SOTOS@sumex-aim.arpa (John Sotos) (10/31/86)
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 -------
news@cit-vax.Caltech.Edu (Usenet netnews) (10/31/86)
Organization : California Institute of Technology Keywords: From: jon@oddhack.Caltech.Edu (Jon Leech) Path: oddhack!jon In article <12251039742.21.SOTOS@SUMEX-AIM.ARPA> SOTOS@sumex-aim.arpa (John Sotos) writes: >... 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. We can obtain arbitrarily large radii by connecting two modules with a cable. It should be straightforward to see if a combination of 1g and low enough RPMs can be obtained with reasonable materials (Kevlar cable, perhaps?). I hate to think of the cable breaking, though... -- Jon Leech (jon@csvax.caltech.edu || ...seismo!cit-vax!jon) Caltech Computer Science Graphics Group __@/
henry@utzoo.UUCP (Henry Spencer) (10/31/86)
> 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... If you check out Gerry O'Neill's original book "The High Frontier" (1978?), you will see it in print. The problem has been known since quite early in the history of the space-colony concept. This is why O'Neill's definitive large-colony designs spin at 1 RPM or less. This does make for troublingly large structures; he suggested that a small first colony, with crew selected for resistance to such problems, might be able to spin at 2-3 RPM. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,decvax,pyramid}!utzoo!henry