The wings of the experimental aircraft arch more than 63 metres, the same span as an Airbus A340, but they look frail, supported on the airstrip by wheeled struts. They are covered in a patina of 11,268 photovoltaic cells, which look dark blue in the grey predawn. The four 10-horsepower propellers they power now start to spin silently. Bertrand Piccard, a 55-year-old explorer and psychiatrist, dons his helmet and oxygen mask and completes his final checks. The Solar Impulse quietly taxies forwards. The plane is travelling impossibly slowly – 30km an hour – when it gently noses up and leaves the ground. With air beneath them, the rangy wings seem to gain strength; the fuselage that on the ground seemed flimsy becomes elegant, like a crane vaunting in flight. It seems not to fly, though, so much as float. Piccard spends the day wheeling the solar-powered plane around the Matterhorn and lands 12 hours later, after sunset. But the Solar Impulse is a plane that would fly for ever.
This summer, it limited itself to crossing the US. It took off from San Francisco in May and flew past the Statue of Liberty before landing at JFK in July, traversing the country in five stages, with Piccard and the other co-founder of the project, André Borschberg, a former fighter pilot in the Swiss air force, swapping places in the cockpit. The flight was a remarkable achievement: the Solar Impulse flew further than any solar-powered aircraft before. The plane that crossed America is a prototype, with the name HB-SIA. Its successor, the HB-SIB, currently being built, will try to circumnavigate the world in 2015, using about as much power as a scooter does. With no rival, it will have the skies to itself, but on land and on sea, too, a new generation of solar-powered vehicles is making extraordinary journeys, around the world and across continents.
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