5 ms·

Its a cool idea but as the post suggests air pressure on the vacuum spheres is a major problem. The crush force on the sphere will scale 40x the lift factor. So

Its a cool idea but as the post suggests air pressure on the vacuum spheres is a major problem. The crush force on the sphere will scale 40x the lift factor. So 1 gram of lift, 40 grams of crush. Once you reach scales of 10,000 kilograms you'll be dealing with keeping 400,000 kilograms of weight out of your vacuum.

shadowmint 12y ago
Its worth noting that this force is not due to air preasure per se, but the difference in prrssure between the inner and outer volumes; if you can distribute the 'crush force' over a series of concentric partially pressured shells for example, the force is significantly reduced. ...not sure how it would apply to balloons, but its used in a number of things to contain high pressure on the inner ring.
- valarauca1 12y ago
  Technically true, but then that weights more. So you change the mass to mass to lift ratio.
idlewords 12y ago
The advantage over hydrogen at atmospheric pressure is really minor, too.
- dredmorbius 12y ago
  Other than vacuum not burning.
  - idlewords 12y ago
    Yeah, your balloon just implodes at the speed of sound. In terms of disastrous outcomes, it's pretty much the same thing. Hydrogen explosions are scary, but the ball of flame also rises very quickly. Most of the people on the Hindenburg survived.
    - panzi 12y ago
      I wonder what would have happened if a Vacuum airship would have had a similar accident. Meaning a hull breach at a 200m (650ft) altitude. No fire, just a bit of a drop. Maybe shrapnel? Well, I guess it would drop much faster.
      - dredmorbius 12y ago
        Given that there are no vacuum containment systems large enough to support the Hindenberg, it would never have taken off in the first place. Given that what precipitated the failure of the Hindenberg appears to have been either an initial slow leak which caught fire, or a fire which consumed the gas envelopes, possible as little as a gradual loss of lift. Even in the case of sudden failure, it would depend on how many lift compartments existed -- you'd lose 1/n of your total lift, so presumably a pronounced but possibly controlled descent.
- porpoisemonkey 12y ago
  That's true for buoyancy but vacuum definitely has a major advantage in area of flammability.
  - k__ 12y ago
    What happens if a vacuum sphere that can lift 10t implodes?
    - dredmorbius 12y ago
      You lose 10t of lift. If a hydrogen envelope of 10t ruptures, you lose 10t of lift and have a major fire hazard.
      - idlewords 12y ago
        You lose 10t of lift in a horrifyingly destructive implosion: https://www.youtube.com/watch?v=Zz95_VvTxZM https://www.youtube.com/watch?v=Zz95_VvTxZM
        dredmorbius 12y ago
        And here's what hydrogen does. Note the comparison is of a pure H₂ vs. 2 χ H₂ + O₂ mix. https://www.youtube.com/watch?v=qOTgeeTB_kA https://www.youtube.com/watch?v=qOTgeeTB_kA
      - ars 12y ago
        Hydrogen is not as major of a hazard as it looks. It's lighter than air, and will rapidly leave if it escapes. The real trick is making sure no oxygen gets in. In contrast a leak is not super dangerous. It will still burn of course, but if the skin is flameproof it won't do much harm to the ship as a whole. So what you do is make sure it's enclosed in cells of a flameresistant material. That way a fire won't spread and will rapidly rise away and put itself out.
        dredmorbius 12y ago
fabulist 12y ago
Would another shape reduce the amount of surface area/external pressure? I've long dreamed of having one of these ships, but it doesn't seem to be in the cards.
- danbruc 12y ago
  No, a sphere has the minimal surface area volume ratio. Wait, that does not really answer your question.
  - valarauca1 12y ago
    Yes it does. It would be a major mathematical revolution if you discovered a new shape that exists in our world that has a better SA:V ratio.
    - olefoo 12y ago
      But SA/V isn't the important ratio here. The important ratio is weight to volume. Surface area only matters in terms of how much pressure the system needs to resist, and using compression members means you have some room to play with. But if you have a a structure from which you've removed the air that is too heavy to float in air you get no prize.
      - lutusp 12y ago
        > But SA/V isn't the important ratio here. The important ratio is weight to volume. Don't forget crush resistance with a minimum of construction material. But as it turns out, a spherical shell is the optimal shape for all the stated requirements -- it evenly distributes the compressive force across its surface, it represents the optimal ratio of surface area to volume, and it therefore follows that a sphere represents the smallest mass per enclosed volume. > But if you have a a structure from which you've removed the air that is too heavy to float in air you get no prize. That's certainly true. But for a vessel with a fixed wall thickness, making it larger greatly increases the chance that it will rise, because the enclosed volume increases so much faster than the surface area. This would all be easier on Venus, where the atmospheric pressure is vastly greater than here, but the gravitational force is less. If only it weren't so damn hot.
pkinsky 12y ago
Could you get around this by using many small vacuum-filled spheres instead of one large sphere?
- valarauca1 12y ago
  The scaling of sphere SA to Volume isn't exactly linear, its more logarithmic Source: http://upload.wikimedia.org/wikipedia/commons/thumb/5/5f/Comparison_of_surface_area_vs_volume_of_shapes.svg/512px-Comparison_of_surface_area_vs_volume_of_shapes.svg.png http://upload.wikimedia.org/wikipedia/commons/thumb/5/5f/Com...
- pantalaimon 12y ago
  sure, but many small spheres are heavier than a large one.
  - dredmorbius 12y ago
    More specifically: weight/lift ratio is a cube to square relationship. Lift increases with the cube of the radius, weight (of the envelope) with the square. So a collection of smaller spheres would have a higher mass.

