Reduced Gravity: the 400-kilogram gorilla in the room

[Esme]

(10-20-2015, 07:22 AM)JoeStrout Wrote: Well, you should read the Globus & Hall paper.  It includes a lot of research from the 80s, which of course nobody would have known about in 1978. But please do share your thoughts on it!

And I'll see if I can get either of those guys to jump into the discussion here.

That's excellent, thank you! The main thing that would concern me about the data from those studies is that the test subjects all appear to be members of the armed forces, who will, of course, tend to be fitter than average. Given we're talking about space settlement, then ultimately we're talking about the infirm and very old and young as well, who may be affected differently. And thinking about it, I'd expect short people to suffer less negative effects than tall ones (because the apparent gravity gradient from head to foot would be lower, plus their heads would be that bit further from the axis of rotation)

It'll certainly be interesting to see what happens when some actual in-orbit research into this is done!

[JoeStrout]

Yes, absolutely we need to find out both (1) how much rotation can ordinary people tolerate (and how long does it take them to adapt), and (2) how much gravity is enough.

I suspect we'll start getting these answers once we start having orbital hotels. The toilet issue will push hotel developers to start rotating, very soon after we've cleared out the market of die-hard would-be astronauts willing to use the zero-G plumbing.

[JoeStrout]

I wrote to Ted Hall about this thread, and while he may jump in later, he's a bit swamped this week.  But he dashed off a quick reply, and said he wouldn't mind if I quoted him on it.  So, here we go:

Quote:My counter-argument, in brief:  The 1 RPM limit seems to be based on the

assumption that people can't adapt, or that any period of adaptation is
unacceptable.  However, we make no such demand on microgravity.  It has
been observed over decades, and accepted without hesitation, that about
half of all astronauts / cosmonauts are afflicted with "space adaptation
syndrome" that lasts from 1 to 3 days.  A similar period of adaptation
to artificial gravity seems perfectly reasonable to me, especially for
exploration or early settlement habitats.  Studies show that most people
can adapt to 3 RPM within a day or two, and most published comfort
charts for AG put the upper limit at 4 or even 6 RPM.

Years ago, in a USENET discussion group, I encountered a person who
seemed very knowledgeable about many things -- especially physics -- who
wrote confidently that anything above 1 RPM would make people violently
ill.  The available published research absolutely refutes that, and I
called him on it, citing all of the published research to the contrary.
I think he might have been confusing 1 RPM with 1 radian/second, which
equates to about 10 RPM and is another matter entirely.

Thanks, Ted!

My own thoughts:

Of course tourism may be another matter, because tourists are there for only a relatively short time, and don't want to spend it feeling ill.

On the other hand, motion sickness is pretty common on cruise ships, but that hasn't hurt the cruise industry.  Also, many passengers avoid it by using drugs (Dramamine, Meclazine, etc.).  These drugs are also commonly used for passengers on the Zero-G flight to help avoid "space sickness" (motion sickness) there, too.  As far as I know, all the rotation tolerance studies were done in the absence of any motion-sickness drugs.  So it's quite possible that tourists would be just fine at 4-6 RPM as long as they slap on a patch before launch.

[Esme]

I take your points gentlemen, but I'd also add that it hasn't yet been demonstrated that a full 1G is necessary for good health and comfortable living. I speak only for myself, of course, but I wouldn't be inclined to regard an environment that induces motion sickness as being a pleasant place to visit, let alone live in - and I'd also add that I am one that avoided all fairground rides (aside from bumping cars/dodgems) after discovering that even the mildest of such tend to make me violenty ill causing effects that lasted for hours afterwards. So yes, there is bias behind my skepticism, but that said, I believe data - it's a shame we haven't yet got more of it on this subject. Here's hoping we don't have to wait too many more years before some is obtained!

