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artificial gravity a different idea...maybe?



 
 
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  #21  
Old August 22nd 03, 04:25 AM
Christopher M. Jones
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Default artificial gravity a different idea...maybe?

"Jochem Huhmann" wrote:
"Christopher M. Jones" writes:
We don't know. All we know is that they don't happen at 1 g
and they do happen in micro-g. What happens in the range in
between is just speculation.


As far as I know this is not a direct consequence of zero-g (or micro-g)
but a consequence of missing that load on bones and muscles our body is
evolutionary optimized for. One could imagine that a person living in
micro-g but doing really hard work with frequent heavy loads on bones
and muscles would do quite well. And the other way round, people in 1g
just laying in bed for months *do* suffer loss of bone and muscle
density quite similar to those in zero-g.


Yes, it is all about the absence of load on bones and muscles,
and that causes atrophy in both. The real problem is that
excercise does not seem to be able to completely counteract
these effects. Astronauts who have been in orbit for the
better part of a year or longer than a year usually spend a
lot of time excercising (many hours per day). I don't know
all the specifics but I believe that while excercise does
help, even exercising a lot nearly every waking hour does not
completely counteract the effects.

Also, I believe that the bone and muscle loss in zero-g is
quite a bit faster than for bed ridden individuals.

Compared to zero-g, ordinary movement in 1 g is like
continuous, low impact excercise. Every time you lift your
arm up you're using your muscles and bones to lift the
weight of your arm against gravity, and that's a lot more
excercise than pushing around the mass of your arm in zero-g.

  #23  
Old August 22nd 03, 07:33 AM
Theodore W. Hall
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Default artificial gravity a different idea...maybe?

"Gordon D. Pusch" wrote:

... the "cylindrical surface" needs to be
about a =MILE= in diameter to get the rotation rate down below 1 rpm @ 1 gee,
since if it rotates faster than 1 rpm, the majority of human beings tested
upchuck. (Even at 1rpm, a significant fraction of the people tested upchuck;
you need to get the rotation rate down to about 0.25 rpm in order for the
general population to not upchuck.)



Umm, no, it's not =THAT= bad. Many studies put the upper range of "comfort"
at 3 or 4 rpm. Some put it as high as 6 rpm.

The most useful summary I've found -- one of the few that discusses
"comfort" as something other than an on/off switch -- is from Ashton
Graybiel, based on extensive research in ground-based centrifuges and
rotating rooms:

"In brief, at 1.0 rpm even highly susceptible subjects were symptom-free,
or nearly so. At 3.0 rpm subjects experienced symptoms but were not
significantly handicapped. At 5.4 rpm, only subjects with low
susceptibility performed well and by the second day were almost free from
symptoms. At 10 rpm, however, adaptation presented a challenging but
interesting problem. Even pilots without a history of air sickness did
not fully adapt in a period of twelve days.

Graybiel, Ashton (1977). "Some Physiological Effects of Alternation Between
Zero Gravity and One Gravity." _Space Manufacturing Facilities (Space
Colonies): Proceedings of the Princeton / AIAA / NASA Conference,
May 7-9, 1975_, pages 137-149. Edited by Jerry Grey. American Institute
of Aeronautics and Astronautics.

--

Ted Hall
  #24  
Old August 22nd 03, 05:02 PM
Gordon D. Pusch
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Default artificial gravity a different idea...maybe?

Christopher James Huff writes:

In article ,
(Gordon D. Pusch) wrote:

Possibly the little detail that the "cylindrical surface" needs to be
about a =MILE= in diameter to get the rotation rate down below 1 rpm
@ 1 gee, since if it rotates faster than 1 rpm, the majority of human
beings tested upchuck. (Even at 1rpm, a significant fraction of the
people tested upchuck; you need to get the rotation rate down to about
0.25 rpm in order for the general population to not upchuck.)


893 meters radius for full 9.8m/s^2 acceleration at 1rpm, unless my
calculations are off.


Note use of the word "about" in front of "diameter." 1786 meters only
differs by 11% from 1609 meters (~1 mile).


But the "radius" just has to be distance from center of rotation,
you don't need a complete cylinder. Two habitats at the ends of a
2km tether rotating at 0.6rpm would have 8m/s^2.


Granted. However, the point I was attempting to make to the poster was that
his naive notion that you could just spin the ship around an axis as in
old SF novels or have a small diameter "centrifuge" section as in _2001_
does =NOT= work, unless someone makes a =REALLY= major advance in treating
motion sickness.


And we haven't really tested its effects on humans...we haven't had
structures in which we *could* test it. Being close to the center will be
more disorienting, and more likely to cause nausea,


Why? Given a fixed rotation rate, the coriolis forces that case the
disorientation are independent of radius, so one should get just as
nauseous at the center of a 10 RPM space station as at its rim!


And people may get used to rotations exceeding 1rpm.


I would not care to bet my lunch on that hypothesis...


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

  #25  
Old August 23rd 03, 03:01 AM
Zoltan Szakaly
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Default artificial gravity a different idea...maybe?

