fifteen seconds.

<end quote>

If the acceleration had been linear, the mice would be on their way out of
the solar system. 400 g's sounds more like an impact, not something that
would want to be sustained for 15 seconds.

It's the density of the fluid that matters most, humans, more or less have
the same density as water. It really depends upon how much air is in your
lungs. Inhale, float, exhale, sink. I was actually thinking higher density
water (salt water) might be better, so that person would float at the
surface even when they exhale.

The amount of water required to float really depends on the container. It
can be quite small. The design of the seat is really an engineering
problem, where many other factors would come into play.

For space tourism, the number and complexity of these other factors is
reduced. As the tourist is just a passenger, human cargo. So, comfort and
safety become more important than maneuverability and control. Also, when
financial resources are factored in, the average age of the group of
potential customers for the  space tourist industry is quite high. Elderly
space tourist are more fragile and have more medical problems. The vehicle
with lower physical/medical constraints has a disproportionately larger
available customer pool and is more economically viable.

Water is very valuable in orbit, so it's mass isn't a constraint on
ascent, only on entry. True today, and even more so in the future when
there will be an onorbit  fuel depot at the space station. As well as the
swimming pool, which is really just a reservoir.

Returning sick or injured astronauts is another area were the value of the
mass of water coming down from orbit is unimportant. An astronaut/space
tourist that becomes ill at the space station can't be left up there.
Having a Zero Gee Entry Seat on hand for returning them to Earth in the
least stressful way would factor into the physical/medical constraints
placed on space tourists.

Another link:

http://www.hq.nasa.gov/office/pao/History/Timeline/1958.html

All quite true, but...

(it won't be water

Actually, water is a bit less dense than the human body.  The only
reason we float is that we have lungs and stomach that are filled with
air, which overcomes the body's tendency to sink, especially in fresh
water.

The real problem stems from these air-filled cavities -- in very high g
situations, the surrounding fluid pressure will crush the rib cage and
lungs.  This is discussed in, e. g.,

http://www.luf.org/wiki/view/TMP/BifrostBridge?rev=1.2.

The solution to that is the same as for all high-pressure environments:
fill the lungs with an oxygenated fluid.  As far as I've been able to
find, this is still a research project, even for high-pressure
environments, and is still little more than speculation for high-g
regimes.

I'm sure some of the more knowledgable can amplify and correct my
comments.

John Perry

Found it, Thanks

http://www.hq.nasa.gov/office/pao/History/afspbio/part5-4.htm

<begin quote>

As indicated by this last type of experimentation, the  Aeromedical Field
Laboratory is one of the various research agencies currently interested in
the use of fluids for g-protection. Journalists and information officers
have taken delight in tracing the theoretical principles involved in this
all the way back to ancient Greece, and In giving credit to Archimedes as
the spiritual father of underwater g-protection. The starting point for
modern research in this field appears to be a German effort in the 1930's
to develop water-lined anti-g suits. Even better known are Canadian tests
during World War II in which the subject was spun on a centrifuge with
most of the body under water. The Canadians were looking for ways to
improve their aircraft anti-g suits, and they decided at the time (as the
Germans had earlier) that water protection was not wholly practical for
this purpose.
     
Since 1957, the United States Navy's Aviation Medical Acceleration
Laboratory and the Aero Medical Laboratory at Wright Field have been
conducting human centrifuge tests on the water-immersion principle. So
far, the Navy holds the record as to maximum g-forces sustained with the
aid of water immersion: four seconds above fifteen g's, with a peak of
sixteen. This is part of one simulated re-entry pattern, and indications
are that "considerably" higher tolerance levels can be attained in future
experiments. But the Wright Field scientists, whose present equipment sets
a limit of about twelve g's for this type of testing, hold the record as
to durations. Tolerance has been established at twelve g's for almost four
minutes.

<end quote>

Peak for a human is 16 g's, with the upper limit unknown.

<quote>
 
Though dizzy from spinning at the end of the run, the mice survived
exposure to 400 g's for almost fifteen seconds.

<end quote>

If the acceleration had been linear, the mice would be on their way out of
the solar system. 400 g's sounds more like an impact, not something that
would want to be sustained for 15 seconds.

It's the density of the fluid that matters most, humans, more or less have
the same density as water. It really depends upon how much air is in your
lungs. Inhale, float, exhale, sink. I was actually thinking higher density
water (salt water) might be better, so that person would float at the
surface even when they exhale.

The amount of water required to float really depends on the container. It
can be quite small. The design of the seat is really an engineering
problem, where many other factors would come into play.

For space tourism, the number and complexity of these other factors is
reduced. As the tourist is just a passenger, human cargo. So, comfort and
safety become more important than maneuverability and control. Also, when
financial resources are factored in, the average age of the group of
potential customers for the  space tourist industry is quite high. Elderly
space tourist are more fragile and have more medical problems. The vehicle
with lower physical/medical constraints has a disproportionately larger
available customer pool and is more economically viable.

Water is very valuable in orbit, so it's mass isn't a constraint on
ascent, only on entry. True today, and even more so in the future when
there will be an onorbit  fuel depot at the space station. As well as the
swimming pool, which is really just a reservoir.

Returning sick or injured astronauts is another area were the value of the
mass of water coming down from orbit is unimportant. An astronaut/space
tourist that becomes ill at the space station can't be left up there.
Having a Zero Gee Entry Seat on hand for returning them to Earth in the
least stressful way would factor into the physical/medical constraints
placed on space tourists.

Another link:

http://www.hq.nasa.gov/office/pao/History/Timeline/1958.html