Cargo airships could be big
Great analysis.<p>A few random thoughts<p>1. The dreaded helium leakage. It might not be a problem at all. Think of a party balloon of the foil type. It stays afloat for weeks. And it has positive pressure. A neutral pressure one would leak much less. But maybe not to zero. Ok, now use a double layer. Just like there are double hull submarines, this would be a double foil balloon. The distance between the outer foil and the inner foil would be only 1cm or so, so 99.9999% of the helium would be inside the inner foil. The gas between the two foils would in time become mixed with air, but the amount of double leakage would be negligible. The weight of the double foil would also be negligible compared to the overall weight of the structure.<p>2. Going up and down. Hindenburg had a cruising altitude of 200m. Up to 2000 meters or so, the air density goes down by about 1% every 100 meters. So, lowering a balloon from 200m to 0m does not mean you need to fully deflate it, only that you need to reduce its buoyancy by 2%, or add 2% ballast. For a 1100 ton airship, you need to add 22 tons of ballast. Pumping 22 tons of water 200 meters high is not easy feat. But there&#x27;s a cute shortcut: you could send only 2.5 tons of hydrogen with a hose (hydrogen is more than happy to flow up), and you burn it there. The resulting water vapor needs to be condensed, but you can probably arrange that with a small refrigeration unit that you power with the electricity from a generator powered by the said hydrogen. The current cost of hydrogen is about $5 per kilogram, so this whole affair would cost you less than $15k. It&#x27;s a rounding error when you ship 500 tons of cargo.<p>3. Fuel. Yes, it would be cool to have neutrally buoyant fuel, like a mix of methane and propane. But do you think the FAA would like that? How is that different from just having some hydrogen gas onboard, like, you know, Hindenburg? I think the most conservative design choice would be to just use plain old jet fuel.