6 ms·
There are no really great lifting gases. Steam is ok but must be kept hot. H2 is dangerously explosive. Vacuum is the best (a so-called "null ship") but no know
by astazangasta 8y ago
There are no really great lifting gases. Steam is ok but must be kept hot. H2 is dangerously explosive. Vacuum is the best (a so-called "null ship") but no known material can maintain the hull pressure under vacuum.
- davnicwil 8y agoExcuse the silly question if it is one, but would one option be not a full vacuum but only marginally lower density of air inside the balloon, supplemented by solar-powered propellers? Could there be a material strong enough to handle a minimal density difference to provide enough lift for it to work?
- nradov 8y agoNo not even diamond is strong enough to allow generating a useful amount of lift that way.
- lawlessone 8y agoTo add to your Idea, could a "null ship" be carried to a greater height and then where the air is thinner have it's gas removed to take everything a little higher? Like rocket stages but for airships.
- astazangasta 8y agoAt a greater height you need a larger airship to provide the same lift. As you move towards the vacuum of space and the differential becomes less the lift per unit volume is less.
- lawlessone 7y agoaww :(
- astazangasta 8y agoYeah I had this idea also, steam vapor at 1/8 atm might be easier than a full vacuum. Havent done the math, though.
- jeffreyrogers 8y agoAny structure strong enough to withstand the pressure from outside the vacuum weighs too much to be lifted. At least that's what I read in some aerodynamics book. Maybe some materials scientist will come along and prove that wrong.
- beamatronic 8y agoCan we make many small ones instead of one big one?
- shkkmo 8y agoAs volumes decrease in size, the ratio of surface to volume increases, make weight a bigger issue with smaller envelopes (given that surface thickness would not be able to decrease proportionally).
- deleted 8y ago[deleted]
- andbberger 8y agoI don't think the possibility can be entirely discounted. Consider composite materials, a honeycomb. Much more difficult to analyze than a sphere of steel
- gnode 8y ago> H2 is dangerously explosive. Does it matter for an unmanned vehicle? Such a thing could be inflated at a safe distance. In some cases, being able to self destruct is a safety benefit (to prevent crashes when control is lost) and a security benefit (to prevent analysis of captured aircraft). Particularly UAVs are popular in military / spying operations.
- cr0sh 8y agoI'd argue that hydrogen is actually among the best, with helium of course being second. Helium wins out on the inertness, but has far lower lifting capacity, and of course has a supply issue. Hydrogen wins on lifting capacity, supply is not an issue at all - but it has a weird image problem, thanks to one singular accident - which was arguably not caused by the lifting gas! Prior to that accident, hydrogen had a fairly great record with airships, and it was used extensively for ballooning as well without many incidents. Hydrogen by itself isn't flammable - you need another particular gas involved for that to be an issue. You also need a source of ignition.
- evgen 8y agoThe other problem with hydrogen is that it is hard to contain. Leakage and permeability of the envelope would probably end up being a bigger engineering concern than would flammability.
- m0zg 7y agoAnd yet another problem with hydrogen is that unlike helium it is reactive, including with some metals. And those metals tend to become brittle fall apart after a while: https://en.wikipedia.org/wiki/Hydrogen_embrittlement https://en.wikipedia.org/wiki/Hydrogen_embrittlement
- philipkglass 7y agohttp://usa.dupontteijinfilms.com/wp-content/uploads/2017/01/Mylar_Chemical_Properties.pdf http://usa.dupontteijinfilms.com/wp-content/uploads/2017/01/... See Figure 2, Gas Permeability of Mylar vs. Temperature Helium permeates Mylar significantly faster than hydrogen over the full temperature range tested. It looks like the helium permeation rate is nearly double that of hydrogen near room temperature. Surprising! I would have guessed that lighter gases permeate faster. Note on the same figure that oxygen permeates faster than nitrogen even though it's heavier. There is more tabular data here: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19690004779.pdf https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/196900... It confirms the same trend. Helium permeates Mylar faster than hydrogen.
