Re: Mission of Gravity, China Lake style

Jeff Davis (jdavis@socketscience.com)
Sun, 12 Dec 1999 21:41:50 -0800

"Lucky, lucky, lucky, lucky,lucky,..." 

                             Sigorney Weaver as "Riply" in "Alien"

Regarding centrifuging guppies and other critters IN A LIQUID MEDIUM to see how they tolerate g-loads

On Sat, 11 Dec 1999 07:19:04 -0800
"Michael M. Butler" <butler@comp-lib.org> writes:

<Hey-what-happens-to-this-grasshopper-if-I-put-it-in-my-Estes-payloader story elided>

<TEN MINUTES?!? Whoa, Nellie!!>

Which seems to suggest that ten minutes at 100 gees is some serious exposure. Perhaps. But let's have some context.

In spike's original experiment, he writes that he

>bought a dozen guppies, put em in a plastic thermos bottle,
>put the bottle in the centrifuge and spun em up to 100 g for 10
>minutes.

Now if the thermos bottle is upright at the bottom of the centrifuge, and if the liquid level is nine inches, then the hydrostatic pressure at the very bottom is (100 gees x .75 ft) the equivalent of a water depth of 75 ft. (If the two meter centrifuge had a two meter water column, the median gees for the column would be 50, and the pressure at the very bottom the equivalent of approx 350 ft of water.) Now guppies don't normally live at these depths, but all in all I would guess the stresses of such exposure--the hydrostatic stresses, that is-- to be utterly trivial. Whether for ten minutes or ten years. (After a while, they did stop swimming in spirals, didn't they, spike? )

So, as I mentioned previously, I'm looking at mechanical stresses on the skeleton as the likely limiting factor/mode of failure.

A serious test would be to spin them up, and determine the locus of points--plotted as duration vs gee load (depth of the supporting liquid medium kept constant and at a minimum)--where they suffered some irreversible effect/injury . I wouldn't be surpised if it happened--for fish--around 5-10,000 gees.

The situation for humans is complicated by the problem of gas filled spaces in the interior of the body--lungs, sinuses, middle ear, semicircular canals of the inner ear, and bowel gases. Fill the lungs, sinuses and middle ear with fluid, and you probably wouldn't have a problem up to oh, say, a thousand gees. If the blastronaut were lying on a molded support, to evenly support the downward pressure of the bones, the only part of the skeleton not supported would be the anterior portion of the rib cage, and the bones of the middle ear.

So, tentative conclusion, no big deal. Meanwhile, ten minutes at a mere 100 gees gives you 1,309,150 mph terminal velocity. One second at 1000 gees gives you 21,800 mph. Whoa, Nellie, indeed!

Best, Jeff Davis 

	   "Everything's hard till you know how to do it."
					Ray Charles