What goes up, must come down … eventually. That’s the principle U.S. military research agency DARPA wanted to stretch to its limit when it dreamed up the Vulture project, an unmanned spy plane that could stay aloft for five years. Last year, it challenged aircraft designers to come up with a plan that could keep a half-ton payload flying for a long, long time, and now the research group is said to be close to awarding a contract to build such a plane.

It’s still a mystery how the craft will loiter around up there at its prescribed 60,000 to 90,000-foot altitude for so long, but since DARPA has ruled out radioactive fuel, it must have something to do with fuel cells, solar energy, or a combination of the two. Or maybe it just stays in the air via pure magic. NASA, the originator of the graphic above, could have something to do with the technology that will accomplish this feat, but DARPA's not naming any partners just yet.

Flight magazine, via C|NET News