Re: A case for the eradication of unmanned Mars missions

Jeff Davis (
Fri, 10 Dec 1999 20:06:04 -0800

On Wed, 8 Dec 1999 21:31:24 -0800 (PST)
Eugene Leitl <> writes:

>it would be interesting to launch relatively large payloads (say, myself
>oxygenated fluorocarbon flooding the lungs while floating in saline plus
>support hardware -- pickled monkey)

I've been thinking about this method of supporting living tissue against the deforming and eventually injurious forces of high g loads--basically the idea of firing a person out of a cannon without killing them--but I've never run across a rigorous analysis or even a serious qualitative treatment of the subject.

The first edition of Bennett and Eliot's, The Physiology and Medicine of Diving and Compressed Air Work, presents the results of experiments conducted to determine the effects on various organisms ( goats and tadpoles among others) of exposure to elevated hydrostatic pressure. It's been a while since I read that stuff, but I seem to recall that irreversible damage results at pressures between 150 and 300 atmospheres. Launched in a supine position, immersed in say 9 inches deep (3/4 foot) of saline, the hydrostatic pressure would vary linearly from zero at the surface to a maximum at your back, where it would range from 150 to 300 atmospheres at accelerations ranging between 6,670 to 13,300 g's respectively. Because the duration of these g forces is likely to be very brief, I doubt that there would be much of a problem with injury due to elevated hydrostatic pressure. (Though I'd certainly want to confirm that with some experiments on hamsters, before trying it out personally! ;-) ).

Structural stresses is where the problem would seem to lie, and they arise from the differential between tissue density and the density of the supporting medium--saline in gene's post. Bone is, I believe, the most dense tissue, it should be the least buoyant, the least supported by the medium, but, of course, it is also quite strong structurally. Muscle would be the most dense after that, then watery non-muscle tissues, then fatty tissues. The differences between these tissues don't seem like they would be large enough, however, (ie, I'm guessing here) to make tearing due to differential buoyancy likely. That leaves the unsupported weight of bone bearing down on itself as the likely site of failure. (This might be reduced somewhat by making the supporting medium denser still, thus transferring a little of the stress to the bone-to-flesh attachment. In this situation the flesh tends to be buoyed up, lifting up on the bone and thereby relieving a certain amount of the stress.)

This is the best I can do on short notice. If you gene, or anyone knows "the facts" or has heard of a rigorous treatment of this issue, I'd love to hear about it. (I just know the military has worked on this--those psychos. Shortly after the successful immersion of mice in fluorocarbon, some demented darpa animal-torment specialist was no doubt popping them into 105mm artillery rounds, and yelling, "Fly Mickey, fly!" as he pulled the lanyard. The m112 stroke 4 mk I rodent round. Lovely.)

Best, Jeff Davis

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