It must be able to haul a 1,0000-pound payload all the while, and operate at an altitude of 60,000 to 90,000 feet. How does one power a plane that's going go fly for five years? Solar seems to be the most logical option, though fuel cells could work, too. It's not clear what shape the craft could take, though the NASA ultra-endurance concept aircraft pictured here could give some hints. Darpa says it's close to awarding contracts; then phase one of the three-part program, which will focus on figuring out what this kind of plane might actually look like, can begin. Once someone has built a full-scale demonstrator that can stay in the air for 12 months, a Vulture program aircraft will enter production.