1. Mr. Blue Dot
    Offline

    Mr. Blue Dot Member

    Joined:
    Mar 22, 2011
    Messages:
    87
    Likes Received:
    2
    Location:
    Washington

    Artificial gravity by rotating ring

    Discussion in 'Research' started by Mr. Blue Dot, Mar 27, 2011.

    In the story I'm writing I have a few space stations that have 1.5 mile diameter rings that rotate around a central axle to simulate gravity. There are elevators that run from the "surface" of the ring where the gravity is 1 g and the go up to the axle, which acts as a hallway/tunnel to other areas of the station.

    What I would like to know is, what would somebody traveling in that elevator feel? Would traveling from the center to the ring be different that traveling from the ring to the center? Would someone inside the axle be weightless or not?

    I'm currently at a point in my story where a girl is traveling from the landing bay (weightless section) of the station to an entertainment area on the spinning ring. I'm trying to write what she's experiencing as she's going through different sections of the station, but I'm stuck because I can't really wrap my head around the physics at work here. I appreciate any input on this anybody has :D
     
    1 person likes this.
  2. Ion
    Offline

    Ion Senior Member

    Joined:
    Mar 7, 2011
    Messages:
    138
    Likes Received:
    7
    Gravity would decrease toward the inside of the station. Your 'down' would be toward the exterior of the station, 'up' would be toward the center of the station. At the center, you'd be in a very slowly spinning room with no gravity. You would not spin with this room unless you were holding onto something.

    The smaller the radius of the station, the faster it would have to spin at the center to maintain gravity. A very large station like yours would be spinning relatively slowly at the center, but would be spinning at the same speed along the outside edge as a smaller station.
     
  3. Arathald
    Offline

    Arathald Contributing Member

    Joined:
    Mar 11, 2011
    Messages:
    314
    Likes Received:
    17
    Location:
    Seattle
    To get that force at 1.5 miles out, your station would have to revolve at 0.86 rpm, or about one revolution every 1 minute and 9.8 seconds.

    If you consider that the artificial gravity would increase linearly with radius (i.e. at 0.375 miles up, half the distance between the rim and the hub, a person would experience 0.5g), as someone took the elevator up, they would gradually and steadily go from full gravity to weightlessness, and going from the hub to the outside, they would experience going from weightlessness to 1g.

    You also have to consider any acceleration effects from the elevator -- at the top of the elevator, they would experience negative downward acceleration (it doesn't matter which direction they're going -- they'll either be speeding up going away from the hub or slowing down going towards it), so they would likely have to be strapped in if the acceleration was great enough, or at least have something to hold onto. At the bottom, they would experience acceleration in line with the force of "gravity", so they would feel heavier, just like at the bottom of a normal elevator, but as long as the acceleration was gradual enough that they would be able to stand it normally, you wouldn't need any extra mechanism.

    To see the effects of gravity at any given elevation, you can use this calculator:
    http://www.calctool.org/CALC/phys/newtonian/centrifugal
    You'll want to set your rpm to 0.86, and then the radius will be the distance from the hub (so if you set it to 0.75 miles, the radius of your station, you'll see that the acceleration becomes about 1g).

    [Edit: Sorry, read diameter as radius. Corrected the numbers above.]
     
  4. Mr. Blue Dot
    Offline

    Mr. Blue Dot Member

    Joined:
    Mar 22, 2011
    Messages:
    87
    Likes Received:
    2
    Location:
    Washington
    Thank you! This is exactly what I needed to know. I had been trying to picture a ball traveling down in the elevator to the ring untethered, and I had imagined it as floating near the top of the elevator near the "ceiling" and dropping to the floor at some time during the trip.

    Since the elevator has to travel three quarters of a mile, it will be traveling pretty quickly. It will be a 1-2 minute trip or so from hub to ring (including acceleration/deceleration), I figure, so it will probably be good to strap them in. I don't think a grab bar would quite cut it at that speed.
     
  5. Arathald
    Offline

    Arathald Contributing Member

    Joined:
    Mar 11, 2011
    Messages:
    314
    Likes Received:
    17
    Location:
    Seattle
    Sounds good. You probably also want to figure out exactly what the acceleration curve of the elevator will look like if you want to describe the trip in any detail. 1-2 minutes wouldn't be at all unreasonable at that distance, but depending on how you want to do it, the acceleration might be significant.

    My initial thought is that youd want to accelerate to around 50 mph, and if you imagine doing that in a car, doing that over about 10 seconds doesn't exert a ton of force on a passenger. I'm just pulling these numbers out of my head though; figuring out the actual top speed and the exact accelaration for that is a little more difficult.
     
  6. abelsaywell
    Offline

    abelsaywell Member

    Joined:
    Mar 19, 2011
    Messages:
    16
    Likes Received:
    1
    A nice idea to this might be to have the elevators work in pairs so that one goes towards the middle as one goes to the outer "ring." This way you don't effect the rotational velocity by having a massive elevator moving in and out from the middle. Otherwise, all things being equal, a heavy elevator moving from the middle to the ring would cause the rotational speed to lower.
     
  7. Cogito
    Offline

    Cogito Former Mod, Retired Supporter Contributor

    Joined:
    May 19, 2007
    Messages:
    35,935
    Likes Received:
    2,043
    Location:
    Massachusetts, USA
    Also, if you drop something, it will not fall straight "down", but will follow what looks like a curved path. It wouldn't be particularly noticeable in the one-gee habitat area unless you drop it enough of a distance, but it will be more obvious as you approach the hub.

    It isn't a force. It's an illusion because you, the observer, are constrained to a rotating (non-inertial) viewpoint, whereas the falling object is actually travelling in a straight line. The apparent curve will be toward antispinward.

    Look up Coriolis effect in google, or in a physics textbook.
     

Share This Page