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Question: will it ever be possible to wrap a thin impermeable film around a structure like that, suck out the air inside and end up with a lighter-than-air sol

Question: will it ever be possible to wrap a thin impermeable film around a structure like that, suck out the air inside and end up with a lighter-than-air solid in order to build vacuum airships?

sandworm101 10y ago
Theoretically yes, practically no. But why bother? Supporting the walls by filling the space with a gas lighter than air would be more efficient.
- knodi123 10y ago
  Theoretically, no, not this particular substance. But anyway, the reason people are fascinated with the idea is that vacuum is a renewable and abundant resource. Heck, space is almost completely full of it. All of the lighter-than-air gases I'm aware of have downsides, like hydrogen's permeability and flammability, or helium's rarity and price.
  - sandworm101 10y ago
    If the container is going to be metal, then hydrogen is an option. I wonder about flammability. This substance is metal with an extremely high surface area/volume ratio. It may be very flammable, and potentially contain much greater energies, when mixed with air.
    - the8472 10y ago
      > If the container is going to be metal, then hydrogen is an option. Afaik hydrogen tends to slowly diffuse through metals and embrittle and corrode them in the process. And a solid-metal hull probably is ideal for airships anyway.
    - astrodust 10y ago
      Pure hydrogen doesn't burn, it needs oxygen. The Hindenburg disaster was so spectacular because the ship was made out of highly flammable canvas and wood. The hydrogen itself burned up very quickly once escaping. If the ship had been made out of metal it would've sprouted a brief jet of flame, then crunched to the ground in a fairly ungraceful manner, but it wouldn't have exploded. Maybe a graphene hydrogen containment cell could work? That would be strong enough to deal with the pressure, plus provide a flame resistant barrier.
      - skykooler 10y ago
        Graphene is flammable, as are pretty much all arrangements of pure carbon.
        astrodust 10y ago
        Everything is flammable if you can heat it up enough and get it ready to party with oxygen. It could be treated with some kind of fire-retardant chemical, though.
  - VLM 10y ago
    Hot air is lighter than air, and aerogel like low density materials have some weird property where the thermal conductance is lower than bare gas when the mean free path in the aerogel is shorter than the mean free path in bulk gas. In other words they're better hot air balloons than actual hot air balloons. Something interesting to think about is if they don't leak heat energy very well, and the exterior is something heat proof (steel foil?) you can heat up the air inside to arbitrary temps until radiative glow exceeds the other thermal losses. So if you think nylon hot air balloons are high performance, imagine balloons with much higher lift per volume. A liter of air weighs about a gram so its always going to take a large piece of aerogel to lift me (I weigh quite a few grams) but ... A hot air balloon sized piece of aerogel is not economically viable right now, even for the military... or is it?
    - lgats 10y ago
      From the YouTube videos I've seen, aerogel doesn't quite float when it's heated up. Interesting theory though if a similar substance is discovered.
    - knodi123 10y ago
      Low-density materials surrounded by a thin shell are still going to weight a lot more than air surrounded by a thin shell. Also, you have to look into how this is going to be heated. For a hot air balloon to work, all the air inside has to be hot. If your balloon is filled with an amazingly efficient insulator.... Also, the reason airships use lighter-than-air gas is because then they don't have to carry lots of heavy fuel for heating air. Things like fuel, and pipes to carry heat throughout your aerogel, will rapidly eat up any efficiencies you gained.
  - ljf 10y ago
    Helium is not that rare, it's just that we choose not the capture it when digging for oil or gas. The US mine that is "running out" is a store not a source. It's just not economical to collect it from gas wells while the US is selling off the Helium reserve 'cheap'. http://m.phys.org/news/2013-04-probing-helium.html http://m.phys.org/news/2013-04-probing-helium.html
  - astrodust 10y ago
    Helium is still dirt cheap despite its relative rarity on Earth. In the universe at large it's ridiculously abundant.
- grondilu 10y ago
  A gaz is not a solid. Think about a what you could build with a solid that is lighter than air. That would make the expression "the sky is the limit" pretty much literal.
Retric 10y ago
No, this is not nearly strong enough for that. 1 square foot at 1 ATM ~= 1 ton of weight, in the video she was crushing a square in of this stuff between her fingers with relative ease.
deleted 10y ago
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Question: will it ever be possible to wrap a thin impermeable film around a structure like that, suck out the air inside and end up with a lighter-than-air solid in order to build vacuum airships?

