Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 22/03/2016 13:21:48
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David Oehl - Via Facebook asked the Naked Scientists:
Could a spinning space craft be the solution to the problems of micro gravity?
What do you think?
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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.
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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.
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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 (http://en.wikipedia.org/wiki/Bolas). The spin would make it rather difficult to visit the neighbors.
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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.
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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?
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perhaps in the not to distant future we could have spacecraft capable of maintaining 0.2–0.5 G acceleration?
One of the promising prototypes for spacecraft propulsion is the VASIMIR VX-200 (http://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magnetoplasma_Rocket#Development_of_the_200_kW_engine)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).
a spinning space craft
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".