[scoopertrooper]

Just crazy enough to work. Hydrogen doesn't autoignite till 500 degrees celsius, while your average hot air balloon only heats gas to 100 degrees.

You'd want to be damn sure about the reliability of your thermocontroller though.

[b112]

I think the fuels, and components to heat without flame, might reduce the benefit a lot.

I have often wondered about super strong materials, a sphere with vacuum inside.