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Comment by yoz-y | Hacker News Reader

A completely naïve question: Is there any chance we could get buoyancy from void if the materials are strong enough?

Don't know about the material science behind it. But from a purely physical point of view, the problem there is that void (= vacuum) does not have any pressure. So the frame would have to support itself against the atmospheric pressure instead of the gas doing it from the inside – that is a big technical challenge. The catastrophic failure scenario (hull breach) would be an implosive compression of the entire hull, which kinda sounds worse than a hydrogen-fuelled fire.

If luck was kind there might be a sweet spot making it possible to make a small lighter-than-air vaccume hull, and then add a lot of those to a craft. Something suspiciously like attaching a large number of balloons to a frame. Maybe some wonder material; carbon seems to do everything according to the headlines.

That'd solve the implosion problem since presumably all the little hulls wouldn't fail at once.

I read about this a lot a while ago, the main solution I came across was that in the diamond age when we get to that point in societal development. We'll be able to make tiny diamond bubbles with a vacuum inside, and they can be used to create airships and floating platforms. The airship doesn't have to be a single large vacuum diamond hull, but could also be made from many smaller diamonds which would help prevent a catastrophic failure. The diamond bubbles would be strong and light enough to hold the vacuum.

The wikipedia entry on "vacuum airships, as they're called," is nicely detailed. https://en.wikipedia.org/wiki/Vacuum_airship

If I remember correctly, one of Edgar Rice Burroughs' Pelucidar books involves a vacuum airship as well. His was just made of some sort of future super strong unobtainium type matterial though.

Vacuum has only around 10% (iirc) more buoyancy than hydrogen in the atmosphere, so the gains would be very minimal while the added constraints due to having such a large pressure difference would be huge.

Vacuum airships are an interesting concept but have not advantage compared to gas airships in practice.

I see at least two advantages: compared to hydrogen they are not flammable and compared to helium they don't require a limited resource.

You'd need a very heavy chamber to keep the vacuum balloon from collapsing.

Hook up a vacuum pump to a flask. It isn't going to rise as the air is pumped out. Edison's light bulbs did not float.

> You'd need a very heavy chamber to keep the vacuum balloon from collapsing.

That was my original question: is it technically feasible to make such a chamber from light enough materials (my first guess would be some carbon tubes supporting a carbon fiber tarp or something like that.

> Edison's light bulbs did not float.

One could argue that it was too small (of course I imagine making a massive lightbulb would not make for a good solid structure, also glass is heavy). A hot air balloon does not float either if you lest it too much.

This topic has been discussed for ages, but no feasible solution has been found as of yet.[1]

https://en.wikipedia.org/wiki/Vacuum_airship

It is worth noting that at a helium balloon's upper altitute, vacuum balloons would be more feasable as the air pressure allows thinner materials. Some sort of hybrid for say weather monitoring might be feasable.

Partial vacuum on a steel railroad tank car, for comparison.

https://www.invidio.us/watch?v=Zz95_VvTxZM

Vacuum airships have a long history: "First proposed by Italian Jesuit priest Francesco Lana de Terzi in 1670"[0]. The O-Boot project referenced in some replies aims to fly its first prototype on 13 December 2019 because that is the anniversary of the birth of Francesco Lana.

We'll see, but maybe it is like nuclear fusion energy - always just around the corner.

[0] https://en.wikipedia.org/wiki/Vacuum_airship

Maybe? https://www.o-boot.com/en/

"Our goal is the presentation of the first vacuum airship in history in Brescia on December 13th of this year [2019], for the anniversary of Francesco Lana, the Brescian inventor of vacuum airship, who was baptized in Brescia on December 13th 1631."

My completely uninformed guess: structures strong enough to not be collapsed by the void would be heavy to the point that the combination of void+containment would not be buoyant.

I'd try a huge sphere of polyamide aerogel, wrapped in an aluminum shell, then evacuated. If that didn't work, I'd give up immediately, because vacuum lifters are stupidly difficult when hydrogen exists.

Okay, I wouldn't give up immediately. I'd also try a vacuum onion, with multiple layers of aerogel and aluminum, with each successive layer evacuated to a different pressure.

Yes. But in general you need heavier materials to resist the external pressure (cave in), than materials that need to resist the (inwards) pressure.

In theory, completely possible. In practice, strong enough materials to hold a vacuum are too heavy and nullify the buoyancy.

From https://www.o-boot.com/en/faq/

8<-----------------------snip

6) Have you done structural calculations on the vacuum ballon yet? What material can be strong enough to withstand air pressure and light enough to rise in flight?

There are two models: a basic model and an evolution model. The first one, on which a degree research was done at the Polytechnic of Turin, is a sandwich with ceramic skins and foam in between. This model is lighter than air (obviously if emptied of inner air) and holds an external pressure (with zero internal pressure) up to 1.7 atm.

The second model should withstand a similar external pressure but be lighter and easier to build. If you want, you leave us your email, and we send you the research thesis that was made on the first model, with all the structural calculations. Unfortunately, all information regarding the second model is confidential.

8<-----------------------snip

Fingers crossed for December 13th!

I'm imagining a zeppelin that looks like a starfruit, an evacuated structural fabric over a compression frame.

A monoatomic planar fractal void of some description might work. Sarpinsky triangle or Menger sponge.

A very distant possibility.

There is real no reason to, hydrogen and helium lift approximate the same.

But yes, a vacuum lifts approximately 10% better than hydrogen.

So whatever the structure is, if filled with hydrogen or helium it'd work similar.

If you have some sort of mesh holding in a vacuum it's hard to see it's average density being less than hydrogen or helium or even air at the end of the day.

Point is, everything is possible now. A void wouldn't value add.

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