garymortimer writes with news of the test flight of a hydrogen powered UAV. From the article: "Phantom Eye's innovative and environmentally responsible liquid-hydrogen propulsion system will allow the aircraft to stay on station for up to four days while providing persistent monitoring over large areas at a ceiling of up to 65,000 feet, creating only water as a byproduct. The demonstrator, with its 150-foot wingspan, is capable of carrying a 450-pound payload."