h a l f b a k e r yRecalculations place it at 0.4999.
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Jim has been pondering vacuums recently and figures he can reduce the fuel required to launch something into space by using another vacuum.
Take your favourite launch platform and stick a vacuum tube over it all the way up to the upper atmosphere.
...
Vacuum
Vacuum_20Maglev_20Accelerator
Right next door in this category! [bungston, Nov 20 2009]
Steam Space Launch
Steam_20Space_20Launch_20Facility
this is my favorite of the big vacuum launchers on the HB [bungston, Nov 20 2009]
DIPS
The_20Denver_20Inte..._20Peaple_20Shooter
The Peaple Shooter is also an evacuated tube but folks hopefully stay out of orbit. [bungston, Nov 20 2009]
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I am undecided as to weather to add specific equipment to evaculate the tube or to simply allow the launch vehicle heat to create a partial vacuum. |
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Without any special evacuation equipment the heat produced by successive launch vehicles will be retained by the enclosed atmosphere --- and the tube must eventually attain a partial vacuum simply because it is so tall. |
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Let's skip the whole problem of building anything that tall, which has been done to death in a whole load of space-elevator-carbon-nanotube dicussions. Let's also skip the fact that Jim is a bit of a pillock and annoys me. |
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One problem with the elevator is how to power the thing that climbs up it - which is why NASA just gave a whole heap of prize money to some guys who built a prototype tether climber that was powered by gound based IR laser. This system also gets around that problem by keeping the fuel on the ground. Just build the tube, pump out the air from under the platform, then let air in underneath the platform to lift it. |
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Quite a nice solution, except that instead of building an impossible thin rope into space, you now have to build an impossible large pipe. |
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[+/-] (If I understand Jim's idea correctly, which is far from certain) |
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Again with the poorly-done corruption of old, old concepts. I am going to start just auto-boning all the madness of this [madness] person. |
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Yes, a vacuum tube would save some fuel, OBVIOUSLY, but building it is a bugger, and firing a rocket up it would be a bad, bad idea. |
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This concept is not new, and is taken for granted, even. We, here on the HB, have several times discussed ways and means of keeping the open end of a linear accelerator's vacuum tube from filling with air. (-) |
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//I have several times discussed ways and means of keeping the open end of a linear accelerator's vacuum tube from filling with air// |
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Auto bone away --- but obviously there is no need for any such discussion here ("since the tube is so tall"). |
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This is a basic temperature/pressure/volume relationship --- raise the temperature of a liquid in a glass and it will boil out over the top. |
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In this case the 'glass' is a tube that opens to a natural vacuum, when the temperature inside the tube drops a vacuum will form. |
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Pretty sure there is an upper limit to the purity of vacuum this would create, determined by the temperature at which the tube reaches equilibrium. |
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Each craft up the tube would also carry out some air, volume determined by the closeness of fit between the craft and tube. The extra energy required to do this, however, would be similar to the energy used to pump out the tube from the bottom. |
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[Wags] Pretty sure the idea is just to use an evacuated tube to negate air resistance. |
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Jim, two basic problems. The first is common to all space elevator type structures. What are you going to build it out of. A structure at least 1 Megameter tall is not going to be buildable with any material available today, or in the forseeable future (long carbon nanotubes may be that strong under tension, but not in compression). |
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Second, how are you going to keep it from filling back up. 1 Megameter is considered the nominal upper edge of the atmosphere, but there are at least traces of stuff considerably beyond that. If you open up a huge hole, those traces will flow in and fill up your tube. An addition, in-gassing would occur, filling the tube from another source. |
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I believe you all misunderstand his concept..... |
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The idea he was proposing was to create a tube like the ones at the bank where the air rushing into the tube from the bottom towards the vacuum of space would propel the spacecraft INSTEAD of using fuel. |
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However that wont work either because first off, if you had a sealed tube 60 miles long going into low earth orbit, it would not evacuate because just like the atmosphere we have, gravity would keep the mass of air in the tube, even if you spent a week sucking out all the air the force of air under the craft would diminish every mile until there was almost no discernable pressure for propulsion before you reached the top. |
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//Take your favourite launch platform and stick a vacuum tube over it all the way up to the upper atmosphere.// |
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Works fine if your favorite platform is the moon. Otherwise, you'll have this inverted, J-type structure (assuming you want to achieve an orbit), with gases escaping around the rocket and filling up the tube before it ever gets going. What you need is a Jules Verne moon gun, but very tall. And no need to go all the way up, as a valve at the top could open at the last possible moment. |
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The Halfbakery community is not recommended for use as a surrogate brain. |
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I also suggest that you let your curiosity lead you to make more effort to figure out the science on your own before posting. |
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You're anonymous; no need to hide your confusion behind a façade of apathy. |
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Are you calling him apathy? |
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