(Gordon D. Pusch) wrote in message ...
Christopher James Huff writes:

In article ,
(Gordon D. Pusch) wrote:

Possibly the little detail that the "cylindrical surface" needs to be
about a =MILE= in diameter to get the rotation rate down below 1 rpm
@ 1 gee, since if it rotates faster than 1 rpm, the majority of human
beings tested upchuck. (Even at 1rpm, a significant fraction of the
people tested upchuck; you need to get the rotation rate down to about
0.25 rpm in order for the general population to not upchuck.)


893 meters radius for full 9.8m/s^2 acceleration at 1rpm, unless my
calculations are off.


Note use of the word "about" in front of "diameter." 1786 meters only
differs by 11% from 1609 meters (~1 mile).


But the "radius" just has to be distance from center of rotation,
you don't need a complete cylinder. Two habitats at the ends of a
2km tether rotating at 0.6rpm would have 8m/s^2.


Granted. However, the point I was attempting to make to the poster was that
his naive notion that you could just spin the ship around an axis as in
old SF novels or have a small diameter "centrifuge" section as in _2001_
does =NOT= work, unless someone makes a =REALLY= major advance in treating
motion sickness.


And we haven't really tested its effects on humans...we haven't had
structures in which we *could* test it. Being close to the center will be
more disorienting, and more likely to cause nausea,


Why? Given a fixed rotation rate, the coriolis forces that case the
disorientation are independent of radius, so one should get just as
nauseous at the center of a 10 RPM space station as at its rim!


And people may get used to rotations exceeding 1rpm.


I would not care to bet my lunch on that hypothesis...


-- Gordon D. Pusch


I remember riding a gravitron once. This is a ride in an amusement
park that people go into and after it starts spinning everybody is
stuck to the inside surface standing facing the center. In a little
while the floor drops out from under you and you are just stuck to the
wall. I don't remember anybody vomiting.

Zoltan
  #26  
Old August 23rd 03, 04:50 AM
Gordon D. Pusch
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Default artificial gravity a different idea...maybe?

"Theodore W. Hall" writes:

"Gordon D. Pusch" wrote:

... the "cylindrical surface" needs to be about a =MILE= in diameter
to get the rotation rate down below 1 rpm @ 1 gee, since if it rotates
faster than 1 rpm, the majority of human beings tested upchuck. (Even at
1rpm, a significant fraction of the people tested upchuck; you need to
get the rotation rate down to about 0.25 rpm in order for the general
population to not upchuck.)


Umm, no, it's not =THAT= bad. Many studies put the upper range of "comfort"
at 3 or 4 rpm. Some put it as high as 6 rpm.


Even a 50 meter radius is =NOT= what one would call a "small" cylindrical section!


-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'
  #27  
Old August 23rd 03, 07:32 AM
Marc 182
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Default artificial gravity a different idea...maybe?

In article ,
says...
(Gordon D. Pusch) wrote in message ...
Christopher James Huff writes:

In article ,
(Gordon D. Pusch) wrote:

Possibly the little detail that the "cylindrical surface" needs to be
about a =MILE= in diameter to get the rotation rate down below 1 rpm
@ 1 gee, since if it rotates faster than 1 rpm, the majority of human
beings tested upchuck. (Even at 1rpm, a significant fraction of the
people tested upchuck; you need to get the rotation rate down to about
0.25 rpm in order for the general population to not upchuck.)

893 meters radius for full 9.8m/s^2 acceleration at 1rpm, unless my
calculations are off.


Note use of the word "about" in front of "diameter." 1786 meters only
differs by 11% from 1609 meters (~1 mile).


But the "radius" just has to be distance from center of rotation,
you don't need a complete cylinder. Two habitats at the ends of a
2km tether rotating at 0.6rpm would have 8m/s^2.


Granted. However, the point I was attempting to make to the poster was that
his naive notion that you could just spin the ship around an axis as in
old SF novels or have a small diameter "centrifuge" section as in _2001_
does =NOT= work, unless someone makes a =REALLY= major advance in treating
motion sickness.


And we haven't really tested its effects on humans...we haven't had
structures in which we *could* test it. Being close to the center will be
more disorienting, and more likely to cause nausea,


Why? Given a fixed rotation rate, the coriolis forces that case the
disorientation are independent of radius, so one should get just as
nauseous at the center of a 10 RPM space station as at its rim!


Hum, nearer the center the coriolis force may be the same, but the G's
are less. It may be that the difference between the two is an important
factor. At the very center you'd be simply rotating slowly in 0g. You
could stand that indefinitely. Disorientation could be less as you move
to the center. This kind of thing needs testing, it's hard to predict.

And people may get used to rotations exceeding 1rpm.


I would not care to bet my lunch on that hypothesis...


-- Gordon D. Pusch


I remember riding a gravitron once. This is a ride in an amusement
park that people go into and after it starts spinning everybody is


You didn't lift your head from the wall and look around. I did once,
disorientation and nausea was instant. Pretty profound actually.

