I Is it possible to use the vacuum to launch a rocket?

[Peanut Butter Space]

Hey I'm new to Physics. I have a question. Is it possible to use the force generated when air entera a vacuum tube to launch something into space? Can anybody throw some light on this in simple words please. Thank You.

 

[anorlunda]

You have to start thinking about the kinds of forces or energies, and the magnitude (size) of those forces or energies.

Yes, if you have a cylinder with a vacuum and a piston, air pressure will push the piston in. You can use that to generate power, and you can use the power to do useful things including lifting them.

But to get something into space? It depends on the size of the vacuum cylinder and the size (mass) of the object, and the starting place. For example, NASA has a Pegasus rocket that it launched from an airplane flying as high as it can. That takes much less energy than launching it from the ground. All those things determine the magnitude and your question does not specify those things. It takes a certain amount of energy to lauch a certain object, but it doesn't matter where the energy came from.

On Physics Forums, the better the quality of the question you ask, the better the quality of the answer.

 

[Peanut Butter Space]

You have to start thinking about the kinds of forces or energies, and the magnitude (size) of those forces or energies.

Yes, if you have a cylinder with a vacuum and a piston, air pressure will push the piston in. You can use that to generate power, and you can use the power to do useful things including lifting them.

But to get something into space? It depends on the size of the vacuum cylinder and the size (mass) of the object, and the starting place. For example, NASA has a Pegasus rocket that it launched from an airplane flying as high as it can. That takes much less energy than launching it from the ground. All those things determine the magnitude and your question does not specify those things. It takes a certain amount of energy to lauch a certain object, but it doesn't matter where the energy came from.

On Physics Forums, the better the quality of the question you ask, the better the quality of the answer.

So it IS possible to provide the initial thrust for a rocket using a huge vacuum cylinder. Isn't it?
P.S. Sorry I am not very well versed in physics but I'm curious to learn

 

[anorlunda]

So it IS possible to provide the initial thrust for a rocket using a huge vacuum cylinder. Isn't it?

In theory yes. In practice no.

You used the word huge, but how big is that? You didn't specify the size of the rocket. If you want to start learning physics, use numbers rather than words like huge.

By the way, you can get energy from a cylinder that has higher pressure than the air (compressed air), or lower pressure than the air (vacuum). The physics is the same.

 

[ZapperZ]

So it IS possible to provide the initial thrust for a rocket using a huge vacuum cylinder. Isn't it?
P.S. Sorry I am not very well versed in physics but I'm curious to learn

So, the thing about physics is that it isn't sufficient to just say "what goes up, must come down". You must also say "when and where it comes down".

What this means is that it isn't sufficient to simply say "it is possible". There's a different between saying something is possible versus something that is (i) realistic (ii) likely (iii) economically feasible, and (iv) rational. There is nothing mathematically to prevent launching a rocket the way you describe, but why would someone want to do that over other means? This is where one has to present NUMBERS, i.e. this is the type of force that has to apply on a typical rocket with a certain mass, this is the amount of pressure one must provide, this is the compressor one than needs based on the previous two criteria, etc... etc. Real world works not only based on what is "possible", but also on what is feasible, and that last part depends on many other external criteria.

We often get asked here if it is possible for something highly unlikely to occur. Do you know that if you have a vase that has been broken into a thousand pieces, that according to physics, it is still "possible" that if you throw those pieces onto the follow, it can reassemble itself back into the original vase? The probably of that happening isn't zero, according to physics. But that probability is also unbelievably small, so small that it is unlikely to occur. After all, have you seen such a thing happening?

It means that isn't sufficient simply to ask "is it possible?" or to claim that something is "possible". Such a thing is useless if the likelihood of it occurring is ridiculously small, that it might as well not happen.

Physics, and science in general, involves both qualitative (descriptive) and quantitative (values and numbers) aspects. This is a valuable lesson to learn.

Zz.

 

[OmCheeto]

Hey I'm new to Physics. I have a question. Is it possible to use the force generated when air entera a vacuum tube to launch something into space? Can anybody throw some light on this in simple words please. Thank You.

