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Gravity in space

Posted by: Stefan Sigwarth - Sat Aug 21, 2004 11:30 am
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Gravity in space 
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Post    Posted on: Tue Aug 24, 2004 2:09 am
Oh, and one other random point...

There's very likely a limit as to how fast you can be rotating, long term, without discomfort.

There's a variety of numbers and we really don't know (and even the centerfuge module on the ISS wouldn't give us good answers), but there's some stuff at http://yarchive.net/space/spacecraft/artificial_gravity.html that talks about it.


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Post    Posted on: Tue Aug 24, 2004 7:13 am
Hello, spacecowboy,

I have to read the relevant capital of my book again, but as I remember the effect of gravity on time has nothing to do with dilatation of time. Only the result is identical. When I've found the relevant capital I'll post the contents here translated to English.



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Post    Posted on: Tue Aug 24, 2004 9:48 am
So what sort of speeds of rotation / sizes are we likely to see in the torus scenario?

Do people think that a small amount of artificial gravity will be acceptable, so that on a space station you will see a artificial gravity similar to that on the moon? Or is it going to be something closer to Earth's 9.8ms-2 (or whatever).

And I'm right in thinking that the outside edge of the torus will be the floor, right?

/Dan :)


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Post    Posted on: Tue Aug 24, 2004 10:13 am
You're right -the outside edge will be the floor.

The speed may be changeable as is sometimes thought to be advantages if the torus is part of a spaceship to travel between Earth and Mars, the moon and Mars or Earth and the moon. The changeablity is providing the possiblity to become used to the different gravity of the target planet.

If the torus is connected to a center there might be a maximum artificial gravity depending on the maximum tense the connecting parts are fit to I suppose.



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Post    Posted on: Tue Aug 24, 2004 11:50 am
Thanks :-)


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Post    Posted on: Tue Aug 24, 2004 5:24 pm
spacecowboy wrote:
Ekkehard Augustin wrote:
<snip>


You got it backwards. Time dilation is caused by speed, not gravity. As your speed approaches the speed of light, the outside world seems to slow down (please note that to the outside world, you appear to slow down).

109Ace: I thought that the Coriolis force could be reduced to within acceptable limits in a reasonably-sized station, but don't quote me on that.


according to the general theory of relativity, gravity affects time and space.I think it slows down time but I can't recall for sure. Any material on black holse will explain these effects in detail.

I don't think simulating gravity through rotation, and its effects on human beings has ever been attempted in space. correct me if I'm wrong.

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Post    Posted on: Wed Aug 25, 2004 5:06 am
Hmm, nice thread. I have a vested interest here.

Me and my fiance were having a discussion one day (my fiance is a soon to be physiotherapist) and I asked her whether she'd be interested in one day living in space.

I was taken aback when her response was "no way!"

Apparently she'd studied briefly the terrible effects that a weightless environment could have on your body and she had never heard of the ways of generating gravity as mentioned here.

Perhaps it could be a good point of post graduate study when I build her a torus.


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Post    Posted on: Thu Aug 26, 2004 9:28 am
There's an alternative concerning the different gravity at the planets to add.

Instead of changing the velocity of rotation there might be several toruses connected together by tunnels. Then the most inner torus has artificial gravity of the smallest planet and the most outer torus has that of the biggest planet.

This could be combined with changeability of rotation velocity.

Besides - because of the elevator-like parts of these concepts at planets with less than earthian gravity a habitat with earthian gravity could be established as an integral part of the cable an elevator requires to climb to the orbits. It only has to be at sufficient altitude. For the problems please refer to the elevator-related discussions at this board. May be that the habitats one day can form a torus around the equator of that planet - or sections of a torus - connected to the surface by several cables.



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Post    Posted on: Thu Aug 26, 2004 12:15 pm
so you could put people born on ganymede,mars and earth in the same space station?
i think genetic engineering will solve the problem of adaptability to different Gs

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Post    Posted on: Thu Aug 26, 2004 12:20 pm
109Ace wrote:
so you could put people born on ganymede,mars and earth in the same space station?
i think genetic engineering will solve the problem of adaptability to different Gs


Nanotech and stuff like UC Berkeley's exoskeleton should help take care of that... Genetics tend to be rather permanent (or, at least as far as I know of), which kinda sucks if you wanna go back home.

In any case, yes: such a station would also serve as a controlled training environment for people who are traveling to other planets.

