What would it take for a vacuum vesel to be so light it floats?

[wumpus]

That doesn't do too much in theory though. You could in in fact have them adjacent. You double the strength but double the weight.

In the ideal case the strength requirement can always be solved by making the walls thicker (if it holds at all).
While the weight requirement can always be solved by making the walls thinner.

One difference between single and double layer airships would be that you could construct a truss between them. While a double layer may do nothing for the stress of a material to withstand the direct pressure of 15psi, I can't imagine that it would do anything to prevent the buckling of so large a surface. Consider one surface modeled as an unsupported surface covering a large hole. Instead of gravity pushing down on the surface with the weight of the surface, you would have air pressure pushing on the surface at air pressure: it would equal a surface weighing 15lbs/sq inch. It is obvious that a strut would be stronger to maintain the shape of the structure, but I don't know if it would help at all to prevent leaks.

[jayem]

One difference between single and double layer airships would be that you could construct a truss between them. While a double layer may do nothing for the stress of a material to withstand the direct pressure of 15psi, I can't imagine that it would do anything to prevent the buckling of so large a surface. Consider one surface modeled as an unsupported surface covering a large hole. Instead of gravity pushing down on the surface with the weight of the surface, you would have air pressure pushing on the surface at air pressure: it would equal a surface weighing 15lbs/sq inch. It is obvious that a strut would be stronger to maintain the shape of the structure, but I don't know if it would help at all to prevent leaks.

I had allowed room for practice to not be the same as theory :)

You could have the struts inside of the shell anyway. You lose the advantage of having the inside edges already there but gain the half-air space. I don't know how that compares, but think it's going to be negligible differences.
I think the buckling issues still scale the same (they do for Euler's columns).

I'd imagine it would help reduce the effect of leaks, if the inner shell is holed you gain no air, but the outside layer now takes the full pressure force, however the inside layer is still present and can carry some of the force if it can get there safely. If the outside layer is holed you gain a bit of air and now the inside layer takes the full pressure force. If the whole structure had say 150% margin of safety then the holed structure might just be on the margin

Molecular Hydrogen has an atomic mass of slightly more than 2. .

I won't say how long I was thinking I'm sure Tritrium in the minority. But what's wrong with Hydrogen radicals. Or hydrogen ions, that way you get a whole nother pressure term, and can reduce your mass to a couple of percent. (neither option meant seriously)

[Rockphed]

I won't say how long I was thinking I'm sure Tritrium in the minority. But what's wrong with Hydrogen radicals. Or hydrogen ions, that way you get a whole nother pressure term, and can reduce your mass to a couple of percent. (neither option meant seriously)

Molecular hydrogen is the natural state thereof under conditions similar to earth's atmosphere. I suppose if you wanted to flood your bag with high energy light to keep the hydrogen as atomic hydrogen, you could, but you would be saving 3% of your mass for a massive increase in energy expenditure and an even higher likelyhood that your system will experience catastrophic failure. I'm fairly certain you wouldn't be able to get a UL label.

[Peelee]

But what's wrong with Hydrogen radicals.

Well, their heyday was in the '60s. Now they look down on anyone doing the same thing they did back in the day.

[factotum]

Well, their heyday was in the '60s. Now they look down on anyone doing the same thing they did back in the day.

Isn't that hydrogen hipsters, not radicals?

Anyway, I think we're still at the point of asking why anyone would even attempt to do this for a very marginal increase in lifting capacity. I just can't see a practical application, and even as a thought experiment, you'd require materials far lighter and stronger than we currently possess to make this possible.

[Rockphed]

Isn't that hydrogen hipsters, not radicals?

Anyway, I think we're still at the point of asking why anyone would even attempt to do this for a very marginal increase in lifting capacity. I just can't see a practical application, and even as a thought experiment, you'd require materials far lighter and stronger than we currently possess to make this possible.

You only need to get aluminum 50% stronger than the current maximum. Well, probably more if you want to be able to actually lift anything instead of having a neutrally buoyant ball the size of a football arena.

[factotum]

You only need to get aluminum 50% stronger than the current maximum.

OK, we can tell you're not an engineer. You don't use materials that are only just capable of withstanding the loads you're putting on them, because if an extra stress is applied (say, the wind blows your vacuum airship into its mooring tower) you get catastrophic failure. An engineer will build things to be as strong as they need to be to withstand expected stress situations, and then typically add 50% on top to account for *unexpected* stress situations. When they *don't* do that, you get situations like the R101, which crashed because it could only barely fly in the first place and thus struggled when it hit unexpectedly poor weather.

[Rockphed]

OK, we can tell you're not an engineer. You don't use materials that are only just capable of withstanding the loads you're putting on them, because if an extra stress is applied (say, the wind blows your vacuum airship into its mooring tower) you get catastrophic failure. An engineer will build things to be as strong as they need to be to withstand expected stress situations, and then typically add 50% on top to account for *unexpected* stress situations. When they *don't* do that, you get situations like the R101, which crashed because it could only barely fly in the first place and thus struggled when it hit unexpectedly poor weather.

