I know that with a vacuum, you'll be able to gain a whole lot more lift than with any gas. I'm just wondering how you'd do it. What would be needed to make a vacuum balloon as opposed to a hot-air balloon?

• A vacuum doesn't provide a whole lot more lift than hydrogen or helium already do in our atmosphere. A given volume of vacuum would provide only 16% more lift than an equal volume of helium and only 7% more than an equal volume of hydrogen. en.wikipedia.org/wiki/Lifting_gas#Vacuum – Mike Nichols Mar 4 '15 at 23:55
• @MikeNichols Would a thicker atmosphere make a bigger difference? – Desolationgame Mar 5 '15 at 0:10
• The thicker the atmosphere, the more lift vacuum generates. – Jorge Aldo Mar 5 '15 at 1:58
• @user4627545 Depends on what you mean by thicker. If you mean the atmosphere has a higher pressure and is therefore denser, the buoyancy of vacuum and of any lighter gasses would increase, but by the same proportion so vacuum would still only be 7% more effective than hydrogen. However, if by thicker you mean denser constituent gasses that would cause a vacuum to generate more lift, but it would actually lose its advantage over lifting gasses as the atmosphere became more dense. – Mike Nichols Mar 5 '15 at 4:47
• @user4627545 On the other hand an atmosphere made of lighter gasses would increase vacuum's advantage over hydrogen and helium. For instance in an atmosphere made of helium a vacuum would have nearly twice the lifting power of hydrogen. – Mike Nichols Mar 5 '15 at 4:48

The other answers discuss normall matter physical materials, where it seems unlikely to be possible or practical.

However, that's not the only option. As mentioned on other posts (shields, super materials, etc.). I have been convinced that practical warm superconductors will be an enabling and transformative technology.

Besides simply saying "build the ball out of the afore-mentioned supermaterial", this case is simple, and similar to the original application described for the technology in space construction: make a loop of superconductive rope and install a permanent current. Its self-magnetism will turn the wire into a hoop.

The awsome thing about magnetic structues is that the strength is unlimited in the classic sense. Anything that would deform the structure applies energy that's used to resist the movement instead! A hoop, used to make a rib of a balloon, will distribute the pressure uniformly and have no weak point to fail at, since it's just magnetism and electric current.

What's really cool is that the physical material is just flexible string. When turned off, it is shipped flat and folded into a compact container. To use, it is charged with electricity. Flux-pinning technology is used mount the balloons and other vehicle components together.

• Of course! Why didn't I think of this? I think I've even seen this idea somewhere before – Desolationgame Jun 16 '16 at 17:18
• Yes, likewise! I've pondered superconductor tech before. – JDługosz Jun 16 '16 at 17:27
• If I allowed for a discovered room-temperature superconductor in my world, what other implications would this mean? What else is possible, and what would the first practical uses to be developed or thought up? – Androconus Oct 31 '16 at 0:36
• @Androconus see here, here, etc. – JDługosz Oct 31 '16 at 2:39

The strength needed for any material to sustain a vacuum in any meaningfull volume while at the same time keeping buoyancy in our atmosphere is way above current material technology knowledge. You need strong walls to hold a vacuum against the atmospheric pressure, at the same time you need light enough walls, so as to avoid adding weight to the system and end up having something that is still heavier than air. Buoyancy is achieved when the volume of the system vacuum + walls weight less than the same volume of air.

This is simply not possible with known materials.

• I was hoping to science-fiction away material requirements – Desolationgame Mar 4 '15 at 23:29
• This answer only holds true if we are talking about earth's atmosphere. In other planets your mileage may vary. – Jorge Aldo Mar 6 '15 at 21:46
• @JorgeAldo You may be able to get a vacuum airship to float in a denser atmosphere, but you couldn't get it to float better than a helium airship. In fact, your vacuum balloon's gondola would probably be more buoyant than the vacuum chamber it hangs from. – Mikkel Jan 12 '18 at 18:05

The idea has been around for about 345 years in the form of a Vacuum Airship. As the Wikipedia page goes on to say, even a diamond sphere can not be used to hold a volume of vacuum large enough to displace its own mass in air.

However, this patent, claims it is possible with a honeycomb material for the spherical shell. But if that's true, one wonders why we haven't seen any vacuum airships flying around. But, it's likely due to the possible violent implosion of the spheres.

Perhaps when we run out of helium, this will be further investigated and we'll start getting vacuum dirigible drones delivering Amazon packages (not blimps, as Burki pointed out, as the shell will necessarily be rigid).

• Only it would not be a blimp, since the vacuum chambers would be rigid. But yes... i know... :-) – Burki Mar 5 '15 at 8:05
• @Burki You got me there :) I somehow managed to be full of hot air. – Samuel Mar 5 '15 at 17:31
• "possible violent implosion" only if the shell looses integrity when pierced. Otherwise, the balloon could simply fill with air rapidly, and the balloon fall. – njzk2 Dec 5 '16 at 3:39

I've been considering the possibility of carbon nanospheres. If they are formed in a vacuum, they'd contain vacuum. They'd have to be fairly large (I'm not mathematician enough to calculate how large), but if they were large enough and didn't collapse, they'd be lighter than an equivalent volume of air or even hydrogen. However I'm not sure if they'd be strong enough to withstand air pressure, though carbon compounds are pretty strong.

If carbon nanospheres are strong enough to withstand atmospheric pressure, then you'd basically fill a container with a whole lot of them, and presto! It floats.

The advantage of nanospheres is that if your container is damaged, you might lose some of your nanospheres, but you are unlikely to lose all of them. The nanospheres may even stay in a compromised container if they are large enough and the holes in the container are small enough, so such a system would be damage tolerant, to the degree that you wouldn't have a near-instant loss of lift.

• Well, the density of bucky-balls (carbon nanospheres) is over 1300 times more than air, so those won't work. I'm not aware of stable larger configurations other than $C_{70}$. Besides, I think much larger and air molecules can get in, the smaller ones might be able to already. – Samuel Mar 5 '15 at 1:27
• There is a thing called aerogel, they are colloidal substances were the liquid component is removed by a non-destructive method. This results in a mesh of the solid. This aerogel, even if evacuated with vacuum does not float. aerogeltechnologies.com/faqs – Jorge Aldo Mar 5 '15 at 2:14