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Author Topic: Can gravity be simulated by spinning a spacecraft?  (Read 3945 times)

Joel Rosner

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Joel Rosner  asked the Naked Scientists:
   
Hi,

I recall learning that we can simulative gravity in space by rotating or spinning the ship or station (essentially, using "centrifugal" force), much like what you see in the movie 2001: A Space Odyssey. 

I understand why that  might not work for the space shuttle or similar craft, but why doesn't the International Space Station use this?

Thanks,
Joel Rosner

What do you think?
« Last Edit: 12/03/2010 05:30:02 by _system »


 

Offline Geezer

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Can gravity be simulated by spinning a spacecraft?
« Reply #1 on: 12/03/2010 05:55:12 »
It would work. But it would also make it a bit tricky to safely connect with other spacecraft. Also, you would not be able to look out the "windows". If you did, you'd probably barf.
 

Offline graham.d

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Can gravity be simulated by spinning a spacecraft?
« Reply #2 on: 12/03/2010 10:29:37 »
To be "acceptable" the diameter has to be quite big. It is just a matter of engineering and any permanent spacestation would probably employ such a system as long periods in zero gravity are not good for health. It would not have to be as solid a construction as in the film 2001, but could be any two constructions connected to each other via a strong tether and then rotating round each other with the tether in tension. The advantage of a central area is, as shown in 2001, is that it enables docking of spacecraft by simply matching the rotations of the craft to the spacestation. The more solid construction also then allows movement between the central region and the extremes. I think the 2001 ideas (formerly in Dan Dare comic strips) were pretty good, if expensive.
 

Offline LeeE

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Can gravity be simulated by spinning a spacecraft?
« Reply #3 on: 12/03/2010 18:36:19 »
In addition to the diameter of the centrifuge needing to be quite big, it also needs to be anchored to a correspondingly large structure, for unless the centrifuge is carefully balanced when running, it'll exert some very undesirable forces upon the parent structure.  The parent structure also needs to be much bigger than the centrifuge because starting and stopping it will impart a rotation to the parent structure.

In short, the ISS is too small and too fragile for a usable centrifuge.
 

Offline wolfekeeper

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Can gravity be simulated by spinning a spacecraft?
« Reply #4 on: 12/03/2010 18:37:06 »
The ISS itself doesn't spin because most of the experiments require zero-g; that's the main purpose of it being there(!) The structure is probably more or less already strong enough; the loads due to the atmospheric pressure are generally much bigger.

There was a proposal to put a centrifuge in the ISS to try to find out how much gravity animals need to avoid their bones progressively turning to mush; but it got cancelled for budgetary reasons.

All long-term experience with gravity has been at 0g or 1g; the astonauts weren't on the moon long enough to find anything useful out. It may be that neither the Moon (1/6 g), nor Mars' (1/3 g) gravity is enough for long term habitation.
« Last Edit: 12/03/2010 18:40:03 by wolfekeeper »
 

Offline graham.d

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Can gravity be simulated by spinning a spacecraft?
« Reply #5 on: 12/03/2010 20:27:31 »
Lee, there doesn't need to be a parent structure that has much strength. Two equal masses could be tethered via relatively thin but strong steel cables. If reasonably the same mass in each they will, if set in motion, rotate about some midpoint. A structure connected to the cables at the midpoint need not experience any significant forces.
 

Offline LeeE

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Can gravity be simulated by spinning a spacecraft?
« Reply #6 on: 13/03/2010 19:44:50 »
Well, either you balance the loads carefully, or you have to be able to re-position the rotation/anchor point along the tether/arm, just as carefully.  Think about how important it is to balance your car (automobile) wheels (by just a matter of a few grammes).  While the centrifuge would be rotating much more slowly than your car wheel, it'll have much greater mass and eventually it'll lead to metal fatigue as it tries to bend/move the entire structure back and forth.
 

Offline graham.d

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Can gravity be simulated by spinning a spacecraft?
« Reply #7 on: 13/03/2010 19:53:11 »
I didn't say it was easy :-) It's just that a central structure need not take any significant load. Cables, usually stainless steel, are used in a lot af major building constructions nowadays. I'm not sure about use in space, but I am sure there is some material that can be used or the steel protected in some way. Anyway, it was the principle I was concerned with.
 

Offline LeeE

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Can gravity be simulated by spinning a spacecraft?
« Reply #8 on: 13/03/2010 20:04:57 »
Heh! ;)  I think it's probably fair to say that nothing mechanical is easy in space, from vacuum welding issues, to freezing/evaporating lubricants, to cosmic ray alteration of the materials.

There's nothing wrong with the principles of centrifuges in space, just the practical implementation of them.
 

Offline wolfekeeper

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Can gravity be simulated by spinning a spacecraft?
« Reply #9 on: 22/06/2010 21:01:16 »
The main trick is to make sure that the structure is a fairly flat shape, so for example triangulate three masses. If it's flat it won't wobble much at all; you can damp it right out.

Wheels on cars aren't a very good example. With a wheel you're trying to force a mass to rotate about a particular axis, which isn't ever going to be quite at the centre of mass. Doing that can cause cyclic forces on the bearings which are felt as vibrations.

But with a space station, there's no bearings, it will spin around it's centre of mass without any vibration.

The only thing you want to watch out for is very asymmetric masses, as that can cause tumbling motions, like lumpy asteroids for example. But provided the aspect ratio of the object is less than about 4:1 IRC space stations/ships shouldn't wobble significantly.

The main problems with spinning stuff is how it interacts with the main drive axis and if you want zero-g.
« Last Edit: 22/06/2010 21:06:01 by wolfekeeper »
 

Offline syhprum

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Can gravity be simulated by spinning a spacecraft?
« Reply #10 on: 22/06/2010 22:03:55 »
I understand the ISS is to be scrapped in about 10 years, maybe the Chinese will put up a bigger and better one incorporating some of these principles.
 

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Can gravity be simulated by spinning a spacecraft?
« Reply #10 on: 22/06/2010 22:03:55 »

 

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