3 ms·
Pure vacuum would work[1] but Hydrogen is already very sparse at atmospheric pressure. Swapping 22 litres of air at 28 grams for Hydrogen gets you 22 litres of
by jodrellblank 3y ago
Pure vacuum would work[1] but Hydrogen is already very sparse at atmospheric pressure. Swapping 22 litres of air at 28 grams for Hydrogen gets you 22 litres of Hydrogen at 2 grams[2]. That's 93% of the mass gone at much the same pressure so you can contain it in an easy bag. Swapping that Hydrogen for vacuum knocks off 2 grams but you nead a much stronger (heavier) container, and risk a massive implosion in the case of damage.
[1] https://en.wikipedia.org/wiki/Vacuum_airship https://en.wikipedia.org/wiki/Vacuum_airship
[2] Quantity estimates taken from first DuckDuckGo result which didn't look ad-filled: https://socratic.org/questions/is-hydrogen-more-or-less-dense-than-air https://socratic.org/questions/is-hydrogen-more-or-less-dens...
- hinkley 3y agoYou’d have to have internal baffles that slowed the implosion down, which would increase the weight more and also mean you aren’t going to achieve particularly hard vacuum. The internet tells me that a soda can weighs 14 grams, and those are only strong under tension, and hold half a liter. I really like the idea of evacuated structural members, but it doesn’t seem practical. Even internal bracing might be better exposed to the lifting gas rather than made air tight. But is there a sweet spot where running 0.# atmospheres of hydrogen or helium inside of a braced envelope results in lower mass per unit volume? If the skin can handle 2 psi surely it can also handle -2 psi?
- deleted 3y ago[deleted]
- plasticchris 3y agoBut under negative pressure leaks mean replacement with air, reducing lifting capacity immediately. Positive pressure would give more margin.