Tunnel to space

  • #1

Summary:

Build a tube to space.
Use our atmosphere to push a ship up the tube.
Build a tube to space.
Use our atmosphere to push a ship up the tube.
 

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  • #2
Ibix
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Amusing idea, but you can't lift a ship to the top of the atmosphere this way for more or less the same reason that boats float in water rather than sitting on the surface. And the atmosphere is so much less dense than water that you need a huge diameter tube to carry a small payload. If we had the materials science knowledge to build a tube strong enough to keep atmospheric pressure out while being big enough to contain a useful payload and being 20km tall, all without collapsing under its own weight, it'd be cheaper and easier to build a space elevator instead.
 
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  • #3
phinds
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Build a tube to space.
Use our atmosphere to push a ship up the tube.
Tommy, thinking outside the box is a great idea but only after you know what is IN the box. I suggest you study some basic physics.
 
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  • #4
Baluncore
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Build a tube to space.
Use our atmosphere to push a ship up the tube.
Welcome to PF.

https://en.wikipedia.org/wiki/Atmosphere_of_Earth#Pressure_and_thickness

Atmospheric pressure at sea level is due to the weight of all the atmosphere above. As you rise, the pressure falls, so it passes 1% of sea level pressure at about 20 km. It would require more pressure than 1% of sea level to lift a vessel. The pressure at the bottom of the tube would then be very high, due to the column of compressed air and the weight of the vessel.

Once the vessel was released from the top of the tube, the compressed air would escape and release all the energy you put into compressing it.
 
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  • #5
sophiecentaur
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Summary:: Build a tube to space.
Use our atmosphere to push a ship up the tube.

Build a tube to space.
Always worth a try, Tommy :smile:.
There are two issues here. Firstly, if the tube were to have a piston inside it, of sufficient area, then there could , in fact be enough Force to lift your ship. Force = Pressure times area. The pressure would be very low so the area would need to be enormous. That would mean you would need to extract (with a huge pump)all the air from above the piston.
You could (and they do) easily achieve the equivalent in water (Consider what happens in a Dry Dock which is pumped dry and then a ship floats up easily when water flows back in). So you 'could' lift a massive load but the density of Air (particularly the bit near the top of the tube) makes it just not practical.

The other issue is the same as for the often proposed 'space elevator'. It involves a line which tethers a large satellite in geosynchronous orbit. Cars could move up and down the 'rope', carrying people and materials up there with very little fuel involved. The problem with this idea is the sheer extent of the construction PLUS the fact that it would have to be mounted on the Equator and every plane (And satellite) would need to avoid it. Planes, maybe but there are thousands of satellites in lower orbits, some of which are not controlled at all. Just one collision . . . . . . . .!
 
  • #6
Filip Larsen
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Granted its a cute idea.

That would mean you would need to extract (with a huge pump)all the air from above the piston.
This also implies that the payload cannot gain more mechanical energy than the energy needed to pump the tube empty. If pumping has to occur at a decent rate, this implies a significant loss due to heat loss and similar.

And besides, if you have the capability to build a tube (with a piston-like platform to lift the payload) that can stand tall all the way to, say, 100 km while being both full and empty of air, then you may as well settle for a just tube filled with normal atmosphere where the platform is lifted by mechanical means instead (e.g. electric motors in the platform driving a gear-drive).

And thirdly, since orbital energy is mostly kinetic (and not potential), you still need a way to accelerate a payload away from the vertical whether payload is driven by air or other mechanical means. If this acceleration has to be done "by the tube" then it is has to curve approximately (I assume) in a parabolic shape relative to the flat surface of the Earth (elliptical relative to curving Earth). Alternatively the tube could just be used to get to some altitude from where you could launch horizontal, but then you may as well just go with the much simpler solution of using an airplane or similar to lift the payload with a booster, which is already in use.
 
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  • #7
The tube would be exposed to the vacuum of space at the top. Therefore it's a vacuum tube.
 
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  • #8
Ibix
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The tube would be exposed to the vacuum of space at the top. Therefore it's a vacuum tube.
The whole atmosphere is exposed to vacuum at the top. Yet somehow we continue to breathe...
 
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  • #9
phinds
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The tube would be exposed to the vacuum of space at the top. Therefore it's a vacuum tube.
Clearly you misunderstand what "vacuum tube" means. I say again, you would do well to just read some basic physics. Asking random questions on an Internet forum when you don't understand the basics is not going to prove very helpful.
 
  • #10
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The tube would be exposed to the vacuum of space at the top. Therefore it's a vacuum tube.
Not if the air is flowing fast enough... which is what you're going to need to push the wall up and keep it from falling over. Wind will mess it up.
 
  • #11
Ibix
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The tube would be exposed to the vacuum of space at the top. Therefore it's a vacuum tube.
To expand a bit on my previous, if you open a hole in the side of a spaceship, air will indeed rush out and leave the ship evacuated. Earth's atmosphere does not rush off because it's held down by gravity. Gravity will not stop holding down a bit of air just because you put a tube around it. So the tube will remain full of air.
 
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  • #12
phinds
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Not if the air is flowing fast enough... which is what you're going to need to push the wall up and keep it from falling over. Wind will mess it up.
What in the world does the air speed do with whether or not it's a vacuum tube? I think perhaps you also don't understand what a vacuum tube is.
 
