The linked articles from the 1887 New York Times are wonderful:<p>"The means by which passengers will be landed en route is also in doubt. Some suggest that they will simply be dropped overboard and their luggage thrown after them, while others maintain that a coil of greased rope for the purposes of descent will be carried on each and every machine."<p>Truly the Hyperloop of its day.<p><a href="http://query.nytimes.com/mem/archive-free/pdf?res=9904E7D81538E533A25757C1A9649C94669FD7CF" rel="nofollow">http://query.nytimes.com/mem/archive-free/pdf?res=9904E7D815...</a>
At atmospheric pressure, a given volume of hydrogen weighs approximately 7% (there is some variation with temperature) of an equivalent volume of air. All that is needed to contain hydrogen at atmospheric pressure is a membrane it can't pass through. The inwards force exerted on the membrane by the atmosphere is perfectly balanced by the outwards force exerted by the hydrogen gas. The only structural material required is for the purpose of harnessing the lifting power of the enclosed gas, providing an aerodynamic shape, etc..<p>Conversely, a vessel containing a vacuum must be built to withstand the 101,325 N/m^2 net inward force exerted upon it by the atmosphere that is not balanced by the outward pressure of the contents of the vessel. Consider, for a moment, what you would need to build a 1 m^2 coffee table out of if 20 elephants were to be able to stand on top of it at once.<p>For the sake of argument, let's say that we had a magical material that would let us build a replica of the Hindenburg that is of equal weight to the original, only with vacuum vessels replacing the hydrogen bags. The Hindenberg contained 200,000 m^3 of hydrogen lift gas, weighing 1,798 kg and displacing enough atmosphere to provide a total lift of 25,850 kg, 10,000 kg of which were considered it's cargo capacity beyond the passengers it carried. This new version of the Hindenberg, despite being built with materials and techniques that are probably well beyond our current level of technology, would carry the same number of passengers and just 18% more cargo.<p>For those of you who think that vacuum vessels are a lot safer than hydrogen, I'd like to remind you that the atmosphere surrounding 200,000 m^3 of vacuum provides a rather huge amount of potential energy waiting to be released. When vacuum vessels of a large size fail the resulting implosion can be both spectacular and devastating.<p><a href="https://www.youtube.com/watch?v=Zz95_VvTxZM" rel="nofollow">https://www.youtube.com/watch?v=Zz95_VvTxZM</a>
I have wondered if such a thing could be designed for use in the upper atmosphere and dropped in from space. That would avoid the need to keep out the full atmosphere. But then so would pumping out the air as it gained altitude...
This is an idea that seems interesting at first glance, but it's really not. What's important for lift isn't the absolute weight of the gas; it's the ratio of the weight of the lifting gas to the surrounding air. What that means is while hydrogen gives you about 1kg/m3 lift a perfect vacuum bottle only gives you about 1.3kg/m3. It probably wouldn't make sense even if we had the necessary exotic materials.
The major weakness of a vacuum airship is that a breach of the pressure hull will compromise the vacuum and thus the buoyancy. So any truly useful solution will require a number of independent vacuum cells.<p>The strongest shape made of compressive members is a tetrahedron, if surfaced with an impermeable and inelastic membrane an evacuated aerostat could end up looking like <a href="http://www.theatlantic.com/video/archive/2012/01/a-gorgeous-floating-crystal-inspired-by-alexander-graham-bells-kites/251224/" rel="nofollow">http://www.theatlantic.com/video/archive/2012/01/a-gorgeous-...</a>
Misses the point hydrogen is safer, easier, could be done today with existing tech for commercial travel (Already used a lot for scientific balloons) and pretty much has the same lifting power.<p>(Also Helium is obviously currently is used in airships commercially with no real problems on top of a theoretical vacuum ship other than perhaps cost of balloon contents, which I'd guess is not the limiting factor anyway)
This rail-bound tank was probably not designed with weight savings as a prime considerations. <a href="https://www.youtube.com/watch?v=Zz95_VvTxZM" rel="nofollow">https://www.youtube.com/watch?v=Zz95_VvTxZM</a><p>Still, this is a fascinating idea and I would love to see someone make a serious attempt at it.
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.<p>Once you reach scales of 10,000 kilograms you'll be dealing with keeping 400,000 kilograms of weight out of your vacuum.
Reminds me of an idea I had for lighter than air packing material. It was going to be something like over-sized bubble wrap filled with helium, or balloons you'd insert into the spaces and inflate with a helium canister. Seems a great idea at first, but then you do the maths, and think about the materials. Unfortunately the weight savings are likely to be so minimal they're unlikely to save on postage costs, and even if they did reduce postage they're likely to be outweighed by the cost of materials. Plus you later find out that lots of other people have had the same idea and posted on the internet about it.
This reminds me of Buckminster Fuller's cloud 9 concept. His idea was that since volume scales so much more strongly than surface area for a sphere, if you make a larger and larger sphere you will enclose cubed more air for only squared more structure. Build a large enough sphere and heat the enclosed air a couple degrees above ambient and the entire structure would be buoyant, like a soap bubble with human breath in it.<p><a href="http://en.wikipedia.org/wiki/Cloud_Nine_%28tensegrity_sphere%29" rel="nofollow">http://en.wikipedia.org/wiki/Cloud_Nine_%28tensegrity_sphere...</a>
These are fun (also in Diamond Age I believe) and I like how they are both impossible to create and there is a patent application on them :-)<p>It is interesting to run the structure density vs the vacuum numbers. I always wondered if we would be able to make vacuum filled bucky balls out of carbon at some point.
Does the vacuum have to be perfect? Maybe you can reduce the pressure on the surfaces, and therefore simplify the engineering, by leaving some air in there. I think it is an interesting idea that varying the internal pressure would change your lift. You only ever need "just enough" lift anyhow.
"His patent application was eventually denied on the basis that it was 'wholly theoretical, everything being based upon calculation and nothing upon trial or demonstration.'"<p>He'd get that patent today. Little as it might avail him.