Oh, and you're right with the gravity-effects-time thing, but something tells me it's basically irrelevant unless you're dealing with insanely high gravity (such as that near black holes). Of course, the matter falling into the black hole could simply be accelerating towards lightspeed, in which case gravity has no direct effect on time.

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Post    Posted on: Tue Aug 31, 2004 5:52 am
I was thinking of another problem for this. Since there is no gravity in space how would you be able to walk around a ship without disturbing its rotation/course and/or whatever else is influenced?

I saw a documentary lately about Apollo 11 and it was stated that if you'd moved an inch in the lander module, you would completely shift the balance of the vehicle.

Is this true, and if it is, does it matter if an object ways 1 kg or 1000 kg to change its balance?


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Post    Posted on: Tue Aug 31, 2004 7:16 am
I may be wrong but I suppose the answer again is provided by the equivalency of gravity to acceleration.

Under gravity - at earth for example - the influence of a man walking along the surface on the movement of earth is depending on the relation of the gravity of his body at the one side to the gravity of earth on the other side.

In psace this relation completely will be substituted by the relation of the acceleration of the man's body to the acceleration of the torus.

Once artificial gravity ist established the man's body will be accelerated by the rotation. For simulation earthian gravity the velocity of the rotation will have to be relatively fast in comparison to the velocity the Man's body is floating through space to cause sufficient acceleration of that body to new directions permanently.

Comparisons to Apollo seem to be invalid because Apollo hasn't been rotating to cause artificial gravity. The crew has been floating weightless and thus was influencing the vehicle like impacting asteroids. That can't be compared to a spacecraft having a rotating torus for articial gravity.



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Post    Posted on: Tue Aug 31, 2004 3:38 pm
siggy wrote:
I was thinking of another problem for this. Since there is no gravity in space how would you be able to walk around a ship without disturbing its rotation/course and/or whatever else is influenced?

I saw a documentary lately about Apollo 11 and it was stated that if you'd moved an inch in the lander module, you would completely shift the balance of the vehicle.

Is this true, and if it is, does it matter if an object ways 1 kg or 1000 kg to change its balance?


Good job, siggy! You've hit on the fact that while gravity is pretty much irrelevant in free fall (it's not that there's no gravity, just that everything's falling in the same direction all the time), mass is most definitely not.

The answer to your question:
Yes, it does. Newton's First Law of Motion (go here for a good reference) means that if a small object at low relative velocity (a person walking inside a space station) hits (actually, applies a force to, but it's close enough) a big, relatively stationary object (the space station that the person's walking inside of), the big object will move -- there's nothing you can do about that. However, the big object ain't gonna move all that much.

Example: when Voyager 1 slingshotted around the planet Jupiter on its way out of the Solar System, it actually slowed Jupiter down a bit. As a matter of fact, Jupiter will lose ground by about a centimeter -- every few million years.

Knowing this, we can now take Newton's First Law and turn it into an engineering maxim:
Big stuff is hard to move, and small stuff is easy to move. Thus, make things that you don't want moving big enough that they (usually) won't; and make things that you want to move small enough that they can do it easily.

The reason the LM was so easily moved around is that is was designed to have the absolute minimum mass: whatever mass was added for stability had to also be hauled up by the Saturn V (which was already close to pushing its payload limit). So, because the human crew was a fairly large fraction of the LM's weight, any change in the humans' positions had noticeable effects on the LM.

The one and only way to avoid people from moving their spaceship around is to make the vehicle (or station) massive enough (example: weld 3-cm lead plates on the outer hull) to make any change in the center of mass caused by a measly 80-kg human negligible.

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Post    Posted on: Tue Aug 31, 2004 4:37 pm
( Thanks for the information :) )

Mmm, in that case a station would have to make regular changes in its orbit to maintain altitude and rotation.

We'll just have to wait for a decent way to lift large payloads into orbit.... (to make this work efficiently)


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Post    Posted on: Thu Sep 02, 2004 12:23 pm
siggy wrote:
( Thanks for the information :) )


You're quite welcome.

siggy wrote:
Mmm, in that case a station would have to make regular changes in its orbit to maintain altitude and rotation.


Yes, but really really tiny ones.

siggy wrote:
We'll just have to wait for a decent way to lift large payloads into orbit.... (to make this work efficiently)


.....Hence the X Prize and the consequent X Cup.

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