Date: 25 Jun 87 20:20:07 GMT
From: jtk@mordor.s1.gov  (Jordan Kare)
Subject: Re: High G and playing with life

In article <12313116013.39.SOTOS@SUMEX-AIM.STANFORD.EDU> SOTOS@SUMEX-AIM.STANFORD.EDU (John Sotos) writes:

>There are several points to be made about high G forces, blackouts,
>neurological damage, and so forth.
...
>The issue of "posture" is not a detail, it is critically important.
>People blackout from G-forces when the acceleration is in the +Gz
>direction (ie, blood is drawn out of the head toward the feet).
>Pilots of high performance aircraft can usually tolerate about +9 Gz
>with use of G-suits, straining maneuvers, etc....
>
>Acceleration from front to back (+Gx) can be tolerated to a much
>higher degree.  Ham the chimp took +17 Gx during the launch of his
>Mercury-Redstone flight and -14 Gx during re-entry.  (The description
>in The Right Stuff is a joy!)  Apollo re-entries gave the astronauts
>-7 Gx ("eyeballs out") or so.

There is also a strong time dependence.  I have in front of me a 
plot from Webb, Paul M. D. "Bioastronautics Data Book,", NASA SP-3006, 1964
titled "G Tolerance in 4 vectors".  It is unfortunately not clear if
"tolerance" means before blackout, or before some other limit; also, it
is not clear if this includes the use of G-suits, etc.  Since the
plot is included in a design study for a high-acceleration vehicle, I
think it is safe to assume these are roughly what NASA considers safe for
manned vehicles:

Time (min)	+Gx	-Gx	+Gz	-Gz
.01 (<1 sec)	35	28	18	8
.03 (2 sec)	28	22	14	7
.1		20	17	11	5
.3		15	12	9	4.5
1		11	9	7	3.3
3		9	8	6	2.5
10		6	5	4.5	2
30		4.5	4	3.5	1.8

All the curves are straight lines on log-log paper with slopes of around
1/4.  Note that the -Gz curve goes below 1 at something like 200 minutes --
this is therefore the maximum time that NASA recommends for standing
on your head :-) :-).

There is also a plot on "Acceleration Onset Tolerances" (from USAAVLABS
Tech Rept. 67-22, "Crash Survival Design Guide") which indicates that
up to 30 G's of acceleration, the rate of change of acceleration should be
limited to 600 G/sec.  At 1370 G/sec, the plot indicates "Definite signs of
shock", and at 3400 G/sec, "Cardiovascular Shock -- heart function and
blood circulation have stopped".


>I would be willing to be blacked out by acceleration stress, but only
>for a second or two.  Brain cells do not appreciate being without
>oxygen for very much longer than that.
>
>	John Sotos
>	Stanford U.

Seems to me the limit for beginning of organic damage is more like 3-4 
minutes, but I wouldn't volunteer to test that....

	Jordin Kare

Date: 1 Aug 91 17:58:46 GMT
From: ssc-vax!bcsaic!hsvaic!eder@beaver.cs.washington.edu  (Dani Eder)
Subject: Re: Over 1 g endurance

In article <3343@ptolemy.ACA.MCC.COM> rsb@ptolemy.ACA.MCC.COM (Richard S.
Brice) writes:

>Is anyone aware of experimental results which confirm that the human body
>will continue to function well under g-loades greater than 1-g for very
>long periods of time? (I've seen at least one work of science fiction 
>which suggests otherwise).


A quotation from "Great Mambo Chicken & the Transhuman Experience" by
Ed Regis (Addison Wesley, 1990):

[pp 54-55]
. . . For that matter, humans could also have survived at even HIGHER
levels (italics in original are uppercase here), as has been demonstrated
repeatedly by experimental tests.

     There was the hyper-G work done on chickens, for example, by
Arthur Hamilton ("Milt") Smith in the 1970s.  Milt Smith was a gravity
specialist at the University of California at Davis who wanted to find
out what would happen to humans if they lived in greater-than-normal
G-forces.  Naturally, he experimented on animals, and he decided that
the animal that most closely resembled man for this specific purpose
was the chicken.  Chickens, after all, had a posture similar to man's:
they walked upright on two legs, they had two non-load-bearing limbs
(the wings), and so on.  Anyway, Milt Smith and his assistants took a 
flock of chickens -- hundreds of them, in fact -- and put them into
the two eighteen-foot-long centrifuges in the university's Chronic
Acceleration Research Laboratory, as the place was called.

     They spun those chickens up to two-and-a-half Gs and let them
stay there for a good while.  In fact, they left them spinning like
that day and night, for three to six months or more at a time.  The
hens went around and around, they clucked and they cackled and they
laid their eggs, and as far as those chickens were concerned that was
what ordinary life was like: a steady pull of two-and-a-half Gs.  Some
of those chickens spent the larger portion of their lifetimes in that
goddamn accelerator.

