The British team of engineers leading the PHASA-35 unmanned aircraft project ... have shown that the solar-powered aircraft can remain airborne for 24 hours at an altitude of over 66,000 feet.

Credit: Prismatic Prismatic, the BAE Systems-owned developer of solar-powered high-altitude pseudo-satellites, is gearing up for multiday flights with a new version of its PHASA-35 uncrewed ...