Space elevators?!?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by orcot, Mar 23, 2007.

  1. Fraggle Rocker Staff Member

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    Huh? The whole point is to make space travel cheaper. We won't need spacecraft that are sturdy enough to withstand takeoff and landing in Earth's gravity yet powerful enough to reach escape velocity from that gravity. Those spacecraft are enormously expensive. Most of their fuel is expended on moving the bulk of the craft itself rather than the passengers and other contents. With an elevator all you have to do is transport the people and goods to the top--which can be done very energy-efficiently by making sure you have a load coming down every time one goes up. Then you launch an absurdly flimsy spacecraft with a payload much larger than itself so your fuel is expended on doing real work instead of moving the ship back and forth.

    A space elevator is a very sensible idea. The only drawback is the possibility that some Religious Retards will find an excuse to blow it up, probably while there are ships out that will now have no way to get their crews back to earth.
     
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  3. Starthane Xyzth returns occasionally... Valued Senior Member

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    Plus the obvious "light pollution" aspect of having one or more gigantic, permanent towers stretching up to the height of geostationary satellites - let alone a solid, manmade ring encircling the Earth. Ground-based astronomers would absolutely HATE it.

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  5. Pete It's not rocket surgery Moderator

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    How much light do you expect it would produce, Starthane? And how visible do you think it would it be from 35000 km away?
    I don't see ground based astronomers complaining about light pollution from existing satellites.
     
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  7. Starthane Xyzth returns occasionally... Valued Senior Member

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    The top of a space elevator would have to act as a shipyard, a commercial spaceport - be a massive, fixed installation, an orbital city where thousands could live and work. What else would justify the expense of building the elevator? Something 25 miles across orbiting Earth at the same diatance as the Moon would shine like a 1st-magnitude star; this would be a lot closer.

    If the various space elevators did indeed give rise a full planetary ring, it would look thin but extremely bright, dominating the night sky. Even when in the Earth's shadow, its countless artificial lights would no doubt still be visible from the ground.

    What I was really thinking of, though, was the elevators themselves. Their lower portions, reaching down to the surface, would clearly be very prominent.

    But I assure you: personally, I'd consider the light pollution a very small price to pay for opening up the Solar System! If it can be safely and cleanly built some day, I'm all for it.

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  8. Janus58 Valued Senior Member

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    That depends on it's albedo. While it might be that bright if its albedo is the same as the moon's, it need not be that bright. I would expect that any surface that catches any large percentage of sunlight would be covered with photocells for energy production and would reflect very little.
    Besides that, 25 miles across seems a little excessive. You could put a population of 150,000 in a sphere just 2km across, without crowding them (1 person per every 8000 m^2)
    At night, when light pollution would be a problem, the lower 16,000 km of the elevators would be in the Earth's shadow.
    Besides that, just how much ground-based optical astronomy would still be done at this time?
     
    Last edited: May 30, 2007
  9. phlogistician Banned Banned

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    Well, since this would afford cheap launches of Hubble successors, I should think astronomers would be rather happy about it. Well, apart from the loss of trips to Mauna Kea for observations

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  10. Starthane Xyzth returns occasionally... Valued Senior Member

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    The Moon looks brilliant silver in our night sky, but it is actually a very dull, grey rock, reflecting only about 7% of incident sunlight. A metallic or even carbon-fibre structure might be more reflective than this.

    Ground-based observatories will always have a place, even if eventually they're only amateur. A lot of important discoveries (eg. comets) have been made by amateurs.
     
  11. orcot Valued Senior Member

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    The moon is 3000 km in diametre would any such a long structure be wider then 1 metre on average

    ... not for a very long long time ground baseobservatories are going to stay useful for a very long time
     
  12. CANGAS Registered Senior Member

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    But would you ever be able to provide rigorous calculated numbers to PROVE your suspicions?

    No way.
     
  13. CANGAS Registered Senior Member

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    At halfway, up and down cars stop by magicke, or, does power become used to stop motion of cars?
     
  14. CANGAS Registered Senior Member

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    In case you were asleep when you were reading my previous posts, 2inq., I will repete my opinion: THE CONCEPT OF AN ORBIT ELEVATOR CONTAINS A RAFT OF HUGE AND SEEMINGLY INSOLVABLE practical engineering problems.

    What part of my post: "practical engineering problems" is it that you are having the most trouble understanding?
     
  15. guthrie paradox generator Registered Senior Member

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    So you claim. I understand that many engineers disagree with you. However, not being personally aqainted with their work, I cannot demonstrate this to you.
     
  16. Pete It's not rocket surgery Moderator

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    Perhaps, if I chose to. I chose not to, which I why only I offered it as a suspicion.

    What do you think, CANGAS?
    And can you provide "rigorous calculated numbers" to support your thoughts?

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    Last edited: Jun 4, 2007
  17. Oli Heute der Enteteich... Registered Senior Member

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    Really? What would they be?
     
  18. Pete It's not rocket surgery Moderator

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    Definitely huge. Unsolvable? I wouldn't dare to guess.

    Materials,for one. Spinning enough carbon nanotube to make a 35000 km cable that might be tens of metres thick at the top is a tricky proposition.

    Power delivery, for another. Laser power? Superconductors? Both rife with difficulties.

    Managing traffic. Not just traffic up and down the cable, but also satellite traffic that will collide with the cable if not managed.

    Constructing a base tower.

    Disaster management, including earthquakes, thunderstorms, solar flares, and meteorites.

    Definitely huge, huge practical engineering problems. The Apollo program doesn't even come close.
     
  19. Oli Heute der Enteteich... Registered Senior Member

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    Huge, yes. Unsolvable, no.
    Not with money thrown at it.
    It's just bigger, not necessarily more difficult. Quantitive differences, not qualitative.
     
  20. Pete It's not rocket surgery Moderator

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    I'm not so sure. Maintenance is one thing that strikes me as quite different qualitatively. How do you maintain a 35000km cable under extremely high tension and under constant bombardment from solar wind and micrometeorites?

    This is not stuff that has been done before... it's not just scaling up existing tech. There are brand new problems to solve.
     
  21. Oli Heute der Enteteich... Registered Senior Member

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    Yeah new problems are the fun of engineering. I'm not sure solar wind would be one them though, haven't looked too closely at it other than one or two "back of the envelope" projects.
    I vaguely remember that the "high tension" is mostly due to the weight of the cable below. And that it reaches a maximum value and then tapers off as the cable approaches GSO altitude.
    IIRC Pournelle and Niven did some hard (ish) thinking on this, with calculations and suggestions. But I can't remember which book it was in. Damn.
     
  22. iceaura Valued Senior Member

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    A cable that long, if somehow (huge static electricity buildup, mishap?) it broke at about 30km, could potentially take out city buildings on the other side of the planet from its base.

    Pretty spectacular possibilities.
     
  23. Oli Heute der Enteteich... Registered Senior Member

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    In Kim Stanley Robinson's Mars Trilogy (Red, Green, Blue) someone snapped the cable during a civil war and wasted most of the domes and colonies that were in-line with its path as it fell.
    Doesn't bear thinking about.

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