Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

2 Space Elevators?

  1. Mar 23, 2012 #1
    Hello

    I am new to thinking about these kinds of things so please forgive me if what I suggest is pure nonsense LOL!

    As I understand it the main problem with building the traditional model of a space elevator is a practical one based on the difficulty in manufacturing a cable made of nanocarbon which can support its own weight below geostationary orbit.

    Perhaps there is a way around this. Perhaps we can develop a model which reduces, or nearly eliminates the payload on the cable.

    If we were to build 2 space elevators, one on either side of the Earth in perfect balance, with a land and ocean based cable circling the Earth and connecting the two, wouldn't that neutralize the payload on the cable? That way we could possibly construct the cable out of more traditional materials, like kevlar??

    Thanks
     
  2. jcsd
  3. Mar 23, 2012 #2
    How would that neutralize the payload? Gravity is pulling down. A cable pulling sideways would not help anything. And I don't think you appreciate how big the earth it. A cable long enough to go all the way around the earth to connect two elevators in the air would sag till it touched the earth and snap under its own weight in the process.
     
  4. Mar 23, 2012 #3
    Thanks very much for the reply.

    I was thinking the two space elevators would be exactly opposite from each other, on either ends of the Earth so that the effects of gravity and centrifugal force would be in equilibrium.

    The cable would wrap around the Earth on the ground, not in the air and shouldn't snap due to the equilibrium of the system (I'm trying my best here lol). If the circumference of the Earth is 40,000 km we would be adding, from what I understand, about 20% more cable, which, if made out of something other than carbon nanotubes, might very well be feasible.
     
    Last edited: Mar 23, 2012
  5. Mar 23, 2012 #4

    russ_watters

    User Avatar

    Staff: Mentor

    Welcome to PF!

    In equilibrium may mean all forces sum to zero, but it doesn't mean the forces go away. A space elevator would on its own be in a similar equilibrium to what you describe.
     
  6. Mar 23, 2012 #5
    If I understand correctly a space elevator on its own would still require a cable that could support its own weight below geostationary orbit.

    But if you have two counterweights on opposite sides of the Earth, out in space, connected, then this is no longer an issue and a cable can be made of more typical materials.

    thanks for the welcome btw!
     
  7. Mar 23, 2012 #6
    Here are some diagrams to help explain my thinking:
     

    Attached Files:

    • 002.jpg
      002.jpg
      File size:
      8 KB
      Views:
      104
    • 003.jpg
      003.jpg
      File size:
      9.2 KB
      Views:
      103
  8. Mar 23, 2012 #7

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Oh, we understand your way of thinking alright. What we are telling you is that you are "solving" a little problem by making a bigger one.
     
  9. Mar 23, 2012 #8
    I suppose if problem A is solvable in 100 years and problem B is solvable in 10, then problem b would be smaller.
     
  10. Mar 23, 2012 #9

    Drakkith

    User Avatar

    Staff: Mentor

    Problem B is not solvable in 10 years. It's even more of an engineering challenge than a single elevator.
     
  11. Mar 24, 2012 #10
    If you have 2 equal teams playing tug-of-war the forces on the rope are equal and opposite so the total force on the rope is zero. That's why the rope does not move. That does not mean that the tension on the rope is zero. The situation you are describing is similar. The problem with building a space elevator is making a rope that will withstand the tension.
     
  12. Mar 24, 2012 #11
    OK but the main difference here is that the counterweights are in a fixed orbit in space around the Eath and therefore they don't pull very much on the cable, they simply keep it in place.
     
  13. Mar 24, 2012 #12
    Why?
     
  14. Mar 24, 2012 #13
    The only difference is the useless rope around the world.
     
  15. Mar 24, 2012 #14
    :eek: *carry the 2 LOL!
     
  16. Mar 24, 2012 #15

    sophiecentaur

    User Avatar
    Science Advisor
    Gold Member

    Each tether still has its own mass and, hence, its own weight which needs to be supported by the tension in the rope. This applies however many tethers are involved and is the reason why the space elevator is not yet doable.
     
  17. Mar 24, 2012 #16

    russ_watters

    User Avatar

    Staff: Mentor

    This simply isn't true. In both cases, the counterweights support exactly the same weight: The weight of the cable from the counterweight to the ground. Your case has the added issue of a cable around the earth that since it is parallel to the earth's surface is supporting no weight at all. The added piece of your idea doesn't actually do anything at all.
    Uh huh.....in that cable around the earth, where it meets the space elevator: what direction is the force on the space elevator? Up or down?
     
  18. Mar 24, 2012 #17
    What if we drill a hole through the Earth? Would that help anything? :rofl:
     
  19. Mar 24, 2012 #18

    davenn

    User Avatar
    Science Advisor
    Gold Member

    No, cuz the outer core is very hot and molten. Nothing is going to survive going through there, and the inner core is solid nickel / iron ya ain't going to drill through that

    Dave
     
  20. Mar 24, 2012 #19

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Layering impractical idea upon impractical idea will not lead to a solution. It also pretty much defines "overly speculative".
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: 2 Space Elevators?
  1. Space elevator (Replies: 3)

  2. Space elevator (Replies: 16)

Loading...