Marc
  #28  
Old August 24th 03, 05:19 AM
Joann Evans
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Default artificial gravity a different idea...maybe?

Zoltan Szakaly wrote:

[snip]

I remember riding a gravitron once. This is a ride in an amusement
park that people go into and after it starts spinning everybody is
stuck to the inside surface standing facing the center. In a little
while the floor drops out from under you and you are just stuck to the
wall. I don't remember anybody vomiting.

Zoltan


I've been on a similar ride (floor doesn't drop, but once spun up,
the whole thing is tilted up to about 45 degrees), but similarly, the
forces were perpendicular to my body. Now if the same size ring were in
free fall, and I tried walking 'upright' on it, I might not have enjoyed
it as much.

Now also throw in windows that would give uncomfortable visual
references to a 'spinning' Earth below....

  #29  
Old August 25th 03, 05:58 AM
Theodore W. Hall
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Default artificial gravity a different idea...maybe?

"Gordon D. Pusch" wrote:

Given a fixed rotation rate, the coriolis forces that case the
disorientation are independent of radius, so one should get just as
nauseous at the center of a 10 RPM space station as at its rim!


Yes, the nausea is mostly a consequence of rotation -- specifically:
rotating one's head about an axis that's not aligned with the
station's rotation.

However, the ratio of Coriolis to centripetal acceleration is also an
important design consideration. One would like to keep that ratio
low. With a fixed radius, you can reduce that ratio by increasing
the rotation rate, but then you come up against the nausea issue.
There are trade-offs ...


Christopher James Huff writes:

And people may get used to rotations exceeding 1rpm.


I would not care to bet my lunch on that hypothesis...


Sorry, Gordon, but you're off by about an order of magnitude.
1 radian per second (9.55 rpm) is indeed too fast, but 1 rpm is not.

Estimates of the upper limit of angular velocity for "comfortable"
rotation:

Hill & Schnitzer (1962) 4 rpm
Gilruth (1969) 6 rpm
"optimum" 2 rpm
Gordon & Gervais (1969) 6 rpm
Stone (1973) 6 rpm
Graybiel (1977) 3 rpm *
Cramer (1985) 3 rpm

* "subjects experienced symptoms but were not significantly
handicapped."

Keep in mind that 50% of all astronauts / cosmonauts need 1 to 3 days
to adapt their vestibular systems to microgravity. An equal adaptation
period for artificial gravity would not be unreasonable, especially for
a small exploration-class vehicle, appropriate for the first trips to
Mars.

* * *

Hill, Paul R.; Schnitzer, Emanuel (1962). "Rotating Manned Space
Stations." _Astronautics_, vol. 7, no. 9, p. 14-18, September 1962.
American Rocket Society.

Gilruth, Robert R. (1969). "Manned Space Stations - Gateway to our
Future in Space." _Manned Laboratories in Space_, p. 1-10. Edited
by S. Fred Singer. Springer-Verlag.

Gordon, Theodore J.; Gervais, Robert L. (1969). "Critical Engineering
Problems of Space Stations." _Manned Laboratories in Space_,
p. 11-32. Edited by S. Fred Singer. Springer-Verlag.

Stone, Ralph W. (1973). "An Overview of Artificial Gravity." _Fifth
Symposium on the Role of the Vestibular Organs in Space Exploration_
(NASA SP 115), p. 23-33. NASA Scientific and Technical Information
Division. Proceedings of a symposium held in 1970.

Graybiel, Ashton (1977). "Some Physiological Effects of Alternation
Between Zero Gravity and One Gravity." _Space Manufacturing
Facilities (Space Colonies): Proceedings of the Princeton / AIAA /
NASA Conference, May 7-9, 1975_, p. 137-149. Edited by Jerry Grey.
American Institute of Aeronautics and Astronautics.

Cramer, D. Bryant (1985). "Physiological Considerations of Artificial
Gravity." _Applications of Tethers in Space_ (NASA CP 2364),
vol. 1, p. 3.95-3.107. Edited by Alfred C. Cron. NASA Scientific
and Technical Information Branch. Proceedings of a workshop held in
Williamsburg, Virginia, June 15-17, 1983.

--

Ted Hall
  #30  
Old August 25th 03, 06:04 AM
Theodore W. Hall
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Default artificial gravity a different idea...maybe?

Roger Stokes wrote:

One concept that wasn't mentioned was a sleep centrifuge with the
sleeper(s) lying parallel to the rotation axis - like the centrifuge
at six flags magic mountain, but smaller. For example a 2 metre radius
would give 0.5 g at 15 rpm. The rpm is higher than the recommended
maximum of 6rpm, but sleep movements would be much more limited than
waking movements, and would also mostly be co-axial with the rotation.


Yes, but it would also be like bed rest on Earth. It wouldn't load
the weight-bearing bones (especially, the spine and legs) and so would
probably not be very effective against demineralization.

The skeletal system needs axial loading to maintain its "normal"
structure.

--

Ted Hall
 




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