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Space Elevator...

Discussion in 'SpaceX' started by nwdiver, Apr 8, 2016.

  1. nwdiver

    nwdiver Active Member

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    Kurzgesagt put a video together explaining the concept of a space elevator... I brought the concept up at work once and my co-workers acted like I was talking about cold fusion... It would be challenging but not impossible...

     
  2. ggr

    ggr Roadster R80 537, SigS P85 29

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    It says the elevator would be cost effective after launching 1e6 tons, "about twice the weight of the space station". If he's talking about the ISS, it masses
    so he's out by three orders of magnitude I'm afraid, since two of them would be about 1e3 tons.
     
  3. nwdiver

    nwdiver Active Member

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    Hmmm... I wonder if he meant 1M kg?

    But.... any specific discussions about cost are mostly academic at this point since as the video mentions we'll need materials that currently either don't exist or aren't produced at scale. It's an interesting concept... especially thinking about what happens if the tether breaks... a 36k km cable wrapping around the planet would make a mess...
     
  4. ecarfan

    ecarfan Well-Known Member

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    This concept has been written about extensively for decades by science fiction writers, including Arthur C. Clarke. Not a new idea.
     
  5. Johan

    Johan Took a TSLA bear test. Came back negative.

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    Elon laughs at it.
     
  6. Johan

    Johan Took a TSLA bear test. Came back negative.

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    image.jpeg
     
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  7. GlmnAlyAirCar

    GlmnAlyAirCar Member

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    Conceptually it's simple and elegant. From an engineering standpoint, it's a nightmare and simply not possible with today's materials and building techniques.
     
  8. Grendal

    Grendal Active Member

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    The problem with space elevators, if you actually had the materials to build one, are that they are highly unstable. They are using huge mass and huge amounts of potential energy. Since the tether is so long you have to deal with vibrations. Even a very minor vibration can have catastrophic consequences over such a large structure. It's similar to what an architect has to deal with in building a skyscraper. What happens if there is 100 MPH winds? Here is an example of the type of thing I'm commenting on:



    Now multiply that by 100 to 1000 and we are talking about the forces the space elevator would be facing.
     
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  9. nwdiver

    nwdiver Active Member

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    Yeah... there is a materials issue... the idea of building a lunar space elevator first sounds like a good idea... sounds like Kevlar might work there since the gravity is so much lower... still decades away...
     
  10. jkn

    jkn Member

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    Building a space elevator starts with a lunar elevator by 2020
    'Liftport is currently focusing all its energy on building a lunar elevator by the end of this decade.'

    Storm would not cause enormous problem for Earth space elevator, because it will push only lowest 10 km of 40 000 km cable. Trash on orbit causes larger problem.
     
  11. nwdiver

    nwdiver Active Member

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    I forgot that the moon is tidally locked to the earth... so a space elevator on the moon wouldn't use centrifugal force to stay in place... it would depend on the Earths gravity. It would also be MUCH longer... 150k mile tether vs 36k mile tether for a Terran elevator.
     
  12. ggr

    ggr Roadster R80 537, SigS P85 29

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    Hmm, you made me do homework! Basically you would need the space end to be on the earth side of the L1 point. That way the earth's gravity would be continuously pulling it away from the moon, keeping the tether tight. The L1 point moves in and out, as the moon's orbit is elliptical; the maximum distance from the center of the moon is a bit over 60 000km. So a 70 000km tether should do just fine. How did you come up with your number?
     
  13. nwdiver

    nwdiver Active Member

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    From the article...

    'This isn't your average ribbon, though. It will stretch 250,000 km (155,350 mi) towards Earth, where a counterweight within our planet's gravity well will help keep it taut.'
     
  14. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    Wouldn't it require some hellish tensile strength since the moon is moving away from the earth?
     
  15. Saghost

    Saghost Active Member

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    The problem with a beanstalk type elevator (in addition to the technical challenges of building it) is that if it ever breaks, the end coming down has huge amounts of kinetic energy - like as in more than the asteroid that we think wiped out the dinosaurs. It'll wrap around the equator a couple times and do massive damage.

    A more interesting and less impossible and dangerous suggestion (but still very difficult and probably somewhat beyond our present capacities) I saw was the vacuum tower railgun. The theory was that if you can build a structure that's ~90 miles high, you can pump most or all of the air out of it - and because the only path in is in the stratosphere/ionosphere, it won't fill up very quickly.

    That gives you a chance to launch something with much less air resistance - and if you take advantage of the structure with a rail gun, you can get it to orbital altitudes with no reaction thrust. Of course, you still need to accelerate it into orbit, but it'd cut the fuel/power requirements quite a bit (and let the rockets be optimized for a vacuum environment, instead of choosing compromises for different operating pressures.)
    Walter
     
  16. Grendal

    Grendal Active Member

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    Sounds a bit like a space hyper loop.
     
  17. nwdiver

    nwdiver Active Member

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    I wonder if you could do the same thing with the tether... if it was honeycombed you could potentially make it lighter than air or at least a low enough density that if the tether broke it would make a mess but wouldn't cause a lot of damage.

    The primary benefit appears to be the orbital speed you attain by climbing into geostationary orbit. ~90 miles would be a large fraction of the cost but a small fraction of the benefit of ~36k miles...
     
  18. RDoc

    RDoc S85D

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    An Earth based space elevator is likely a 22nd century project, the materials are just not there yet, plus there are a bunch of serious safety issues.

    A lunar elevator is a very different matter since there are already a few materials, e.g. spectra, that are strong enough. An interesting version of this is one with side catenaries that end at the poles, which may be the most interesting areas for a moon base since it's likely there is water ice there in deep craters, plus availability of continuous sunlight.
     
  19. Saghost

    Saghost Active Member

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    Something in excess of a third of the fuel in a typical launch is spent just overcoming atmospheric drag and gaining those first 90 miles.

    In principle, a somewhat longer version of the vacuum tower could be built at an angle - at which point it could supply some fraction of the final orbital velocity as well as the energy to get into orbital space in the first place.
     
  20. RDoc

    RDoc S85D

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    I'm still holding out for lunar uses of both beanstalks and rail guns. Less gravity and a vacuum ready made.
     

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