Marcus Scherdel and Solar Impulse

The spirit of the early aviators lives on in projects like the experimental Solar Impulse, a solar-powered plane that made its initial, barely-off-the-ground test flight in December 2009. Here, pilot Marcus Scherdel converses from the cockpit of the aircraft--which has the wingspan of a 747 but the weight of a midsize car--before heading down the runway.

A more ambitious nighttime flight, drawing on batteries that have been charged during daylight hours, is expected sometime this summer.

As ambitious as the project is, Solar Impulse founder Bertrand Piccard see it as more than just about aeronautics. "If an aircraft is able to fly day and night without fuel, propelled solely by solar energy, let no one come and claim that is impossible to do the same thing for motor vehicles, heating and air conditioning systems, and computers," he said in June 2009 when the aircraft made its public debut.