Titan Aerospace has unveiled the Solara 50 and Solara 60, two high-altitude solar-powered UAVs the company is calling “atmospheric satellites”. The aircraft are designed to fly up to 65,000ft (19,800m) altitude and remain there for up to weeks at a time, sustained by a 50m wingspan and a single large battery-powered propeller, itself powered by thousands of high-efficiency solar cells placed on virtually every possible surface. It is not the first multi-week “atmospheric satellite” aircraft. The Defense Advanced Research Projects Agency (DARPA) initiated a programme to develop just such a concept, resulting in AeroVironment’s Global Observer, which was unfortunately destroyed in a crash, and QinetiQ’s Zephyr, a demonstrator design for Boeing‘s Vulture concept. Though the Solara programme is unrelated, the programmes all share similar characteristics – multi-year endurance and a 65,000ft operating altitude. Between 60,000-70,000ft sits a “sweet spot”, says Titan, where the average winds are less than 5kts.