Boeing’s rotund new drone may be kind of cute, but it represents a big technological advance in unmanned aircraft.

The Phantom Eye flew for 66 minutes this week, its second flight ever after an original run of just over 20 minutes. The ultimate goal is for Phantom Eye to cruise the skies taking surveillance for up to four hours. But that’s not what makes the drone impressive; it’s powered by two 150 horsepower liquid hydrogen engines, which means its only byproduct is water. a

It’s first flight had a bit of a rough landing that ended up damaging the drone, but the latest flight at Edwards Air Force Base was smooth sailing. Check out the Phantom Eye in action: