Tunnel to space

[TommyThompson]

TL;DR 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.

 

[Ibix]

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.

 

[phinds]

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.

 

[Baluncore]

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.

 

[sophiecentaur]

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 .
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 . . . . . . . .!

 

[Filip Larsen]

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.

 

[TommyThompson]

The tube would be exposed to the vacuum of space at the top. Therefore it's a vacuum tube.

 

[Ibix]

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...

 

[phinds]

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.

 

[hmmm27]

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.

 

[Ibix]

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.

 

[phinds]

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.

 

[hmmm27]

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.

 

[Vanadium 50]

A "vacuum tube" is an electronics device.

Yes, but we can minaturize them with transistors. Then the tube is only 2 meters tall.

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.

 

[sophiecentaur]

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.

 

[StandardsGuy]

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.

 

[FinBurger]

The whole atmosphere is exposed to vacuum at the top. Yet somehow we continue to breathe...

I think you are not getting the joke.

 

[phinds]

I think you are not getting the joke.

What on Earth makes you think it was a joke?

 

[Ibix]

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.

 

[StandardsGuy]

Yes, but we can minaturize them with transistors. Then the tube is only 2 meters tall.

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.

 

[Al_]

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.

 

[Al_]

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

 

[russ_watters]

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]

 

[Filip Larsen]

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.

 

[Ibix]

[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.

 

[Janus]

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.

As air flows in the bottom, air builds up in the tube below the projectile. The weight of this air acts against the air flowing in. The pressure differential between air flowing in and air at the bottom of the tube becomes less and less until they equalize. This will happen when the weight of the projectile plus the weight of the air below it weighs the same as a column of just air of equal diameter to the tube.
90% of the atmosphere's weight is below 16 km of altitude.
So let's say that your tube is 1 meter in diameter, and your projectile masses 0.5 kg
in this case, at the very start, the upwards acceleration would be 10 m/sec/sec (~ 1g), but would die off to zero at ~16 km.
Now if the acceleration had remained 10 m/sec/sec over the same distance, the projectile would have reached ~ 0.566 km/sec or just small fraction of escape velocity. With a decreasing acceleration, you couldn't reach even a fraction of this.
Opening ports along the way would do nothing towards improving this.

 

[willem2]

So let's say that your tube is 1 meter in diameter, and your projectile masses 0.5 kg
in this case, at the very start, the upwards acceleration would be 10 m/sec/sec (~ 1g), but would die off to zero at ~16 km.
Now if the acceleration had remained 10 m/sec/sec over the same distance, the projectile would have reached ~ 0.566 km/sec or just small fraction of escape velocity. With a decreasing acceleration, you couldn't reach even a fraction of this.

I don't get this calculation. I think an air pressure of 10^5 Pa across pi/4 m^2 would give a force of 7.5*10^4 N producing an acceleration of 1.5*10^5 m/s^2 with a mass of 0.5 kg. I
I think the problem is in accelerating the mass of the air behind the projectile, which will be heavier than the projectile after only 0.5 meters of tube.

 

[Ragtrade]

Looks like this question has opened a big can of 'space' worms - or is it orbital frogs?

Anyway, as a PF 'newby', I thought I would add a couple more cans of worms to the fray:

Surely the issue here is: Can you lift a significant payload to, let's say, the edge of the atmosphere with far less 'cost' (energy?) than the current brute force 'Tsiolkovsky' technology? Well, since the the seventeenth century we've had people raising modest payloads very high into the atmosphere for little more than the cost of building a 'balloon' structure and a fair amount of hydrogen/helium/hot air ( plenty of that around this page methinks - Consider also, the Germans in the first World War used similar methods to Aerially transport fairly large payloads across Europe with a fairly primitive, if not ill conceived, version of said balloon technology. Additionally, Austrian skydiver Felix Baumgartner in 2012, rose to an altitude of approximately 39km in 2 1/2 hours in a 'balloon/capsule' before jumping off to freefall back to the ground! In terms of getting 'hardware' to that height it was not an insignificant weight: 1300+ kgs. Consider how much fuel, let alone the other resources and man hours involved in NASA's Mercury capsule 9 at 1400kgs consumed!.

So, let me pose a further question/suggestion: Would it not be possible to use a balloon system to at least get much of the required materials and personnel to the outer atmosphere to team up with Tsiolkovsky/Plasma/ other tech powered vehicles where the easy part of putting them into orbit for onward transfer to their chosen destination - and return the balloons to the ground safely for further 'missions'? has anyone (NASA?) done a costing on such a system? Such a system would involve no significant fuel costs. Gravity is doing the work for you!

