Artificial gravity inside a planet's atmosphere

Discussion in 'Science' started by yanman, Jul 15, 2007.

  1. yanman

    yanman Member

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    My question is from thinking about space stations and how they'd ideally be spun to create artificial gravity, keeping the crew's muscle/bone health etc.

    Say this space station was fairly mobile, i.e. ion propulsion, maybe nuclear powered and was able to come inside a planet's atmosphere.

    If you're creating say 1g of artificial gravity in the space station (spoke shaped so anywhere on the spoke would experience 1g of gravitational force in the direction of the centre of the spoke), what would the gravity felt by the crew be once the station entered earths orbit for instance?.. would it be (1 + x)g where x is the gravitational force of earth at that position?
     
  2. noboundaries-au

    noboundaries-au Member

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    In orbit, it still be the same AFAIK, orbiting is like a continual freefall where you dont lose height.

    If it was falling directly towards earth, the same, until it hit atmosphere and slowed down i guess

    If it was at a stop in the atmosphere or in space, with thrusters keeping it in the exact same spot. You would experience an offset equal the gravity of the earth at that spot i guess. So the closer end of the ring would be 2g and the top would be weightless if at about ground level. Itd be akin to one of those spinny things at a town show, except the ship would possibly spin slower.
     
  3. evil-mooo

    evil-mooo Member

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    People tend to misunderstand the concept of gravity. It is a common belief that in "space", there is no gravity and that is why everything is weightless. However, 100km up, the gravitational force from the earth is still very strong. Gravitational acceleration is still in the order of about 8 m/s^2.

    The reason everything is weightless is because an orbit is a constant state of freefall, so there are no reaction forces pushing back on anything to give it "weight". They are, however, still experiencing a strong gravitational force.
     
  4. dc0079

    dc0079 Member

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    And the weightlessness is due to the relativity to their surrounding.
     
  5. Assasinator_2

    Assasinator_2 (Banned or Deleted)

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    Firstly, spinning a spacecraft that is circular to simulate gravity, creates an acceleration away from the centre of the craft, as it's just a centrifugal force acting outwards.

    Secondly, if you're doing that 'inside an atmosphere', disregarding waht evil-mooo said, you're either going to create your centrifugal force 90 degrees to gravity by spinning it as a flat disc in the air (not unlike your typical idea of a flying saucer, and accelerating outwards towards the horizon) OR you're gonna do it on its side, so at the bottom you have extra gravity (wehn gravity and centrifugal force are acting downards), but that means at the top you'll have less as they'll be working opposed to one another (centrifugal force upwards, gravity downwards).
    What i'm getitng at here, is baiscally that you cannot just say the overal acceleration felt on a person will be in one dimension, but rather you'll have a component that is always towards the centre of the earth, and a component that will always be directly outwards from the centre of the spinning craft. Sometimes they'll be in line (the two cases I described above) and at all other times, they'll be at some angle between 0-90 degrees out of line (with the extreme being when one is at right angles to the other).

    Thirdly, isn't this what a centrifuge is? :p

    What do you mean by that?
     
    Last edited: Jul 15, 2007
  6. OP
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    yanman

    yanman Member

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    ah yeah of course. i was forgetting to think of it as two 3-dimensional vectors. the artificial gravity in an x,y,z direction towards earth's centre and an x,y,z outwards (as someone corrected me) from the centre of the space station.

    hmm so on that last point, if you wanted to have a long corridor on the space station that ran the circumference, people would be walking on the inside rim if the artificial gravity was outwards from the core, is that correct?
     
  7. wahoo84

    wahoo84 Member

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    yes of course, otherwise u'd just float off :)

    Try the experiment where u hold a bucket of water and continually rotate ur arm and bucket over ur head (don't stop though...), the water doesn't come out due to the centrifugal force generated.
     
  8. OP
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    yanman

    yanman Member

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    aah how could i forget the bucket of water :p
     
  9. Black Shadow

    Black Shadow Member

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    completely the opposite in fact, there is zero force that will push any part of the spacecraft directly out away from the centre of mass, instead there is a force (tension) between the particles of the craft that pull towards the centre of mass of the craft. If some part of the craft were to be detached from the rotating craft it would simply move at a tangent to the orbital path at that point as there is no longer a force acting upon it and will move in a straight line.

    the force is known as Centripetal Force and centrifugal force is misunderstanding of the real force in play (tension - centripetal force/towards centre)
     
    Last edited: Jul 15, 2007
  10. Assasinator_2

    Assasinator_2 (Banned or Deleted)

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    I like how xkcd put it best
     
  11. molloby

    molloby Member

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  12. OP
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    yanman

    yanman Member

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    I preferred the wiki to help understand :p
     
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    yanman

    yanman Member

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    Wow checkout all this info
     
  14. boron boy

    boron boy Member

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    Don't forget that the force would be stronger the further you are away from the centre of the station. At the exact centre point it would be zero. It's like on a merry-go-round - if you stand in the middle there's not much pull, but out on the edges you'll vomit in no time.

    It's interesting to think what would happen if such a station entered the atmosphere as you suggested, however I'm sure the small change in gravity would be the last thing on their minds as they burn to a crisp!

    Oh and thanks for that site, on artificial gravity, interesting read.
     
  15. 2xCPU

    2xCPU Member

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    If anyone is still having trouble visualising what happens, watch 2001. It's very well displayed.

    2.
     
  16. Zylatis

    Zylatis Member

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    I think you'll find its probably much closer to g than that, 100km isnt that far for the gravitational force.
     
  17. OP
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    yanman

    yanman Member

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    though even as low as 0.5g it'd still be a significant force

    my original question i see now is about a compound of two sets of forces, the artificial and the gravitational force of the large mass - earth :p seems that if you want to have a space craft that simulated gravity by spinning then it'd be tricky once under other gravitational forces like when close to a planet. i wonder if it's even possible to modify the space craft's spin to sustain a consistent feeling weight for the crew.

    the best designs seem to be rings such as in Halo or in Culture novels by Banks (or Ringworld etc), where standing on any of the usable space you should experience the same weight, though in those stories they all orbit stars and are massive :p
     
  18. evil-mooo

    evil-mooo Member

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    Yes, you're right. I just went and did the calculations. It'll be around 9.5 m/s^2.

    I was just trying to make a point about gravity still existing in space, and that weightlessness is not caused by a lack of gravitational force.

    If the spacecraft was in orbit (which is the only reasonable way to keep it up there), then the gravitational pull of the earth would not be felt, and only the simulated gravity from the spinning of the ring-shaped craft would be felt.
     
    Last edited: Jul 17, 2007
  19. patto

    patto Member

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    As has already been said this is not an issue.

    Remember you cannot feel the force of gravity. On earth we do feel the force of gravity we simply feel the force of the ground pushing up on us. In a floating/orbiting space ship people are weightless, no matter how strong the actual gravitational field is. (unless an external, non gravitational force is applied to the spaceship)

    In a spinning space ship there are centripetal forces on the spaceship and the spaceship exerts centipetal forces on the occupants which you feel as gravity.
     
  20. Zylatis

    Zylatis Member

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    So long as the ship is 'falling' at the same rate, the gravitational pull will not be felt and there will be no weight. If you wanted to make the artificial gravity equal in all areas you could make it spin in a direction perpendicular to that of the force line, or parallel (even though its curved but anyway) to the surface of the earth.
     

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