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Just as the title says. If you pumped all the air from a balloon and somehow (handwave) kept it from collapsing. Would that balloon produce more lift than a hydrogen filled balloon? How much better would it perform?

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    $\begingroup$ someone has written a book with this tech. In the book, there was theoretically no ceiling, they would just keep going up and up till they reached space. The spheres were made of metal to keep them from ‘collapsing’. With some creative license (don’t explain how it works), you can probably get away with it. $\endgroup$ Commented May 31, 2022 at 15:43
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    $\begingroup$ As compared to a volume of air, a volume of vacuum is only a little bit lighter than that volume of hydrogen. But you need to augment the vacuum containing structure against veing crushed by air pressure; hydrogen gas resists being crushed because it is a gas., More reading here: worldbuilding.stackexchange.com/questions/87057/… $\endgroup$
    – Willk
    Commented May 31, 2022 at 15:54
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    $\begingroup$ Just wondering what the ridges might have to do with it? What's the total mass of the structure, what's the total volume displacement? $\endgroup$ Commented May 31, 2022 at 18:33
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    $\begingroup$ Vacuum balloons also feature in Neal Stephenson's The Diamond Age, where they're used to stabilize tall buildings and allow overhangs and shapes that wouldn't be possible otherwise. $\endgroup$
    – Beejamin
    Commented Jun 1, 2022 at 4:42
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    $\begingroup$ Also, James Hogan, Cradle of Saturn has it as a technology they are trying to acquire. Indestructible balloons rather than the ultra-vulnerable hot-hydrogen ones they're using on Saturn. $\endgroup$ Commented Jun 6, 2022 at 0:08

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Not very much. 1 mole of a gas occupies 22.7 litres at 0°C. One mole is the molecular mass in grams. Thus one mole of hydrogen weighs 2 grams, and one mole of air is (28 * 0.8 + 32 * 0.2) = 28.8 grams. Therefore a hydrogen blimp gives 26.8 grams/22.7litres lift (1.18 grams/litre) and a vacuum blimp gives 28.8grams/22.7 litres (1.27 grams/litre), a difference of 88 milligrams/litre.

https://en.wikipedia.org/wiki/Molar_volume#Ideal_gases

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  • $\begingroup$ Plus, of course, the vacuum blimp requires much more support. The gas version requires enough strength to not tear under the internal pressure, the vacuum version requires enough strength to not be crushed by the atmosphere. $\endgroup$ Commented Jun 1, 2022 at 8:06
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    $\begingroup$ What if instead you use compressed vaccum for more buoyancy? $\endgroup$
    – John O
    Commented Jun 2, 2022 at 18:23
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    $\begingroup$ @JohnO what's a 'Compressed Vacuum' ? $\endgroup$
    – CSM
    Commented Jun 2, 2022 at 21:28
  • $\begingroup$ Aerogels have a density of 1000g/m³ and the strength to hold an envelope filled with vacuum open against atmospheric pressure. $\endgroup$ Commented Jun 5, 2022 at 0:27

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