How far are we from creating a aircraft, like a glider that can maintain its altitude that can fly indefinitely.
Oops, beaten by Solar Impulse, as other commenter points out.
Let's up the stakes? How long until a solar aircraft runs on another planet? NASA is talking up Mars Aerial and Ground Global Intelligent Explorer (MAGGIE). Very low atmospheric density, and 59% the solar energy. https://www.nasa.gov/general/mars-aerial-and-ground-global-i...