A plane that can fly on solar power, day or night, will make its way across the United States this summer - the first time the plane has attempted a cross-continental flight.
The Solar Impulse - built as a project of the Swiss Federal Institute of Technology, the brainchild of Bertrand Piccard and André Borschberg - has the wingspan of a 747 but only weighs as much a Honda Prius. It flies thanks to four turboprop engines powered entirely by batteries and solar panels.
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Borschberg told Discovery News that the although the plane could make the whole trip from California to New York in one go, the pilot cannot. The plane travels at 40 to 50 miles per hour, so a cross-country flight would take days. And since there's only room for a single person in the cockpit, in part to save weight, and no autopilot, the trip will have to be broke up into five legs.
Weight was a big part of the design constraint. The designers needed to find material that was light but also strong. They settled on carbon fiber, which is lighter than any metals.