h a l f b a k e r yContrary to popular belief
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Recently posted on this site was in adea for a "lite" space elevator, with a minimal superstructure buoyed up by balloons. Balloons cannot provide lift in very thin atmosphere, and so the area of the space elevator extending very high still needs a means of support.
I propose that the top of the
elevator be held in place by a solar powered perpetual rocket running on compressed air. Large solar panels capture the solar energy which is abundant at high altitude. This is used to run a pump which draws air up a tube running the length of the space elevator. At the top, this air is accellerated with great force into one or more rocket nozzles pointing down and away from the elevator. These nozzles could also be used to steer the top of the elevator to meet spacecraft etc as well as resist high winds lower down.
The problem with propulsion in space is that energy is available, but there is nothing to throw in the opposite direction. This approach makes use of the connection to earth to get something to throw.
Buoyant Space Elevator
http://www.halfbake..._20space_20elevator
A nifty idea. [bungston, Oct 05 2004, last modified Oct 17 2004]
Space Elevator
http://science.hows.../space-elevator.htm
From howstuffworks.com [st3f, Oct 05 2004, last modified Oct 17 2004]
[link]
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How could any amount of pumping draw the air up the tube, when there is already vacuum all around failing to draw up the rest of the atmosphere? Fundamental flaw, methinks. |
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(Now, it might work if you had pumps creating a high pressure in the tube at ground level. Someone else can do the math - there's always someone with a calculator.) |
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I suppose this is a space elevator, and the whole point is to move things up from the ground. However the question of whether the topside pump would work is interesting. I am not sure it would. |
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DrCurry is right, it will work only if the pump is on the ground. Also, why not put the solar power on the ground so the rocket has less to (perpetually) lift? the power loss through the atmosphere is small, and the arrays would be much cheaper. Also, the air could be heated electrically to give a better specific impulse to the rockets. |
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BUT what about the environmental impact? are we sure that this won't cause a lot of air to be lost to space? |
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Maybe you guys haven't read 'The Fountains of Paradise' by Arthur Clarke. The dynamics of the space elevator is clearly explained. It's afixed structure with a station at geostationary orbit and a counter weight past that. And yes, the problem is that it requires materials several orders of magnitude stronger than any we have under development. |
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That's what I like about Clarke: he only breaks ONE law of physics at a time. |
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The solar power station is weightless, in orbit. It is attached to the elevator by a tiny wafer thin wire. I put it up there because the suns rays pack more punch and you dont have to worry about dust, clouds etc. |
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Re: Mr Clarke. There's more than one way to skin a cat. |
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I'm afraid [DrCurry] is right. Suction works by creating a presure differential that is greater than the gravitational pull. The difference between a partial vacuum and more of a vacuum is unlikely to spirit up much air from ground level. |
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The geostationary orbit should be almost good enough to hold it in place. As for trimming, why not consider a different propellant medium, such as using an ion drive. The propellant could be shot up the lift and the energy stored at the top used to accelerate it. |
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//are we sure that this won't cause a lot of air to be lost to space?// |
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It's estimated that our atmosphere looses billions of cubic feet of air at the polar regions. Be we also recieve tons upon tons of raw material from space each day, like fragments from asteroids whos chemical composition includes oxygen. Or ice from comets which also includes oxygen. The earth is not a closed system. We don't have to worry about sucking the air off our planet any time within the next eon. |
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(What RusNash said) Build it according to the Arthur C Clarke's instructions and the whole thing's under tension anyway. I can't see the need for these downward pointing nozzles. |
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But then they'd point out to the sides, surely? |
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// There's more than one way to skin a cat. // |
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I know a dozen or so, but I'm always willing to learn ...... |
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The nozzles would point wherever you wanted. I envisioned mostly down, to keep the rest of the elevator from being pulled back to earth. But they could be adjusted to point sideways - which would be useful for bringing the top of the elevator to bear on the space station etc. |
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(+) Of course the real joke is the elevator itself. But this add-on idea is a good one. You want to use water, of course, not air -- no momentum with air. And you don’t want to use solar power -- there’s no way to support all those solar cells at the top -- it won’t be weightless, you know. So you install a nuclear plant at the bottom, and a string of pumps along the elevator to pump the stuff up. The weight of the pipe and pumps and electrical cable will be enormous, of course, much greater than what you’d get from ejecting the water...so eventually you’ll have to resort to vacuum balloons, disguising them as pumps... |
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//it won't be weightless, you know//
Er... it will at the orbital anchor. That's really the point of a space elevator. (link to howstuffworks). |
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Even if you could suck the air out of the tube from
space, you'd need a very stiff tube to not collapse
under the suction necessary to move that air
column, like sucking a straw in a really thick
milkshake, it would collapse. |
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And using positive pressure with pumps on the
ground, you've got to put a lot of force behind
that air column to push it out of the atmosphere
and into space. Air looses it's buoyancy once it's
out in space away from the surrounding air and it's
simply dead weight. The tube would need to be
able to stand up to that pressure. Keep in mind,
the gravity up there isn't absent. When you see
astronauts floating in orbit, it's because they're in
a perpetual "fall", where their velocity is acting
against the gravity, not because there's not any
gravity pulling on them. This tube and air column
would just be standing their getting pulled down.
It would be very very heavy. To get the force
pulling upwards that A.C. Clark theorized, you'd
need a heavy weight at the end to be out beyond
geosynchronous orbit which is really, really far out
there. |
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So by the time you've put all the structural
stiffness and associated weight into a tube that
could do such a job, the amount of air you could
push through it wouldn't do much to keep it
upright. |
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That being said, you could theoretically build a
structure going out into space. Question is
whether or not it would be worth it. |
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the altitude to which a gas may be pumped is limited by the pressure at which that gas liquefies. I haven't done the math but I suspect that your gas would need to be delivered at liquefying pressures especially should any reasonable rate of flow be expected. Sounds like a real challenge re. drag, size of tube and density. Suspect that the result is neg. sum. You might get by with a fuel/oxidizer setup but the atmospheric forces seem like a real tough sticking point (not to mention the weight of the tube itself, angels hair I presume. ) |
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Right WcW, I had actually looked into this with
pumping gaseous oxygen and fuel and even with
that there's no way. The static pressure you'd have
to overcome just to push the stuff through would
require a thick enough tube to make this un-
reasonable. |
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Even if you could do it you'd be burning so much
fuel to keep this tube upright it would be far less
efficient than just loading up a rocket with fuel
and a payload and being on your way NOT trailing a
200 mile long tube behind you. |
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I had also thought of having a tube filled with
hydrogen that a rocket would travel up, burning
the hydrogen as it went, but when you ran out of
atmosphere you'd run out of floating hydrogen
sock. I also considered a string of free floating
hydrogen
balloons being gobbled up Pacman style but again,
what's gained by doing that? |
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Like many neat ideas, the efficacy of the present
method has to be surpassed to make something
worth while and getting into space with a 60 foot
metal tube filled with fuel and oxidizer does the
job pretty well. |
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you are simply thinking too big. |
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If you want to build something in a desert - use the SAND |
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And rockets are like dinosaurs - big, loud and had to die out to make place for mamals |
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you'll do better to leave off the weight of the motors
and solar panels and pump the air from the ground. |
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