  • #13
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What in the world does the air speed do with whether or not it's a vacuum tube? I think perhaps you also don't understand what a vacuum tube is.
Well... if you can keep the air flowing through fast enough it will be an evacuating - not evacuated - tube. A "vacuum tube" is an electronics device.
 
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  • #14
Vanadium 50
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A "vacuum tube" is an electronics device.
Yes, but we can minaturize them with transistors. Then the tube is only 2 meters tall. :wink:

It's still not 100% clear to me how this is supposed to work. It seems that the idea is to pump down the tube and open it up from the bottom and let the air rush in, pushing the rocket up as it refills the tube. If so, there are two problems with that:
a) compare atmospheric pressure to a Saturn V's thrust per area of the 1st stage.
b) even if this got the rocket to the top - which it wouldn't - it has no horizontal velocity and would just fall back again.
 
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  • #15
sophiecentaur
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If pumping has to occur at a decent rate, this implies a significant loss due to heat loss and similar.
HAHA - plus many other objections. The poor OP has stepped into a big pile of PF brown stuff with his fanciful idea. He has received a vast amount of theoretical and practical objections to it - but it's a topic that has so many different facets to it.

It's always 'the numbers' that count in schemes for getting away from Earth. We'll be using rockets for a good few decades yet.
 
  • #16
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Summary:: Build a tube to space.
Use our atmosphere to push a ship up the tube.

Build a tube to space.
Use our atmosphere to push a ship up the tube.
Good idea. After you get that done, build a Dyson sphere.
 
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  • #17
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The whole atmosphere is exposed to vacuum at the top. Yet somehow we continue to breathe...
I think you are not getting the joke.
 
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  • #18
phinds
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I think you are not getting the joke.
What on Earth makes you think it was a joke?
 
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  • #19
Ibix
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I think you are not getting the joke.
What makes you think this is a joke? It's far from the most harebrained misapplication of a misunderstanding of pressure that I've seen.
 
  • #20
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Yes, but we can minaturize them with transistors. Then the tube is only 2 meters tall. :wink:

It's still not 100% clear to me how this is supposed to work. It seems that the idea is to pump down the tube and open it up from the bottom and let the air rush in, pushing the rocket up as it refills the tube. If so, there are two problems with that:
a) compare atmospheric pressure to a Saturn V's thrust per area of the 1st stage.
b) even if this got the rocket to the top - which it wouldn't - it has no horizontal velocity and would just fall back again.
Shhh. You're giving him too many ideas. He needs to invent the thing himself. Maybe he wants to ride up on a cathode ray.
 
  • #21
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Hmm. Maybe, this isn't such a crazy idea, if....
Bear with me.
The tube slopes upward and ends at a high altitude where the air poses little frictional resistance, say 10km. There is a cover over the top end preventing the thin air entering. At ground level, it is also sealed by a door, and large pumps remove 99.9% of the air. Inside the bottom end is a
sharp-nosed projectile. When the air is pumped out, the door is opened. The tube acts as a gas gun, accelerating the projectile to high speed. Open the cover at the top just in time.
The Hypertube idea shows us that a sharp-nosed vehicle can avoid contact with the sides of a tube at hypersonic velocities in very thin gas.
The question is, can it reach orbital velocity. There are ways to boost the thrust, such as opening ports in the sides as the projectile passes, or using hydrogen gas like they do in gas guns. Hydrogen would achieve a higher pressure at the top, being lighter.
 
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  • #22
Al_
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a) compare atmospheric pressure to a Saturn V's thrust per area of the 1st stage.
yes, but that was lifting a much larger mass, and it was fighting air pressure in front of the rocket, and it throttled back part way through to avoid too much friction
 
  • #23
russ_watters
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yes, but that was lifting a much larger mass, and it was fighting air pressure in front of the rocket, and it throttled back part way through to avoid too much friction
You can do some basic calculations to see if this will work. You should know roughly how fast a rocket needs to go to achieve orbit, and you can calculate the acceleration based on the length of the barrel. Calculate the acceleration over a 10km barrel, then calculate the allowable mass per unit area. I suspect you will find the thrust woefully insufficient.

You could also compare to some proposed air-gun style launchers. They use enormous air (hydrogen gas) pressures.

[this assumes you could achieve a constant acceleration profile from 0 to mach 20+, with air rushing into the barrel]
 
  • #24
Filip Larsen
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this assumes you could achieve a constant acceleration profile from 0 to mach 20+, with air rushing into the barrel
And speaking of speed, its hard to see any projectile being propelled only by atmospheric air at STP to exceed mach 1.0. Even if mach 1 could be achieved all the way to altitude (which it can't) its still around 24 times too slow for low Earth orbit.
 
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  • #25
Ibix
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[this assumes you could achieve a constant acceleration profile from 0 to mach 20+, with air rushing into the barrel]
It's not going to rush in faster than the RMS velocity of atoms at sea level, is it? So the maximum attainable speed is going to be on the order of 300m/s. Optimistically. And you'd presumably stop accelerating around the height where the capsule weight equals the weight of air that would naturally be in the column above you. That'll be quite a lot before the top.

Not to mention the point that we don't have the materials to build 20km high towers.
 

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