So, NO vertical Musk style 'hypertube' required! (Q: what volume x pressure would be needed to be injected into a tube to launch a 'vehicle' up such a vertical Musk tube to propel it with positive pressure all the way to edge of space with velocity increasing all the way - Thus providing perhaps some momentum assitance to get it to orbit? A further thought: If you used Hydrogen or helium as the initial injected 'propellant' gas, how far up could the vehicle be propelled by the lifting force of the lighter than air gas. Clearly, the volume of injected 'gas' would need to be at least the same as the volume of air in the volume of atmosphere occupied by the tube itself, since the same gravitational forces wil be acting on the injected and enclosed gas - plus of course enought o counter the weight of the vehicle.

Another thought: If you fill the tube with hydrogen (yes it's rather a lot!~) at atmospheric pressure (reducing all the way up of course due to its own wieght) with a cap at the 'space' end and maybe caps at various heights to 'entrap' volumes of the lighter than air gas, would that not create a 'lifting' force against the caps thus helping support some of the weight of the structure?

So, using a lighter than air system could result in enormous savings (fuel etc) in getting a useful sized payload significantly towards the outer atmosphere or space since most of the weight of a rocket is the fuel it carries. Yes, of course a balloon system is slow (2 1/2 hours compared with 5 mins) but in terms of the overall time taken to get said payload into space, a few hours is neither here nor there.

Clearly there would be huge technical issues transferring the payload vehicle to another, normally orbit/space based vehicle for onward travel but I don't believe they are insurmountable. Just needs a new direction of technical development - What do you guys think?

 

[Ibix]

That's not far off the White Knight launch vehicle, which is a jet aircraft that lifts a smaller capsule (SpaceShipOne) to altitude. It was part of Burt Rutan's Scaled Composite effort for private lift to orbit - now owned by Virgin Galactic. I think the advantage to a jet over a balloon is that you can launch your space vehicle with a respectable speed in a controlled direction, whereas a balloon is slower and vulnerable to wind. That's less of an issue if you are coming down, but important if you intend to continue upwards.

 

[Filip Larsen]

Can you lift a significant payload to, let's say, the edge of the atmosphere with far less 'cost' (energy?) than the current brute force 'Tsiolkovsky' technology

Keep in mind that the majority of the orbital energy in low Earth orbit is kinetic and not potential so any launch from the surface of Earth has to use most of its energy release to accelerate the payload rather than lifting it higher. This also means that the main reason to increase the altitude of a payload with aero-static (balloon) or aero-dynamic (airplane) before any rocket stage take over is to get to less denser air so the needed orbital speeds can be obtained by the rocket with less losses to aerodynamic drag.

Also, its not only about reducing energy. Simplicity and scalability are two other aspects that goes a long way to make a launch system feasible, both of which suffers if you try to pre-lift your payload to less dense air. As it is, even moving the launch system to a high mountain is apparently not worth it if you consider where all the major launch sites are actually located.

 

[nasu]

, accelerating the projectile to high speed.

High speed? What makes you say that? The force exerted by atmospheric pressure on the bottom of the projectile may be less than the weight of the projectile. In which case the velocity will be zero. All this to obtain a pressure on the bottom of one atmosphere? Vacuum does not have some magic power. It does not create large forces on objects. At the most it can allow the atmospheric pressure to act unbalanced.

 

[Captnq]

Well, wait a minute... So, what if we built a giant Funnel? This funnel is transparent. We make the base about a mile wide and coat the ground beneath it with Fanta Black. That is going to generate a great deal of heat when the sun hits it. The hot air will rise, getting trapped in the funnel. This will create a constant upward thrust. Depending on how high we could get the funnel, a great deal of air will be rushing up it. If your spacecraft is carried up by a balloon it'll be forced out the top with a considerable amount of force. I bet you could get quite high up into the upper atmosphere with this set up by late afternoon, especially if you set it up in an area with extreme temperature swings and no clouds. Once the balloon passes the end of the tube, your craft cuts loose, activates thrusters, and takes the rest of the way into low orbit.

 

[sophiecentaur]

@Captnq just do a few sums about the energy required to lift an object to a great height. The thermal Power from the Sun, warming a piece of ground is limited to about 1kW per metre square. You are actually proposing what, in general terms, is called a Heat Engine. They are not a very efficient way of using heat, when the temperature difference is small so you would get a small fraction of that thermal energy that arrives at the ground.
What is being proposed is an Engineering Project and, in Engineering, the numbers really do count, I'm afraid. Solar energy is certainly handy but it needs to be 'concentrated' into a fuel or some other form before it's able to provide any serious amount of intense mechanical work. Take a look at the 'special cases' of solar driven aeroplanes and boats to get an idea of its limitations.

 

[Ibix]

The basic principle of the device to which you refer, captnq, is called a "solar chimney" if you want to look it up.

 

[sophiecentaur]

The basic principle is called a "solar chimney"

It's the sort of effect that drives the weather; massive amounts of energy involved but not particularly usefully directed when the energy turns up in a small space. (Hurricanes and other bad weather examples). Wind turbines and sailing ships use it but don't have much effect on (even) the local weather.