If you build a structure that is simultaneously light enough and rigid enough to stand up to atmospheric pressure, you could suck out all the air and make it float. Have we developed the engineering prowess to make something like this yet?
If not, how close are we and what are major engineering constraints that still limit us?
Long and sometimes contentious thread from 2016 on point: http://boards.straightdope.com/sdmb/showthread.php?t=802451
The short answer is it’s essentially impossible with real world materials. Including ones we haven’t invented yet. You need almost pure unobtanium to get something that rigid, strong, and light.
The key thing about an equal pressure balloon is the gas *pressure *inside is the same as outside. The difference in gas density is what makes the lift.
Going from that equilibrium to a vacuum-filled balloon you only gain lift equal to the weight of the gas you remove. But you lose the gas inside pushing out to hold the vessels shape. So now your structure needs to withstand all that pressure instead of zero pressure.
IOW, remove 10 lbs of helium, gain 10 lbs of lift, and install 100 tons of steel to hold it together. That way does not lie a successful balloon.
Nor is there much point. Helium is one seventh the weight of Nitrogen gas, so you’ve reduced the weight of the volume by 86% of the displaced air using Helium, so there is only 14% left to gain and only 7% if you use Hydrogen, not counting the weight of the enclosure and a balloon is going to be much lighter than a pressure vessel.
Except we’re running out of Helium but we have literally infinite supplies of vacuum.
The answers in that thread all seem to be talking about a completely hollow internal space which is a structurally difficult item to build. But there’s no requirement for the item to be hollow, adding internal reinforcement significantly decreases the weight.
I’m imagining something like aerogel wrapped in a thin, impermeable film. If aerogel can resist the crushing force of a person standing on it, it should also be able to resist atmospheric pressure.
Also, I’m not talking about economic practicality. I’m merely wondering if material science has advanced to the point where such a thing could be constructed as a proof of concept.
Has alpha radiation emmission by the rocks stopped ? I think it keeps on coming.
It might be more expensive in future when natural gas reserves are depleted. Then they have to go back to the old natural gas sites and extract the gas just to get helium.
By that logic, we’re not running out of coal, oil or natural gas either.
The supply of hydrogen is not infinite but may be second only to vacuum. I know there’s a safety issue there, but vacuum vessels have a very high risk of implosion and a tiny leak in one may be a greater risk than igniting hydrogen.
The key tradeoff is whether your aerogel+ vacuum mixture is more or less dense than helium. If more, you’re losing lifting performance not gaining it.
The cool thing about a gas is that if you’re OK with a non-rigid structure, AKA a balloon, the envelope plus the gas inside have near infinite pressure resilience for almost zero weight. Your balloon may dynamically smoosh in a wind gust or whatever, but it also dynamically smooshes back out. Try duplicating that trick with a semi-rigid material. It’s darn near exactly the formal definition of the difference between gas phase and solid phase.
The critical engineering point remains that compared to Earth atmosphere, helium already weighs very close to zero. There’s so little left to be gained by going to true zero that you can’t afford to spend more than a tiny fraction of that gain on getting there.
No, not even remotely. The problem isn’t one of material strength as it is geometry, i.e. such a rigid wall vessel would have to have extremely thin walls, and all thin-walled structures are sensitive to local buckling regardless of the tensile and shear strength. Filling it with a reinforcing material such as aerogel helps resist buckling but at the expense of additional weight, and even the lightest aerojels weight more than a low density gas.
Meanwhile, hot gas and inert low density atmosphere inflatables work just fine. If we were truly running out of helium (we aren’t as helium continues to be produced by decay processes, and will be a waste pruduct of deuterium-tritium fusion when we finally make that practical, but the United States foolishly decided to sell off the National Helium Reserve, so our standing reserves are depleated) we could simply design high temperature adibatic membranes and use very hot gas to produce an amount of lift per unit volume approaching that of vacuum. As LSLGuy notes the theoretical advantage of a rigid vacuum hull is so minimal there is little reason to expend effort on it even if it were physically practicable.
Stranger
We could cleverly build our rigid structure in the shape of a boat … we wouldn’t need to evacuate the air for it to float … I think we’ll find that if we put this matter to a vote … the odds of anything coming along will be quite remote …
Economical, useful, etc. is not the question. Can we make a structure that will float on Earth out of a material that will displace more enough water to float that if for spaces, would not. Correct??
The glass vacuum inserts on old style thermos bottles. Fill just that with water and will it still float?
Battle ships float and all it’s parts individually do not. The trick is to displace displace enough water I am thinking.
Now, to float in the air. What density of air? On a cold dry day of high pressure in a polar area at sea level with a double walled glass flask of some dimension that also can stand some internal partial vacuum is impossible? Artificially cold compressed air but not to a liquid state?
Steel drums with only a tiny amount of air are found floating below the surface of the water.
A glass thermos bottle will not be able to do that in some state of air which is compressible but is still air?
Proof of concept???
Nope, sorry. As above, any material you care to use is significantly heavier than any air that might be displaced by the construct, no matter what you build it from.
And the answer has already been given: We cannot. We already know the most efficient shape for something like this, and we can calculate the needed material strength for an enclosure of that shape, and the needed strength is beyond anything we can imagine actually making.
And as for the notion that "we’re running out Helium: Wired: “The Dire Helium Shortage? Vastly Inflated.”
We actually need helium more as a coolant and working fluid than for inflatables, and we have sufficient known and predicted reserves which exceed the expected needs for the foreseeable future, even if we start building helium-cooled fast fission reactors. (The helium cycle is closed so the need for each reactor is finite, and there are arguably better concepts for breeding fertile material into fissile fuel and burnup of actinides.) We don’t need to build rigid vacuum structures for a few percent improvement over low mass elemental gases.
Stranger
I’m perfectly happy to concede that vacuum buoyant structures are not and will never be economically practical as anything but a novelty.
Still, exactly how close are we to building them now? Are we any closer than we were 5, 10, or 50 years ago? Are there any promising areas of research that might yield one on the future if pursued far enough? Or does there exist some physical law that would make materials approaching the limit of what’s needed to build them theoretically impossible?
Well, post not in order but …
Now if you choose not to believe Chronos and others who have said pretty similar, fine, but why keep asking?
Seriously OP: read the thread I cited in post #2. For awhile it gets bogged down in the practical utility of blimps/dirigibles. But then on page 2 it gets fully back on track about vacuum vessels for flotation. There’s further refs to earlier threads. The thread spins in and out focus on this issue several times before it’s finally done.
But along the way real material & structural engineers provide calculations. A vacuum balloon needs gossamer weight with the compressive & bending strength of high end specialty steel.
Maybe someday when we can grow flawless single molecules of polymeric carbon crystal (graphene) the size of houses in whatever shape we want we’ll be able to pull it off. Maybe.
But right now it’s like asking how much closer we are to the first hyper-lightspeed starship than we were in the Space Shuttle era. To a first approximation the answer is: we’re not making progress at all. It’s utterly beyond our reach. So nobody’s really trying for that as such.
We cannot build rigid-wall structures that are light enough to be buoyant in sea-level atmosphere. I don’t know how many more ways to say this. It is not a matter of progressive development of tensile or shear strength of the materials; it is a result of the geometry of sufficiently thin-walled structures beng sensitive to local buckling regardless of material properties, and there is no material sufficiently light to resist compressive loads that would be lighter than air.
Stranger