From: gee@dciem.dciem.dnd.ca (Thomas Gee)
Newsgroups: rec.aviation.military
Subject: Re: Aurora
Date: 23 Dec 92 23:04:32 GMT
Organization: Defence and Civil Institute of Environmental Medicine

In article <BzoHFs.95v@acsu.buffalo.edu> v111qheg@ubvmsb.cc.buffalo.edu (P.VASILION) writes:
>
>Q: What kind of ejection seat / survival system would be needed  to get the
>pilot down from mach 8+?
>
>A: One, the pilot must wear a an astronauts space suit to prevent his blood
>from evaporating and his skin from flaking off.

Nonsense.

Your blood does not boil at altitude, nor does your skin flake off (at
least, no more quickly than at sea level.)  Your blood does not boil
because it is under considerable pressure within your body (and that
pressure does not change markedly under decreased ambient levels).
Although some of the moisture in your skin must boil off, it doesn't take
your skin with it.  (I can attest to this through personal experience,
having been exposed to 72,000 feet altitude for a minute or so in an
almost shirt-sleeve environment.)  If you mean that your skin would flake
off because of windblast, well, perhaps.  I don't know.

[Begin long discourse about high-altitude "get me down" systems.]

The most immediate problem with high-altitude exposure is the fact
that an insufficient amount of oxygen is entering your blood (partial
pressure is below that required to sustain consciousness).  To solve that
problem, we inject the oxygen into your lungs at a pressure above ambient
(called positive pressure breathing, or PPB).  At 72,000', that pressure
is 80mmHg (little more than 1/10 of an atmosphere) above ambient.

Ok, the only problem here is that your lungs are now trying to leave
your body.  So, we put a really tight jerkin (or vest) on you, to keep
your ribcage more-or-less where it should be.

However, now we have another problem.  You can't breathe out.  Or, actually,
you might be able to breathe out a couple of times, but you will fatigue
quickly (ordinarily it doesn't take any muscular effort to breathe out, so
the intercostal muscles are very weak).

Well, we can solve that one.  We will put bladders in the jerkin, and tee
off from the mask to the bladders.  Now you have 80mmHg pressure in the
mask, and the same pressing on the outside of your chest, so you are
breathing almost normally again.

But now you have very high pressure throughout your chest wall, since there
is 80mmHg inside and out.  So all of your blood rushes down into your
legs (and abdomen) and you pass out and fall over.

Not good.

However, since we also do high-G work, we are already familiar with this
problem.  We put an anti-G suit on you (like a very tight pair of jeans
with bladders on the quads, calves, and abdomen) and inflate it, forcing
the blood back into your heart.

And there you are, feeling bloated like the Michelin Tire man, with a
blood pressure about 60-70 mmHg over your normal level, but conscious.
(Of course, this only works for about 4-5 minutes using standard USAF
gear, and after that you pass out and fall over again, but you only
need 2-3 minutes to get below 22,000' where you don't need PPB any longer.)

[End long discourse.]

>Two, no seat / spacesuit
>could survive the "windblast" at altitude and speed. Therefore, either the
>AF doesn't expect pilots to survive a break up at cruise and havn't put a 
>survival system in, or they would have to have an escape capsule, perhaps
>like the F-111 series or the B-58's and XB-70's personal ejection capsule.

This may fit in to what was being discussed wrt Mach numbers at various
altitudes, but at high altitude (say, 90,000') the air pressure is only
12.9 mmHg) (1/60th of an atmosphere), so would the windblast still be as
punishing as, say, 600 knots at sea level?  (Ok, naive question, I know.)

>What does everyone else think?

Thanks for asking.	:-)

Tom
---
Thomas Gee  -=-  S/W Development  -=-   gee@dretor.dciem.dnd.ca
Aerospace/Biosciences, DCIEM, CFB Toronto, DND, Canada
Disclaimer: the previous is solely the opinion of the author.