I'm not a mechanical engineer. And I am currently in "can it be done" mode, so I was going for the bare minimum to even get neutral buoyancy. What we really want is to improve on the abilities of Helium. If we wanted a vacuum balloon that was better than Helium with a shell with 50% thickness margin, we would need something as light as Aluminum with a compressive strength of 640 Mpa. Titanium is about twice the density of Aluminum and only has a strength in the low-to-mid 700s.

[Peelee]

OK, we can tell you're not an engineer. You don't use materials that are only just capable of withstanding the loads you're putting on them, because if an extra stress is applied (say, the wind blows your vacuum airship into its mooring tower) you get catastrophic failure. An engineer will build things to be as strong as they need to be to withstand expected stress situations, and then typically add 50% on top to account for *unexpected* stress situations. When they *don't* do that, you get situations like the R101, which crashed because it could only barely fly in the first place and thus struggled when it hit unexpectedly poor weather.

Yes, but it also gave us a fantastic Iron Maiden song.

[LordEntrails]

Factotum had it right. And you do know the engineers in the crowd are just laughing at speculation and assumptions in this thread right?

We've had this discussion before, and it was just as imaginative as this one. There are many many reasons why a lighter than air vessel is inferior to current solutions. Even if all of the speculative theories and "if we only had a material..." could actually be obtained.

But hey, don't let me rain on your parade, it's amusing to watch.

[Peelee]

But hey, don't let me rain on your parade

Ya know, engineers of old invented things to deal with rain.

[Rockphed]

Ya know, engineers of old invented things to deal with rain.

Now I am wondering how much energy it would take to vaporize incoming rain before it hit my head. And how thoroughly I would cook my liver if I tried to use microwaves to deliver that energy.

[factotum]

Now I am wondering how much energy it would take to vaporize incoming rain before it hit my head.

A lot, I'd say--water is surprisingly difficult to vapourise. Also, that would probably just mean you'd get hot steam hitting your head instead of cold water, not sure it would be an improvement...

[Rockphed]

A lot, I'd say--water is surprisingly difficult to vapourise. Also, that would probably just mean you'd get hot steam hitting your head instead of cold water, not sure it would be an improvement...

Well, assuming that the rain is 5 degrees celcius and is falling at about 1 inch per hour, then it would only take 17,514 W to keep the 1 square meter space I am standing in dry. If I wanted to provide that heat with methane, I could do it by burning 350g of methane every second. That is only 632 liters of natural gas every second. If I were to use microwaves, I would need higher energy output and I would probably have more losses getting the energy to the space above my head. Also, getting all of the energy into the rain without reflection would be a problem. Finally, the FCC would probably want to have words with me. 17 kW transmitters without a license tend to be frowned upon.

(And yes, that is if all of the energy from burning methane goes into vaporizing water. Presumably there would need to be some extra to keep the fire going and to account for light and heat escaping in a horizontal direction.)

[Lvl 2 Expert]

Well, assuming that the rain is 5 degrees celcius and is falling at about 1 inch per hour, then it would only take 17,514 W to keep the 1 square meter space I am standing in dry. If I wanted to provide that heat with methane, I could do it by burning 350g of methane every second. That is only 632 liters of natural gas every second. If I were to use microwaves, I would need higher energy output and I would probably have more losses getting the energy to the space above my head. Also, getting all of the energy into the rain without reflection would be a problem. Finally, the FCC would probably want to have words with me. 17 kW transmitters without a license tend to be frowned upon.

(And yes, that is if all of the energy from burning methane goes into vaporizing water. Presumably there would need to be some extra to keep the fire going and to account for light and heat escaping in a horizontal direction.)

This neatly represents this thread though. It's an interesting question to think about, it has partial answers with cool repercussions, and it's not going to catch on soon and quite possibly never because of inherent disadvantages over conventional alternatives, like roofs and coats. That indeed does not mean we should be raining on the vacuum ship parade, the parade should just be clearly hypothetical in nature so the most fun can be had with it.

[Lord Torath]

Now I am wondering how much energy it would take to vaporize incoming rain before it hit my head. And how thoroughly I would cook my liver if I tried to use microwaves to deliver that energy.

Wonder no more! Randall Munroe has got you covered!

Spoiler alert: Your are not wrong in your assumption that it would be hazardous to your health.

[Rockphed]

Wonder no more! Randall Munroe has got you covered!

Spoiler alert: Your are not wrong in your assumption that it would be hazardous to your health.

Frankly, wearing a giant bunsen burner on my head sounds much more reasonable than having a giant laser try to keep me dry. It would still probably turn my surroundings into a human sized autoclave.

[LordEntrails]

Frankly, wearing a giant bunsen burner on my head sounds much more reasonable than having a giant laser try to keep me dry. It would still probably turn my surroundings into a human sized autoclave.

An umbrella is sounding smarter and smarter :)

[Rockphed]

An umbrella is sounding smarter and smarter :)

See, if we hadn't had this discussion, you would only suspect that. You wouldn't know that!

[Peelee]

What about a vacuum umbrella that floats above my head?

[LordEntrails]

What about a vacuum umbrella that floats above my head?

Why vacuum? Just turn one upside down and put a drain in the handle and a hose to trail behind you...