This was Nasa's Helios aircraft. Solar powered, beautiful. Lost in 2003.

"The Helios Prototype solar-electric flying wing was one of several remotely piloted aircraft, also known as uninhabited aerial vehicles or UAVs, that were developed as technology demonstrators under the now-concluded Environmental Research Aircraft and Sensor Technology (ERAST) project. Prior to its loss in an in-flight mishap in June 2003, the Helios Prototype set a world altitude record for propeller-driven aircraft of almost 97,000 feet."
More? Here.