What is wrong with Artificial Gravity spacecraft ??
Richard Frost
Why is NASA spending millions of dollars researching the long-term effects
of micro-gravity on the human body?
After seeing 2010 years ago it became apparent to me that the design
of the russian spacecraft used for the long journey to Jupiter avoided the
problems involved with the chronic exposure to micro-gravity environments.
It did this by rotating a separate section of the ship quickly enough
to re-create earth type gravity.
This question was talked about on sci.space last year but I cannot
remember what the outcome of the discussion was, I think that this should
be considered more seriously, as just swinging a counterweight on a
tether gives you very cheap gravity for a long journey.
As we all know, artificial gravity avoids all the problems (bone
decalcination, muscle deterioration, blood cell deformities, etc.)
inherent with long zero-g missions, ie. the Mars mission.
I know that one of the Gemini missions did this (at very low angular velocity)
with an Athena (?) capsule.
WHY has NASA dropped this line of ship design?
I have discussed this with some friends of mine that suggested why this
approach may not work.
1) The structure when rotating may produce certain resonances that
cannot be damped in a zero-g environment.
2) The Gemini Mission resulted in the tether oscillating in length.
3) Due to rotations of the ship, there would be torques produced that
would effect navigation of the ship.
Are any of these above problems serious ? (I don't think so.)
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Henry Spencer
>Why is NASA spending millions of dollars researching the long-term effects
>of micro-gravity on the human body?
>to re-create earth type gravity.
The problem with artifical gravity by spin is the physiological effects
of rotation. Centrifugal force is not a good substitute for gravity
when spacecraft are small. If you ever have a chance to ride a centrifuge,
*do not* turn your head at high G -- you will tumble your gyros but good.
(I started to try it -- very cautiously and slowly, as I'd heard it was a
bad idea -- in the space-simulation ride at the Marshall visitor's center,
and hastily recentered my head and aborted the experiment. :-)) Things
like coriolis effect have fairly serious effects on the human balance system,
and the spin rate needs to be slow enough to keep this under control.
Orthodox wisdom is that spin rate should not exceed 1 RPM. For a 1G field,
this means a spin radius of 890m, which is an awfully large spacecraft,
even if it's two lumps linked by a minimal truss. (Linking them with a
flexible tether reduces mass but adds serious control problems.) There
is work underway on whether somewhat higher spin rates would be tolerable,
and also on innovative ways of dodging the problem, but overall, artificial
gravity is not as easy as it looks. Spaceship design would be much simpler
if it wasn't necessary. (It would also make the astronauts happier -- they
*like* free fall and would prefer to avoid artificial gravity.)
--
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Mark Earnshaw
>The problem with artifical gravity by spin is the physiological effects
>of rotation. Centrifugal force is not a good substitute for gravity
>when spacecraft are small. If you ever have a chance to ride a centrifuge,
>*do not* turn your head at high G -- you will tumble your gyros but good.
>(I started to try it -- very cautiously and slowly, as I'd heard it was a
>bad idea -- in the space-simulation ride at the Marshall visitor's center,
>and hastily recentered my head and aborted the experiment. :-)) Things
>like coriolis effect have fairly serious effects on the human balance system,
>and the spin rate needs to be slow enough to keep this under control.
The following is an experiment that anyone can do at home and which illustrates
the effects of rotation on the inner ear (thereby affecting your sense of
balance). I had it done to me many years ago at the Science Centre in
Columbus, Ohio.
Sit in a swivel chair and put your head sideways onto your shoulder. Have
someone spin you around (it doesn't have to be really fast) for a minute or
two. It might be best to keep your eyes shut at this point. When the other
person stops the chair from rotating, open your eyes and straighten your head
up. It feels like you're falling forward out of the chair.
