Beginning in May, Piccard and a partner will take turns flying a single-seat, solar-powered airplane from San Francisco to New York—a prelude to an around-the-world flight planned for 2015. Named HB-SIA (for Solar Impulse Alpha), Piccard’s plane defies conventional aviation wisdom. When he first told others about his dream, “almost everybody thought I was completely crazy,” he says. Although pioneers like Paul MacCready had been building manned solar-powered aircraft since the 1970s, none were capable of flying after the sun had set, let alone across the Atlantic and Pacific for days at a time.
The obstacle is weight. To fly through the night, a plane must draw upon power from batteries charged during the day. But batteries hold far less energy per pound than a tank of jet fuel, so a plane must carry more weight in batteries to travel an equivalent distance. A heavier plane needs more energy to fly, which in turn requires even more battery power. Add a cockpit and pilot and the craft could be too heavy to even take off. That’s why solar-powered aircraft research has typically focused on unmanned vehicles, such as NASA’s flying-wing Helios.