     Well, it was easy to predict what would happen.  Their bones
would get stronger and their muscles would get bigger--because they
had all that extra gravity to work against.  A total of twenty-three
generations of hens was spun around like this and the same thing
happened every time.  When the accelerator was turned off, out walked
. . .GREAT MAMBO CHICKEN!

     These chronically accelerated fowl were paragons of brute
strength and endurance.  They'd lost excess body fat, their hearts
were pumping out greater-than-normal volumes of blood, and their
extensor muscles were bigger than ever.  In consequence of all this,
the high-G chickens had developed a three-fold increase in their
ability to do work, as measured by wingbeating exercises and
treadmill tests
[end quote]

References:

Smith, A. H. "Physiological Changes Associated with Long-Term
     Increases in Acceleration." In "Life Sciences and Space
     Research XIV", edited by P.H.A. Sneath. Berlin:Akademie-Verlag, 1976.
Smith, A. H., and C. F. Kelly. "Biological Effects of Chronic
     Acceleration." NAVAL RESEARCH REVIEWS 18 (1965): 1.
_____. "Influence of Chronic Acceleration upon Growth and Body
     Composition" ANNALS OF THE NEW YORK ACADEMY OF SCIENCES 110
     (1963): 410.



-- 
Dani Eder/Boeing/Advanced Civil Space/(205)464-2697(w)/461-7801(h)/#905, 1075
Dockside Dr.,Huntsville,AL35824/Member: Space Studies Institute
Physical Location: 34deg 37' N 86deg 43' W +100m alt.
***THE ABOVE IS NOT THE OPINION OF THE BOEING COMPANY OR ITS MANAGEMENT.***

Newsgroups: sci.space.shuttle
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: Re: Challenger crew
Date: Sun, 16 Feb 1997 16:46:25 GMT

In article <33055813.1717504@nntp.ix.netcom.com>,
Michael R. Grabois <orbit@ix.netcom.com> wrote:
>>>I remember reading that they were cut up into pieces  when they hit the water
>>>- that they went "through" their safety harnesses (seat belts).
>>Unlikely -- the human body is much tougher than typical seat structures.
>>Usually the seat breaks loose from its mountings before any major damage
>>is done to the body.
>
>The chairs and attach points in the shuttle are rated for 20 G's. The human
>body generally isn't.

You need to do a bit more research on the subject.  There is a very large
difference between continuous acceleration and very brief acceleration,
i.e. impacts, when it comes to human survival.  A 20G impact is not even
particularly severe; parachute-opening shocks reach that level.  John
Stapp survived 50G rocket-sled braking, with some injuries.  My old copy
of NASA's "Bioastronautics Databook" says that the limit of survival for
impacts is circa 175-200G, with a footnote that any single number is
misleading because it depends on many factors.
--
Committees do harm merely by existing.             |       Henry Spencer
                           -- Freeman Dyson        |   henry@zoo.toronto.edu

From: henry@spsystems.net (Henry Spencer)
Newsgroups: sci.space.science,sci.space.shuttle
Subject: Re: maximum G
Date: Wed, 8 Jul 1998 16:50:55 GMT

In article <6nmois$6s3$2@news-int.gatech.edu>,
Arislan <joseph@resnet.gatech.edu> wrote:
>this might have been asked before but that is the maximum G a person
>can take?

Depends on duration, rate of onset, extent of training, etc.  A quick rule
of thumb (from a graph in my old Bioastronautics Data Book) is that the
average healthy person, taking the acceleration flat on his back, can
handle 20G for a few seconds, 10G for a minute, and 5G for many minutes.
(Remember that people vary, so you will need to add some safety margin if
you want an acceleration that *most* healthy people can handle.)  Training,
practice, and motivation improve the short-term tolerances somewhat.
--
Being the last man on the Moon is a |  Henry Spencer   henry@spsystems.net
very dubious honor. -- Gene Cernan  |      (aka henry@zoo.toronto.edu)

From: jamesoberg@aol.com (JamesOberg)
Newsgroups: sci.space.shuttle
Subject: Re: maximum G
Date: 13 Jul 1998 15:40:25 GMT

For sustainable G's, there were minutes-long centrifuge runs up to 16-18, I
think -- there was physical damage. Soyuz-18-A in april 1975 (abort landing
into Mongolia)  took about 18+ G's for 30 seconds or so and the cosmonauts
suffered massive blood vessel rupture across their bottom sides (Cernan saw one
of the guys in the gym shower at Star City afterwards, said his back looked
like a "roadmap" of red and blue lines, including even the incised labels and
creases of his underwear).

BUT it has been suggested to FLOAT bodies in fluidized beds to have bouyancy
offset acceleration. That would help the body-to-seat interface but the
internal stresses would still be damaging.

Stapp's short-time high-G acceleration was equivalent to that experienced by
football players running into each other, and by boxers running into gloves .
50+ G's even for very short intervals causes cerebral bleeding and loss of
function -- even Stapp, people who knew him well privately related, couldn't do
his crossword puzzles as well, after his sled runs.