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Mark Earnshaw, Systems Design Engineering {uunet,utai}!watmath!watnow!mark
University of Waterloo, Ontario, Canada ma...@watnow.waterloo.{edu,cdn}
Donald Lindsay
>this means a spin radius of 890m, which is an awfully large spacecraft,
>even if it's two lumps linked by a minimal truss. (Linking them with a
>flexible tether reduces mass but adds serious control problems.) There
>is work underway on whether somewhat higher spin rates would be tolerable,
>and also on innovative ways of dodging the problem, but overall, artificial
>gravity is not as easy as it looks. Spaceship design would be much simpler
>if it wasn't necessary. (It would also make the astronauts happier -- they
>*like* free fall and would prefer to avoid artificial gravity.)
So, why use 1 G? Wouldn't Martian or Lunar gravity levels be a better
standard?
One sixth of 1 G, at 1 RPM, would be a lot easier to do. Naively,
that's about 150m of truss: but actually, it should be even less,
since some of the truss was there to support itself.
As for the wins - it would make it a lot easier to set up food/air
production, and I recall the Apollo astronauts complaining about the
problems of 0-G construction work.
Plus, health. The fact that some long-term cosmonauts weren't as
affected as others tells me that some _were_ affected badly. Do we
really want explorers arriving at Mars in that kind of shape? And in
the longer term, we hope to have a lot of people in space: I don't
see that making the health issue any easier. There was a report
recently about depressed immune responses: is there any way to tell
if it's due to confinement rather than zero gee?
It would be interesting to find out if working at zero, and sleeping
at lunar (or vice versa) made a significant difference.
--
Don D.C.Lindsay
Robert Casey
>this means a spin radius of 890m, which is an awfully large spacecraft,
Do they know if they really need 1G in the spacecraft, or maybe they could get
by with less, like 1/6 G? That would make the spin problems easier to deal
with if the astronauts can live in fractional G environments.
lawrence.m.geary
>this means a spin radius of 890m, which is an awfully large spacecraft,
Although we have results of the effects of 0g on humans, we have no
results of the effects of low-g on humans. It could well be that something
less than 1g, say 1/5g, would be sufficient to arrest the deterioration
experienced by astronauts. If it isn't, we can't live on the moon (1/6g)
or probably Mars (1/3g) long term anyway, so the efforts to set up
permanent bases in these places would not be a good idea. We can still,
though, send Mark S. to Venus. :-)
I think the original poster's point is a good one. 0g is a known dead end,
and we should be investigating simulated gravity via rotation. We need to
determine whether there is a livable g level < 1 and > 0. I do not think
that high-g investigations in high rpm/small radius centrifuges on the
ground should be considered the last word on the subject. This is something
that can only be researched in space.
--
Larry Geary: 74017...@compuserve.com | Kuwait: Caught between
l...@mtqub.att.com | Iraq and a hard place
Henry Spencer
>>Orthodox wisdom is that spin rate should not exceed 1 RPM. For a 1G field,
>So, why use 1 G? Wouldn't Martian or Lunar gravity levels be a better
>standard?
It would certainly be an *easier* standard. But our knowledge of the
biological effects of low gravity is negligible. In-space research would
be needed, and nobody is doing it yet. 0.95G is almost certainly an
adequate substitute for 1G, and 0.05G very probably isn't, but there
is a vast gray area in between.
>Plus, health. The fact that some long-term cosmonauts weren't as
>affected as others tells me that some _were_ affected badly...
You have to look at the time sequence as well, though: the situation
has been improving, so there definitely *are* things that can be done
about it. The question, still somewhat open, is whether they are enough.
>... depressed immune responses: is there any way to tell
>if it's due to confinement rather than zero gee?
Obviously, one can test confinement on Earth, although there are some
inevitable differences...
>It would be interesting to find out if working at zero, and sleeping
>at lunar (or vice versa) made a significant difference.
Quite so. There are some people with devious schemes for applying
artificial gravity during sleep. Again, the proof of the pudding
is probably going to have to be in-space tests.