US Navy drone flies two days straight using liquid hydrogen tank

As the US military discovers just how useful drones can be, it's eager to keep them flying as long as can be, and the US Office of Naval Research now has a drone that can fly for two whole days. The Ion Tiger, an experimental surveillance plane that uses a hydrogen fuel cell as its power source, flew for a record 26 hours using pressurized hydrogen back in 2009, but late last month it managed a full 48 hours and one minute thanks to a new cryogenic storage tank filled with liquid hydrogen. That'...