Here is a video showing compilation of test flights of the solar-powered, remotely piloted NASA’s Helios aircraft.
Helios set out from Kauai in the Hawaiian Islands before 9:00 AM on Monday, August 13, 2001. Just over seven hours later, it reached 96,500 feet. Flying at about 25 miles an hour, the mission lasted nearly 17 hours, landing at 1:43 a.m. August 14, 2001
This was the first time a non-rocket powered aircraft has maintained flight this far above the earth. At this altitude above ground the sky is almost black, stars shine in the daytime, and the horizon looks curved.
Helios was an ultralight flying wing built by AeroVironment Inc, as a part of NASA’s Environmental Research Aircraft and Sensor Technology (ERAST) project. Covered with solar cells, Helios’ impressive 247 foot wide wing exceeds the wing span and even overall length of a Boeing 747 jet airliner.
Helios had about 62,000 solar cells across the wing. The solar cells collect energy from the Sun and convert it to electricity, which runs the 14 small motors. The motors turn the 14 propellers, which are specially designed to pull the aircraft aloft even in the very thin air that’s 18 miles high.
Helios was intended as a technology demonstrator, but in the extremely thin air 100,000 feet above Earth’s surface, the flight of Helios also approached conditions for winged flight in the atmosphere of Mars, since the atmosphere at that height above earth replicates the atmosphere near the Martian surface.