Fun maths problem! But it looks as though others have figured out the answer: Yes.

ps. I worked out some very preliminary numbers, based on an ISS resupply ships specs(mass and diameter).

Initial acceleration: 160 m/s^2
Atmospheric pressure at the peak of Mt Everest: ≈1/3, as compared to sea level, which yielded an acceleration value of only 47 m/s^2​

And that's where I stopped, as, it's lunchtime.

 

[sophiecentaur]

By the way, you can get energy from a cylinder that has higher pressure than the air (compressed air), or lower pressure than the air (vacuum). The physics is the same.

Yebbut the maximum pressure difference you can produce with 'suck' will be One Atmosphere. With 'blow' there is not theoretical limit. Makers of the first steam engines couldn't make cylinders that would withstand positive internal pressures (they burst) so those engines worked by reducing the pressure inside a cylinder and allowing atmospheric pressure to push a piston in. Any half decent engine these days uses a positive cylinder pressure and it is far more powerful and efficient. A diesel engine may have a compression ratio of 20:1.
What would be the point of trying to drive a space launch vehicle by negative pressure, however you did it? (ZapperZ used almost the same words, I see)

 

[SirCurmudgeon]

This has been considered but not built (to my knowledge).
Here's a simple disign and calculation I ran out some time ago. See what you think.

http://www.thermospokenhere.com/wp/03_tsh/C7000___vacuum_launch/vacuum_launch.html

JP

 

[SirCurmudgeon]

Hi,

I forgot to mention that the "vacuum launch" makes a nice HS experiment. See
the an apparatus sketch at the bottom of:
http://www.thermospokenhere.com/wp/03_tsh/C7000___vacuum_launch/vacuum_launch.html

JP

 

[slow]

Hi. Leaving aside the calculations of the necessary energy, we must see a technical difference. A vacuum based thrower will provide all the energy in a short time, as the pool cue provides the ball with all the energy in the milliseconds that the hit lasts. The blow does not give an opportunity to correct something along the way. A rocket provides the energy gradually and makes it possible to guide the ascent of the ship in real time.

 

[OmCheeto]

This has been considered but not built (to my knowledge).
Here's a simple disign and calculation I ran out some time ago. See what you think.

http://www.thermospokenhere.com/wp/03_tsh/C7000___vacuum_launch/vacuum_launch.html

JP

One problem, off the top of my head, as that's a lot of maths, is that your final velocity of 231 m/s is a bit too low.
Google tells me that Earth's escape velocity is 11,200 m/s.

I think you need to add some above ground tubing.
Not sure how much, as pressure changes with altitude: atmospheric pressure = e^{(−0.0001436 * altitude + 11.506)}
and I'm really bad at maths.

ps. I got 244 m/s as a final velocity, based on your parameters, so I'm guessing your maths is correct.

4 meter diameter
22,500 kg projectile​

pps. A 775 meter deep hole only threw off atmospheric pressure by 10%, so I ignored that.

 

[SirCurmudgeon]

Thanks for looking...
Stage is not for "Escape Velocity," just less fuel.

Thanks, JP

 

[CWatters]

Just for info...

Early steam engines used the "vacuum" created when steam in the cylinder condensed. It was soon realized that this limited the performance of the engine.

 

[sophiecentaur]

Thanks for looking...
Stage is not for "Escape Velocity," just less fuel.

Thanks, JP

Can you be sure about “less fuel”? The ‘atmospheric engine’ was certainly not very efficient.

 

[OmCheeto]

Can you be sure about “less fuel”? The ‘atmospheric engine’ was certainly not very efficient.

My guess is "yes", as it's fuel that doesn't have to be lifted.

But, as ZZ said;

...but also on what is feasible...

I really need to solve this problem, as it looks quite fun.

ps. The Rooskies spent a WHOLE LOT of money digging a hole a while back. 12,000 meters according to google. From my calculations, the atmospheric pressure at the bottom of their hole is ≈5 times greater than at sea level. I'm wondering if "cube-sats" would melt at such as yet unverified accelerations: 85 g's ?