- Rerarom 8y agoWhat about helium?
- gnode 8y agoHelium is expensive and practically non-renewable on Earth. It forms slowly by beta decay, with most of it escaping into space (because it's molecular mass is so low, its velocity commonly exceeds Earth's escape velocity). A small amount gets trapped in deposits which we can extract.
- salawat 7y agoHydrogen will have issues supply-wise if we kick into industrial scale processes with high loss rates without some way to ensure the gas recombines with Oxygen to precipitate as water again. Which at the operating heights being suggested, would be problematic. Furthermore, what about all that waste Oxygen from Hydrolysis? We already run into issues with water without cracking water vapor and venting hydrogen into the atmosphere at scale. I shudder at the thought of unconstrained industry being cut loose with the idea that we have an essentially limitless supply without sitting down to really figure out the numbers. Never mind the maintenance issues. High levels of electrical generation/storage +volatile gas generator? What could possibly go wrong? Hydrogen embrittlement, high level of oxidative stress, increased radiation exposure... Mean-time-to-failure is not giving the magic 8 ball warm fuzzies. Could be super neat for meteorological/astronomical purposes/reconnaissance purposes though. I can see the international incidents rolling in now. "North Korea protests American Weather Baloons" "Russia introduces new anti-balloon laser" "China threatens Taiwan over balloon based infrastructure" Unfortunately, I wouldn't put it passed ad companies to utilize this "exciting new breakthrough in audience outreach" as well. I'd really like to look at this kind of stuff how I used to as a kid again. Too much time in the tech industry has absolutely ruined my outlook however.
- gnode 7y agoI'm not exactly sure what it is you're decrying. That we'll lose a significant quantity of Earth's hydrogen to space, leaving the atmosphere with too much oxygen? That we'll suffer a water shortage because we're using too much of it to make hydrogen? That nations will increasingly ignore other nations' aerospace sovereignty because balloons are filled with hydrogen instead of helium? Hydrogen is still expensive to split from water, and the quantities required for deleterious effects to present are so high, that these are really distantly hypothetical "what ifs".
- deleted 8y ago[deleted]
- logfromblammo 8y agoMake a vacuum onion. 1d-compressium, 1d-tensilium, and 2d-tensilium are all allotropes of obtainium, being the materials with the highest uniaxial compressive strength to mass ratio, the highest uniaxial tensile strength to mass ratio, and the highest biaxial tensile/shear strength to mass ratio. Currently, those are probably diamond struts, buckytube fiber cables, and graphene sheets. Throw 2d-tensilium envelope around a tensegrity frame with 1d-compressium struts and 1d-tensilium cables. Pump out the interior gas until it breaches or collapses. Start over. This time, put another frame and envelope around the first, and anchor them to each other with more 1d-tensilium cables. Pump out the interior gas of both pockets until the outer shell breaches or collapses. Repeat, until the pressure differential on every envelope and shell is insufficient to breach the envelope or buckle the frame. Now you have a gradient from vacuum to atmospheric pressure instead of a perfect vacuum in the whole volume, but you don't have to find any unobtainium to build it. As a bonus, you can put the envelope on the inside of the shells, and follow a similar process of breaking each one with air, to make an inflatable spacecraft hull that can hold 1 atm of breathing gas on the inside without rupturing in vacuum, using minimal mass.
- lnanek2 7y agoWouldn't all that inner material be too heavy to float after that?
- logfromblammo 7y agoYou have to make the shell large. The bigger it is, the more slack you can get with the strength of materials and vacuum pump power.
- upofadown 7y agoVacuum only gets you 7% more lifting force over hydrogen: * https://en.wikipedia.org/wiki/Vacuum_airship#Principle https://en.wikipedia.org/wiki/Vacuum_airship#Principle