The highest-endurance aircraft currently flying is Northrop Grummans Global Hawk UAV, which can stay aloft for up to 40 hours. Now Darpa—which, to its credit, is never short on outlandish ideas—wants to beat that endurance record more than 1,000 times. The goal of Darpa's recently launched Vulture Program is to build a kind of atmospheric satellite that can stay aloft for five years at a time with little or no maintenance.