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From: SOTOS@sumex-aim.arpa (John Sotos)
Newsgroups: sci.space
Subject: The vestibular system in rotating structures
Message-ID: <12251039742.21.SOTOS@SUMEX-AIM.ARPA>
Date: Thu, 30-Oct-86 19:11:14 EST
Article-I.D.: SUMEX-AI.12251039742.21.SOTOS
Posted: Thu Oct 30 19:11:14 1986
Date-Received: Fri, 31-Oct-86 03:30:45 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 61

There has been some discussion about rotating space colonies lately,
mostly concerned with the reliability of bearings.  My recollection
was that the idea of rotating structures to produce pseudogravity was
out because of problems with Coriolis forces and the human vestibular
system.  I have not seen this point made in print, the only time I
heard it mentioned was at the 1977 Princeton Conference by somebody
from NASA-Ames.

The theoretical anatomic/physical basis for the problem is given later
in this note; evidence to justify concern that the problem really will
happen comes from experiments made at the Navy's Pensacola Research
Center in the 1960s.  These guys built a room on a motorized lazy
susan (known as "the rotating room") and put subjects in there to live
for some amount of time.  Basically, people with intact vestibular
systems got motion sick because every time they turned their head,
effects of Coriolis forces in their inner ear produced the illusion
that they were rotating in a completely different plane.  (You can do
this at home!  Twirl around as fast as you can for 30-40 seconds with
your eyes/head looking straight ahead.  Then quickly look down at the
floor and you will feel like your feet are trying to swing above your
head.  Do this 15 or 20 times and you might find it disagreeable.)

I have forgottent the details of their research (those interested can
check the Archives of Neurology in the mid-60s for articles by Ashton
Graybiel), but I seem to recall that adaptation either did not occur
or was only partial, and that even very slow rpm (on the order of 3)
was enough to produce symptoms.  So, if you allow a maximum rpm of 3
and try to produce earth gravity in your space colony, you have to
have a structure with a very large radius (it's an easy calculation,
if you remember how to do it!).  Clearly, pseudo-gravity will not be
possible for a Mars trip in a reasonably sized spacecraft.  The
physiological benefit of less than earth gravity over extended times
has, of course, not been investigated.

(The Coriolis problem stems from the anatomy of the vestibular system.
Each ear has three orthogonal "semicircular canals" (that are
functionally closer to being circular) filled with fluid.  The
movement of the fluid in each canal tells the brain whether the head
is rotating in the same plane that the semicircular canal occupies.
If rotation in a plane is prolonged, the fluid in the corresponding
canal equilibrates (that is, the fluid and the canal bone eventually
will rotate at the same speed).  This is the basis for the phenomenon
that if you spin in a chair long enough, you no longer feel like you
are moving.  So in a slow-rotating-room or a space station, the fluid
in the canal that is in the same plane as the room's rotation is
equilibrated.  But moving your head cancels all bets: a new canal is
now in the plane of rotation of the room, and the still-moving fluid
in the old canal is now in a plane that was formerly stationary.  Your
brain integrates all this and tells you what it thinks; sadly, your
other balance senses (vision, proprioception) tell you otherwise,
and you have a sensory conflict that soon results in nausea.  Of
interest is that Guinea pigs may be immune from this problem.  Their
canals are nowhere near orthogonal (presumably since their ancestors
were not arboreal and didn't need high performance balance systems),
so the cross-coupling forces would be much smaller.  I guess it proves
that man was not to fly after all!)

				John Sotos
				Stanford University
				SOTOS@SUMEX-AIM.STANFORD.ARPA
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