Earlier this month we reported on NASA's first attempt to test their solar-electric Helios UAV with a regenerative hydrogen fuel cell system for night flight. During the first flight, the Helios was aloft for 15 hours at 52,000 feet powered by it's 62,000 solar cells but the fuel cell system could not be brought online due to a coolant leak. A second flight is planned for today. The eventual goal is to develop a robot plane that can fly perpetually during night and day. For photos of the Helios including the first fuel cell test flight and previous record-setting flights, see the Dryden Helios Photo Gallery.