Science Questions

Could a spinning space craft be the solution to the problems of micro gravity?

Tue, 22nd Mar 2016

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Question

David Oehl asked:

Could a spinning space craft be the solution to the problems of micro gravity?

Answer

Physicist Dave Ansell had a spin at answering David Oehl's question... The International Space Station

Dave - Microgravity is really bad for you because all sorts of things stop working.  Your bones get very, very weak, your muscles get very, very weak.

Chris - What does it actually mean?

Dave - Microgravity, - if you’re in space, if you’re in orbit you’re just free falling which means that everything is falling with you which means that you’re effectively weightless because everything is falling at exactly the same speed as you are.  So you can push off and float around - really quite fun but quite unhealthy.  So the suggestion and it’s actually been suggested for a long time (it might have been Arthur C. Clarke who came up with it)...

Chris - 2001: A Space Odyssey had a spinning space station.

Dave - A spinning space station because if you get a bucket and spin it round your head, then you need to apply a force to pull it in to keep it going in a circle…

Chris - But the evidence is if you fill it with water, the water doesn't come out…

Dave - Doesn't fall out.  So basically you change the direction of gravity, and if you’re in space the same thing happens and you’d create artificial gravity.

Chris - So if you had a big ring that was spinning, the person standing in one part of that ring in the same way as the fairground ride creates a sort of centrifugal effect, you feel thrown outwards and the ride pushes you back in to stop you flying off, the space station would, effectively, push up through the floor at you?

Dave - Yes. I think the reason why they haven’t done it so far is that you either need to spin very, very fast or you need to be very, very big and that makes everything very heavy and basically, no-ones build a space station big enough or had people up there long enough to make it worthwhile doing it.

Chris - So if you had something very small that was turning very fast would that, nonetheless, whilst making some gravity make people feel extremely unwell whereas the rationale would be if you make it very big, the sense of rotation for a person would be smaller but they’d still, nonetheless, get the effect?

Dave - You probably would feel quite uncomfortable because, apart from anything else, everything would behave very, very strangely because you would get not just the centrifugal force, you get what’s called the coriolis force so if you threw something into the middle of a spaceship it would actually spin round and end up going in a completely different direction from one you’d expect it to be.  I don’t know at what point it’s actually worth doing this.  Certainly there has been talk of doing it if you’re sending someone to Mars over a few months if they’re still in one piece to get there but certainly so far, no-one’s tried.

 

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Yes but we do not currently have the resources to properly execute such an engineering feat.
And I can not see us acquiring such resources in the near future.
If it was to be done, it would have to be done properly. And by properly I mean at the scale of "Rama"  by Arthur C. Clarke.
arthur.manousakis, Fri, 5th Feb 2016

If microgravity is a problem, then obviously spinning a vehicle will produce a consistent outward force. However it isn't a problem except for spiders and some plants (though I do wonder about fish - does anyone have any information?) and the majority of space experiments are designed to exploit microgravity. 

Most humans adapt to free fall in a day or so, and if you want to look out of the window of a small rocket, it helps if it isn't spinning. In the case of a very large space station, however, the formula  F= 2πmr/t where r is the radius of the station and t is the time taken to complete one revolution, suggests that we might usefully generate a radial acceleration of about 0.1g with a fairly comfortable rotation period, like a rotating restaurant (do they have asymmetric soup plates?). This would make housekeeping  a lot easier as stuff would eventually fall to the floor but not so hard as to break, thus making life tolerable for clumsy scientists like me, and interesting for my dog. alancalverd, Fri, 5th Feb 2016

If the goal is to reduce muscle and bone wastage, a moderate acceleration would be useful - perhaps Mars surface gravity?

Thinking slightly smaller than Rama, have a look at the spinning wheel of the spaceship in "2001 A Space Odyssey", or "The Martian".

Even smaller still, the book "Seven Eves" suggests that you could connect two small spacecraft by a strong tether, and set them spinning, like bolas. The spin would make it rather difficult to visit the neighbors. evan_au, Fri, 5th Feb 2016

Biggest issue is that it really needs to be large to make the difference in Coriolis force between your feet and head small, so you need big, which in turn means the diameter has to be large. Just tethering leads to a problem with mass shifting in the occupied cabin causing the mass centre to move along the tether, so unless you really have a good control system your tether will be very unstable, probably spinning out of control during the spin up phase. will never be stable, you will always need power and reaction mass or moving masses to balance it, and that will be unreliable and unsafe.

Add to that a small unit will be hard to dock to, you need a large mass so you can have a descent method ( lift or stairs) that will not affect balance. SeanB, Sun, 7th Feb 2016

If the spacecraft is intended for traveling long distances, then it could accelerate at a constant rate until the mid point, turn 180°, and then decelerate at the same rate until it arrives at the desired endpoint. We might not yet be able to build spacecraft that can accelerate at 1G for weeks/months/years, but perhaps in the not to distant future we could have spacecraft capable of maintaining 0.2–0.5 G acceleration? chiralSPO, Sun, 7th Feb 2016


One of the promising prototypes for spacecraft propulsion is the VASIMIR VX-200 ion rocket.

It consumes 200kW of electricity, and has a thrust of 5 Newtons (half a kilogram force). It looks like it has a mass of several hundred kg. Add a few tons of reaction mass and a source of electricity, and it looks like 0.1% G is more likely in the near future (unfortunately).


If you want to think really big, Larry Niven's fictional "Ringworld" would provide 1G gravity for a very large area, with a star in the middle. This idea seems to form part of the backdrop to the computer game "Halo" (just look up in the sky...). Unfortunately, this is not very mobile.

To imagine a super-large traveling spaceship with reasonable gravity, see Gregory Benford's novel "ShipStar".
evan_au, Mon, 8th Feb 2016

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