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Gravity on a space evelvator

  1. Sep 18, 2012 #1
    I've been reading a lot about space elevators being built from carbon nanotube thread and having lifters powered by lasers. I'm imagining it to be 50,000 long. Obviously this is fiction at the moment, but i was wondering...

    if there was such a structure, what would be the effects of gravity on someone in a lifter?
    At what point would the effects be felt?
    As the lifter was pushed/pulled further along the ribbon, how would gravity's force change along the journey.

    Also what kind of speed do you think would be reached on a 50,000 km long cable?
  2. jcsd
  3. Sep 18, 2012 #2


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    The passenger would weigh less and less, reaching weightlessness at the height of ~35800km(geosynchronous orbit), and then get heavier again, with the upper limit depending on the cable length.

    The maximum speed of the climber would be constrained by the thermal tolerance of the climber/ribbon.
    This publication:
    describes a climber going at 200km/h, but that is the cable-deployment vehicle, so perhaps the payload-carrying version could have a different, faster design.
  4. Sep 18, 2012 #3
    Thanks the reply and for that publication, looks very interesting.

    Is the 35800km the point where Earths gravity has lost effect?

    Also what if the ladder was going toward the moon? would the passenger feel the weight again as he got closer to the moon?

    Would there be a Lagrangian point and would that effect?
  5. Sep 18, 2012 #4


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    That point does not exist, the gravitational force from earth is everywhere (but quite weak in large distances).
    35800km is the point where the gravitational force is just enough to keep an object in an orbit with a period of 1 day (= the movement of the space elevator itself)

    The moon needs much more time for an orbit, you cannot connect a space elevator to the moon (or extend it so far that the moon's gravity becomes important).

    Lagrangian points refer to objects with the same orbital period - which would be about one month for moon, and not one day for the space elevator.
  6. Sep 30, 2012 #5
    Doesn't the upward velocity of the elevator itself create an artificial gravity that has to be factored into these calculations?
  7. Sep 30, 2012 #6


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    Only if it is accelerating.
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