IIRC, hydrogen would be much cheaper and is lighter. The only thing stopping its use in the US is archaic law/regulation by the FAA that was put in place in the

IIRC, hydrogen would be much cheaper and is lighter. The only thing stopping its use in the US is archaic law/regulation by the FAA that was put in place in the wake of the Hindenburg disaster. Hydrogen doesn't burn without oxygen, and modern designs eliminate the risk of a leak that would result in a highly flammable gas mixture. Being outside US airspace in this example, that wouldn't be a problem.