3 ms·
Since we always choose the lightest / least dense possible lifting gas, would it be possibly to use a pure vacuum as a lifting gas? You'd need an insanely stron
by joshmarinacci 3y ago
Since we always choose the lightest / least dense possible lifting gas, would it be possibly to use a pure vacuum as a lifting gas? You'd need an insanely strong cover and internal structure, but would it theoretically work?
And if not a pure vacuum about using regular air and then pumping out the air until you reach a partial vacuum that meets your current lifting needs?
- rsynnott 3y agoIt would work, if you had magic impossible materials, yes. However it wouldn't actually provide _that_ much more lift than hydrogen. Vacuum airships largely show up in sci-fi, as a sign that someone is showing off (they require absolute magic materials technology, but aren't really all that useful). Iain M Banks liked them.
- aidenn0 3y agoAlso if you had those magic impossible materials, you could probably use even less of them with hydrogen for greater lift than more of them with a vacuum.
- tastyfreeze 3y agoTheoretically, yes. The insanely strong structure is the problem. The required strength is too heavy to be lifted by the vacuum. http://cba.mit.edu/docs/papers/19.01.vacuum.pdf http://cba.mit.edu/docs/papers/19.01.vacuum.pdf
- rtkwe 3y agoEven if you could build it so that it is positively buoyant you're only saving a 1-2 grams per liter of helium you replace with vacuum. He and H are extremely good at being light filler gasses.
- RandallBrown 3y agoI guess it's theoretically possible, but not really on earth. https://en.wikipedia.org/wiki/Vacuum_airship https://en.wikipedia.org/wiki/Vacuum_airship
- jodrellblank 3y agoPure 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.
- clbrmbr 3y ago14lbs/in2 adds up fast ;) A back-of-the-envelope calculation shows that a 100m sphere would have 600 million pounds of force on its surface area.
- suoduandao3 3y agoThe Diamond Age involves that, surrounded by 3D printed diamond. No idea how quickly nitrogen would actually diffuse across three inches of diamond with a 1-ATM pressure difference, but it sure sounded cool.
- adastra22 3y agoIf you have atomically precise manufacturing of diamond, then you might as well have efficient molecular pumps to maintain that vacuum.
- rtkwe 3y agoThink about atmospheric pressure, it is 14.7 PSI at the ground so your envelope has to be extremely strong to hold that pressure differential if you want to use vacuum instead of filling it with a lighter gas. Helium is only 0.1786 g/L at STP. So unless you're saving more weight than that over your entire envelope it's better to just fill it with a gas and have a significantly lighter lifting envelope.
- JumpCrisscross 3y agoThe key is to realise the gas is exerting force against the atmosphere through the lining. It isn’t dead weight, it’s doing work.
- plasticchris 3y agoSure, at ground level. If instead we make these in orbit and drop them slowly…
- rtkwe 3y agoThe lower the pressure the less difference between the outside and inside so less buoyancy.
- bee_rider 3y agoAnother option would be to float the craft on a denser fluid, which means the lifting gas could be lighter. For example, most of the Earth is covered in salt water, perhaps we could design some sort of “water ship.”
- isk517 3y agoThis is the kind of thinking we get from people that grew watching and reading high fantasy such as 'Master and Commander' and 'Horatio Hornblower'.
- woah 3y agoIncredible... you could use ambient air as the lifting gas
- plasticchris 3y agoPfft been done, just heat it up
- gpm 3y agoWe've tried this but the heavier fluid surrounding such craft requires so much more structural strength that it's just not worth it for anything but niche applications like stealth or viewing the bottom of the sea floor. And I have no interest in people who are always sitting on the fence.
- fooker 3y agoWould require a structure light enough to prevent implosion. This does not exist.
- pengaru 3y ago> Since we always choose the lightest / least dense possible lifting gas, would it be possibly to use a pure vacuum as a lifting gas? You'd need an insanely strong cover and internal structure, but would it theoretically work? Theoretically, but you'd be incentivized to cut weight as much as possible in the pressure vessel department... might as well put OceanGate logos on the control surfaces.