shadowmint 12y ago

Its worth noting that this force is not due to air preasure per se, but the difference in prrssure between the inner and outer volumes; if you can distribute the 'crush force' over a series of concentric partially pressured shells for example, the force is significantly reduced. ...not sure how it would apply to balloons, but its used in a number of things to contain high pressure on the inner ring.

valarauca1 12y ago
Technically true, but then that weights more. So you change the mass to mass to lift ratio.

idlewords 12y ago

The advantage over hydrogen at atmospheric pressure is really minor, too.

dredmorbius 12y ago
Other than vacuum not burning.
- idlewords 12y ago
  Yeah, your balloon just implodes at the speed of sound. In terms of disastrous outcomes, it's pretty much the same thing. Hydrogen explosions are scary, but the ball of flame also rises very quickly. Most of the people on the Hindenburg survived.
  - panzi 12y ago
    I wonder what would have happened if a Vacuum airship would have had a similar accident. Meaning a hull breach at a 200m (650ft) altitude. No fire, just a bit of a drop. Maybe shrapnel? Well, I guess it would drop much faster.
    - dredmorbius 12y ago
      Given that there are no vacuum containment systems large enough to support the Hindenberg, it would never have taken off in the first place. Given that what precipitated the failure of the Hindenberg appears to have been either an initial slow leak which caught fire, or a fire which consumed the gas envelopes, possible as little as a gradual loss of lift. Even in the case of sudden failure, it would depend on how many lift compartments existed -- you'd lose 1/n of your total lift, so presumably a pronounced but possibly controlled descent.
porpoisemonkey 12y ago
That's true for buoyancy but vacuum definitely has a major advantage in area of flammability.
- k__ 12y ago
  What happens if a vacuum sphere that can lift 10t implodes?
  - dredmorbius 12y ago
    You lose 10t of lift. If a hydrogen envelope of 10t ruptures, you lose 10t of lift and have a major fire hazard.
    - idlewords 12y ago
      You lose 10t of lift in a horrifyingly destructive implosion: https://www.youtube.com/watch?v=Zz95_VvTxZM https://www.youtube.com/watch?v=Zz95_VvTxZM
      - dredmorbius 12y ago
        And here's what hydrogen does. Note the comparison is of a pure H₂ vs. 2 χ H₂ + O₂ mix. https://www.youtube.com/watch?v=qOTgeeTB_kA https://www.youtube.com/watch?v=qOTgeeTB_kA
    - ars 12y ago
      Hydrogen is not as major of a hazard as it looks. It's lighter than air, and will rapidly leave if it escapes. The real trick is making sure no oxygen gets in. In contrast a leak is not super dangerous. It will still burn of course, but if the skin is flameproof it won't do much harm to the ship as a whole. So what you do is make sure it's enclosed in cells of a flameresistant material. That way a fire won't spread and will rapidly rise away and put itself out.
      - dredmorbius 12y ago

fabulist 12y ago

Would another shape reduce the amount of surface area/external pressure? I've long dreamed of having one of these ships, but it doesn't seem to be in the cards.

danbruc 12y ago
No, a sphere has the minimal surface area volume ratio. Wait, that does not really answer your question.
- valarauca1 12y ago
  Yes it does. It would be a major mathematical revolution if you discovered a new shape that exists in our world that has a better SA:V ratio.
  - olefoo 12y ago
    But SA/V isn't the important ratio here. The important ratio is weight to volume. Surface area only matters in terms of how much pressure the system needs to resist, and using compression members means you have some room to play with. But if you have a a structure from which you've removed the air that is too heavy to float in air you get no prize.
    - lutusp 12y ago
      > But SA/V isn't the important ratio here. The important ratio is weight to volume. Don't forget crush resistance with a minimum of construction material. But as it turns out, a spherical shell is the optimal shape for all the stated requirements -- it evenly distributes the compressive force across its surface, it represents the optimal ratio of surface area to volume, and it therefore follows that a sphere represents the smallest mass per enclosed volume. > But if you have a a structure from which you've removed the air that is too heavy to float in air you get no prize. That's certainly true. But for a vessel with a fixed wall thickness, making it larger greatly increases the chance that it will rise, because the enclosed volume increases so much faster than the surface area. This would all be easier on Venus, where the atmospheric pressure is vastly greater than here, but the gravitational force is less. If only it weren't so damn hot.

pkinsky 12y ago

Could you get around this by using many small vacuum-filled spheres instead of one large sphere?

valarauca1 12y ago
The scaling of sphere SA to Volume isn't exactly linear, its more logarithmic Source: http://upload.wikimedia.org/wikipedia/commons/thumb/5/5f/Comparison_of_surface_area_vs_volume_of_shapes.svg/512px-Comparison_of_surface_area_vs_volume_of_shapes.svg.png http://upload.wikimedia.org/wikipedia/commons/thumb/5/5f/Com...
pantalaimon 12y ago
sure, but many small spheres are heavier than a large one.
- dredmorbius 12y ago
  More specifically: weight/lift ratio is a cube to square relationship. Lift increases with the cube of the radius, weight (of the envelope) with the square. So a collection of smaller spheres would have a higher mass.