By now you know the theme - US defense research agency Darpa wants an unmanned aircraft that can stay aloft for five years. In previous posts we've seen Aurora's three UAVs take off and join up to form one massive stratospheric pseudo-satellite. And we've seen Boeing's steroidal version of Qinetiq's Zephyr solar-electric UAV. Now it's Skunk Works' turn.

Photo: Lockheed Martin

Like the Aurora and Boeing concepts selected for study under Darpa's Vulture program, Lockheed's UAV is solar-powered. Like Boeing's, but unlike Aurora's, it is a single vehicle intended to stay aloft for the full five years. Notable design features include the tails, which rotate to collect the most sunlight. The "launch once" vehicle will also capture photovoltaic energy from the Earth's albedo, says Derek Bye, Lockheed's Vulture program manager.

The gondolas distribute systems and payload weight along the 300ft-plus span and are connected by a lower strut that helps stabilise the lightweight, flexible structure. The engines are electric ring motors, which avoid the need for gearboxes by driving the propellers directly at a distance from the hub. Bye says the Skunk Works is drawing on the satellite experience of Lockheed Space Systems business to design the ultra-reliable vehicle.