OK we know that due to air pressure a vacuum balloon would not be possible on earth.
But would it be possible to create one that floated near space with almost no air pressure?
If so how much could it lift? what are its limits?
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$\begingroup$ What is going to hold it inflated? $\endgroup$– jkavalikMay 16, 2017 at 5:39
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$\begingroup$ The hull of the vacuum balloon could be lighter if the air pressure is lower, but also the lift force of the balloon is lower. You could not win this way. $\endgroup$– UweMay 16, 2017 at 8:36
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$\begingroup$ For near-space balloon flights, people use very large, light balloons that are filled only partially. As the balloon ascend, it expands. $\endgroup$– HobbesMay 16, 2017 at 11:19
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$\begingroup$ @Uwe Dang it. that's what I was afraid of. thanks anyways. $\endgroup$– HashbrownsMay 16, 2017 at 15:32
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5 Answers
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But would it be possible to create one that floated near space with almost no air pressure?
Possibly, depending on what material(s) you use to make the balloon.
If so how much could it lift? what are its limits?
That depends entirely on how big the balloon is and what material you use to create it.
A regular balloon uses internal gas pressure (typically helium or hot air) to hold its shape. A vacuum balloon would require a rigid shell (like a giant Ping-Pong ball) instead.
Since "almost no air pressure" is not the same as "no air pressure", you will need some rigidity.
Remember that balloons and boats float because they weigh less than the equivalent "medium" (air for balloons or water for boats) that they displace.
If you have 1 solid cubic meter of something, it'll float only as long as it weighs less than 1 cubic meter of air at that location (considering temp & pressure).
The problem is that the higher you go, the less that cubic meter of air weighs.
My guess is that you won't be able to find a material strong enough to hold its shape against the "almost no air pressure" but still light enough to weigh less than the amount of air it's displacing.
I'd like to be wrong though - vacuum balloons sound pretty cool.
For more info, see the Wikipedia page on Vacuum airships (lots of math there)
answered May 16, 2017 at 13:58
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The problem with coming up with an answer based on dimensional analysis is that you are asking about a balloon with an internal pressure lower than the external pressure, and the failure modes include leaking which is a materials issue, and buckling with is a complicated mechanical engineering problem. Neither of these lend themselves to simple and yet realistic models that could make an answer to this question easy.
As pointed out in this answer, on page 4 of NASA Technical Note TND-1366 The Orbital Behavior of the Echo I Satellite and its Rocket Casing During the First 500 Days (June, 1962) says:
PHYSICAL CHARACTERISTICS
Echo I has an effective cross-sectional area of 7,854 square feet. The launch weight of 157 pounds decreased to 124 pounds with the loss of 33 pounds of benzoic acid and anthraquinone which were used to maintain inflation for the first few weeks in orbit. Thus, the initial ratio of the weight to mean drag area for Echo I was 0.020 pound per square foot and reduced to 0.016 pound per square foot after several weeks in orbit.
Echo-1 was about 100 feet in diameter, so that change in weight of 0.004 pound per square foot of drag area corresponds to the 35 pounds mentioned. So we can assume that the balloon was inflated with 35 kg of gas.
So with a radius of 15.2 meters that's 58 kg in 14,600 cubic meters (after the gas leaked out), or a density of 0.004 kg/m^3 which is roughly 0.32% of a standard atmosphere.
I'm trying to find out more with What gas was produced in orbit from 33 pounds of benzoic acid and anthraquinone?.
What altitude does that correspond to? A ballpark scale height of 8 km gives 46 kilometers. The 1976 NASA Standard Atmosphere gives about 40 kilometer.
NASA Science balloons like this one typically go to about 30 to 35 kilometers.
So you could try to make a balloon like Echo I and go to about 40 kilometers but you could not use the trick of making it rigid as the gas leaked out since you'd be in the atmosphere. The balloon would start to shrink and drop in altitude as soon as the gas started to leak.
Helium balloons have already gone past 50 km according to https://en.wikipedia.org/wiki/High-altitude_balloon
Here is one popping at only 33 km
below x2: cropped and full size from Echo, NASA's First Communications Satellite
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OK we know that due to air pressure a vacuum balloon would not be possible on earth.
No, we don't know that. See, e.g., our recent paper Vacuum balloon - a 350-year-old dream, where we show that an evacuated sandwich spherical shell with ceramic face sheets and aluminum honeycomb core can be both light enough to float in air and strong enough to withstand atmospheric pressure. See also references to other work in this area.
As for a "near-space" vacuum balloon, I agree with @Uwe's comment: it is more difficult to build such a balloon as the mass of displaced air is very small.
Abstract:
The centuries-old idea of a lighter-than-air vacuum balloon has not materialized yet as such structure needs to be both light enough to float in the air and strong enough to withstand atmospheric pressure. We propose a design of a rigid spherical sandwich shell and demonstrate that it can satisfy these stringent conditions with commercially available materials, such as boron carbide ceramics and aluminum alloy honeycombs. A finite element analysis was employed to demonstrate that buckling can be prevented in such a structure. Other modes of failure were evaluated. Approaches to manufacturing are discussed briefly.
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$\begingroup$ The paper is really interesting, excellent contribution! I've added in the abstract to encourage readers to take the time to go read the whole thing.
+1$\endgroup$– uhohMar 20, 2019 at 2:39
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At 50000 feet the pressure is 1 psi or close there should be plenty of materials strong and light enough to with stand the forces. Use a traditional Balloon to lift the vacuum Ballon. Floating islands in the sky.
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$\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$– Community BotNov 8, 2022 at 11:30
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1$\begingroup$ Yes, but what is the pressure in the balloon & what is the bursting strength of the material the balloon would be made of? The pressure experienced by the balloon material = pressure inside the balloon minus the atmospheric pressure. The higher the balloon goes the smaller the atmospheric (external) pressure, the more the balloon expands & eventually ... BANG! $\endgroup$– FredNov 8, 2022 at 11:41
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Who says it is not possible on earth due to air pressure? Just because no one has done it yet? Theoretically, vacuum has 18% more lift then our strongest lighter then air gas. Obviously just a matter of finding the right geometry and metal. The way i see it nothing is truly impossible with enough dedication.
https://gfycat.com/queasycautiouscats
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4$\begingroup$ We say it is impossible because there is no material strong enough to withstand 1 kg/cm^2 of pressure while being light enough to be lifted by buoyancy. We also know the best possible geometry is a sphere, not a pentagon. That's the nice thing about sciences like physics: we've built really good models for physical processes so we can often calculate what will happen without having to do lots of experiments. $\endgroup$– HobbesMar 18, 2019 at 8:31
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2$\begingroup$ A balloon "filled" with vacuum would have no lift in a vacuum. No one has to try that one out to see if it works. $\endgroup$ Mar 18, 2019 at 12:57
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$\begingroup$ uh except its not 1kg/cm^2 on my icosphere is it? =) This is why a sphere is not the strongest geometric shape. Explosion happens from the points, Implosion happens at the faces. If you reinforce the center of each face against implosion, you had better believe that it will be extremely crush resistant. What is occurring is that the force is pooling to the center of each face, while the internal structure is reinforcing each face. gfycat.com/queasycautiouscats $\endgroup$ Mar 28, 2019 at 13:04
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$\begingroup$ Trust me, the physics is sound in vector potential. =) $\endgroup$ Mar 28, 2019 at 13:11