MISSION // PILOT A SOLAR PLANE

IN 1999, WHILE DOING THE OBLIGATORY PR prior to his circumnavigation of the earth by hot-air balloon, 47-year-old Swiss adventurer Bertrand Piccard was struck with a radical notion: "I had this idea that the purest way to fly would be with no fuel, no pollution." Thus began the planning for the Solar Impulse, a plane he hopes will make the first sun-powered round-the-world flight.

It's an audacious undertaking, considering that the most recent solar aviation milestone was a 48-hour sortie by a radio-controlled craft this past June. To pull it off, he'll need an extraordinarily efficient plane and a roller-coaster-like flight plan. The single-cockpit, 260-foot-wingspan Solar Impulse, constructed of ultralight carbon fiber, will spend its days climbing to 40,000 feet, then, surviving on 880 pounds of batteries, make slow nocturnal descents to 15,000 feet, just above the cloud layer—any lower and an overcast morning could force a crash landing.

Piccard, whose father took a submersible to the bottom of the Pacific, in 1960, has already raised $15.5 million for the concept. His timeline calls for test flights in 2008, a transcontinental run in 2009, then the four-leg roundabout—with Piccard and two other pilots switching off—in 2010. While the adventure alone is worth the effort, Piccard has a grander vision. "A solar circumnavigation sends a very important message," he says. "It's a beautiful symbol for renewable energy and the pioneering spirit of invention."