Hmmn..I've just had a thought; in an early and small toroidal station, one could have a number of habitable spokes extending outwards from the torus, to give a limited volume at a higher G than the bulk of the torus, if the simulated gravity in the torus itself was deemed to be a tad low for long term health. It'd be a bit like having buildings sunk into the ground ( rather like, IIRC, Jinx in Larry Niven's Known Space series of tales), with the top floor at ground level. Might that be easier to build than a larger torus?- And if that were practicable, maybe at a later date a second outer ring could be built linking what was teh basement of each spoke?

[JoeStrout]

(10-30-2015, 01:27 PM)Esme Wrote: Hmmn..I've just had a thought; in an early and small toroidal station, one could have a number of habitable spokes extending outwards from the torus, to give a limited volume at a higher G than the bulk of the torus, if the simulated gravity in the torus itself was deemed to be a tad low for long term health. It'd be a bit like having buildings sunk into the ground ( rather like, IIRC, Jinx in Larry Niven's Known Space series of tales), with the top floor at ground level. Might that be easier to build than a larger torus?- And if that were practicable, maybe at a later date a second outer ring could be built linking what was teh basement of each spoke?

Sounds like a reasonable plan to me!

[TWHall]

(10-18-2015, 02:03 PM)JoeStrout Wrote: @antred, I'm not too worried about that... that's one activity that humans are very good at (and often quite creative).

@Esme, you have a point: all the rotating-room research so far has been done on Earth, where you have a 1G field at an angle to whatever pseudogravity you're adding on top.  So it's hard to be sure how those results will generalize to the real situation where you're spinning in microgravity.  But the results are encouraging, anyway!

Much of the work on rotation tolerance has been done on upright subjects in rotating rooms, with the spine perpendicular to the centripetal force.  That does confound the application of the findings to orbital environments detached from Earth.  We absolutely do need to follow up with more and larger space-based experiments.

However, back in the 1960s, NASA Langley Research Center had a rotating space station simulator with an elaborate suspended harness system to support the subject in the appropriate orientation -- spine parallel to the centripetal force.  It was 40 feet in diameter and could rotate up to 10.5 rpm.  Unfortunately, it was dismantled following the NASA agency-wide reduction in force of 1971.

A nice historic video is on YouTube here:  https://www.youtube.com/watch?v=2EHwT33YCAw

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(10-30-2015, 01:27 PM)Esme Wrote: I take your points gentlemen, but I'd also add that it hasn't yet been demonstrated that a full 1G is necessary for good health and comfortable living. I speak only for myself, of course, but I wouldn't be inclined to regard an environment that induces motion sickness as being a pleasant place to visit, let alone live in - and I'd also add that I am one that avoided all fairground rides (aside from bumping cars/dodgems) after discovering that even the mildest of such tend to make me violenty ill causing effects that lasted for hours afterwards. So yes, there is bias behind my skepticism, but that said, I believe data - it's a shame we haven't yet got more of it on this subject.  Here's hoping we don't have to wait too many more years before some is obtained!

The problem is that it hasn't yet been demonstrated that a full 1g is not necessary for good health.  We don't know whether the physiological benefits of gravity scale linearly with dose (intensity integrated over time), or whether there's a threshold.  Until we have more data on that, 1g is the safe bet.

About half of all astronauts and cosmonauts endure 1 to 3 days of "space adaptation syndrome" before they're comfortable in microgravity.  I don't know whether the space tourism companies communicate that to their prospective "guests."  The pop media never mention it.  Interestingly, susceptibility to motion sickness on Earth or in aerodynamic flight doesn't seem to correlate with susceptibility to space sickness; it's not a predictor, one way or the other.

When we talk about settlements, we should also consider that even here on Earth pre-industrial cultures have flourished for centuries in conditions that outsiders find difficult to adapt to -- for example: high altitudes in the Himalayas and Andes; cold in the high Arctic; heat and dryness in deserts.

I think we have to let go of the image of space settlements as Utopian perfections of American suburbia.  Space is a frontier that will be settled by frontier people.  Free-space rotating settlements will comprise living situations unlike anything ever encountered before, and the settlers must and will adapt.  Attentive, proactive design can (hopefully) assist that.  Ultimately these settlements must be designed by people who have been there.

Apologies for the rambling tangent ...