sandworm101 10y ago

Theoretically yes, practically no. But why bother? Supporting the walls by filling the space with a gas lighter than air would be more efficient.

knodi123 10y ago
Theoretically, no, not this particular substance. But anyway, the reason people are fascinated with the idea is that vacuum is a renewable and abundant resource. Heck, space is almost completely full of it. All of the lighter-than-air gases I'm aware of have downsides, like hydrogen's permeability and flammability, or helium's rarity and price.
- sandworm101 10y ago
  If the container is going to be metal, then hydrogen is an option. I wonder about flammability. This substance is metal with an extremely high surface area/volume ratio. It may be very flammable, and potentially contain much greater energies, when mixed with air.
  - the8472 10y ago
    > If the container is going to be metal, then hydrogen is an option. Afaik hydrogen tends to slowly diffuse through metals and embrittle and corrode them in the process. And a solid-metal hull probably is ideal for airships anyway.
  - astrodust 10y ago
    Pure hydrogen doesn't burn, it needs oxygen. The Hindenburg disaster was so spectacular because the ship was made out of highly flammable canvas and wood. The hydrogen itself burned up very quickly once escaping. If the ship had been made out of metal it would've sprouted a brief jet of flame, then crunched to the ground in a fairly ungraceful manner, but it wouldn't have exploded. Maybe a graphene hydrogen containment cell could work? That would be strong enough to deal with the pressure, plus provide a flame resistant barrier.
    - skykooler 10y ago
      Graphene is flammable, as are pretty much all arrangements of pure carbon.
      - astrodust 10y ago
        Everything is flammable if you can heat it up enough and get it ready to party with oxygen. It could be treated with some kind of fire-retardant chemical, though.
- VLM 10y ago
  Hot air is lighter than air, and aerogel like low density materials have some weird property where the thermal conductance is lower than bare gas when the mean free path in the aerogel is shorter than the mean free path in bulk gas. In other words they're better hot air balloons than actual hot air balloons. Something interesting to think about is if they don't leak heat energy very well, and the exterior is something heat proof (steel foil?) you can heat up the air inside to arbitrary temps until radiative glow exceeds the other thermal losses. So if you think nylon hot air balloons are high performance, imagine balloons with much higher lift per volume. A liter of air weighs about a gram so its always going to take a large piece of aerogel to lift me (I weigh quite a few grams) but ... A hot air balloon sized piece of aerogel is not economically viable right now, even for the military... or is it?
  - lgats 10y ago
    From the YouTube videos I've seen, aerogel doesn't quite float when it's heated up. Interesting theory though if a similar substance is discovered.
  - knodi123 10y ago
    Low-density materials surrounded by a thin shell are still going to weight a lot more than air surrounded by a thin shell. Also, you have to look into how this is going to be heated. For a hot air balloon to work, all the air inside has to be hot. If your balloon is filled with an amazingly efficient insulator.... Also, the reason airships use lighter-than-air gas is because then they don't have to carry lots of heavy fuel for heating air. Things like fuel, and pipes to carry heat throughout your aerogel, will rapidly eat up any efficiencies you gained.
- ljf 10y ago
  Helium is not that rare, it's just that we choose not the capture it when digging for oil or gas. The US mine that is "running out" is a store not a source. It's just not economical to collect it from gas wells while the US is selling off the Helium reserve 'cheap'. http://m.phys.org/news/2013-04-probing-helium.html http://m.phys.org/news/2013-04-probing-helium.html
- astrodust 10y ago
  Helium is still dirt cheap despite its relative rarity on Earth. In the universe at large it's ridiculously abundant.
grondilu 10y ago
A gaz is not a solid. Think about a what you could build with a solid that is lighter than air. That would make the expression "the sky is the limit" pretty much literal.

Retric 10y ago

No, this is not nearly strong enough for that. 1 square foot at 1 ATM ~= 1 ton of weight, in the video she was crushing a square in of this stuff between her fingers with relative ease.

deleted 10y ago

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