It isn’t the fastest plane, and it carries virtually no payload save its single pilot.  What makes the Solar Impulse remarkable is that it carries no fuel, and doesn’t need any – it’s powered only by the sun.  It took off this morning from Moffet Field on the edge of San Francisco Bay at first light, about 6:12AM Pacific time  (13:12 GMT).  It should take about 19 hours to complete the first leg of the American crossing to Phoenix, Arizona, and will stop in Phoenix, Dallas, St Louis, Washington DC and New York in the coming weeks.  This marks the first time an attempt has ever been made to do something like this in an unfueled aircraft.

The aircraft, officially designated as the HB-SAI,  is being piloted by two Swiss pilots, Bertrand Piccard and Andre Borschberg.  Both pilots have racked up an impressive list of world records, The first night flight of a solar-powered craft in 2010 was followed by a first international flight in 2011, and first inter-continental flight in 2012.  Piccard is perhaps best known for being the first to circumnavigate the globe in a hot air balloon in 1999.

 

This isn’t to say that the Solar Impulse hasn’t got other ways of getting around the propulsion problem – it does. The craft’s wings and stabiliser are covered with almost 12,000 solar cells, making up about 200 square meters of solar collection surfaces.  These charge an array of lithium-ion batteries by day; the batteries, in turn, power the plane’s four electric motors, and allow the plane to be flown at night as well.  The batteries are carried in pods hanging below the enormous wings. The Solar Impulse has a 208 ft. wingspan (63 meters) that matches that of an A340 Airbus.  Despite this, its carbon fiber and honeycomb laminate construction gives it a weight of only 1.6 tons, or about as much as an average sport utility vehicle. Because all the engineering went into making it fly under solar power alone, it’s not the speediest of craft – the total output of the four electric motors is about the equivalent of a Vespa motor scooter.

The craft has been making test flights over the San Francisco area for weeks, and has already made a day-and-night flight lasting more than 26 hours.  The team aims to eventually circumnavigate the globe in 2015.

The launch on Friday is to serve as the start of the pair’s Clean Generation Initiative, an effort to encourage policy-makers and businesses to develop and adopt sustainable energy technologies.

“We want to show that with clean technologies, a passionate team and a far-reaching pioneering vision, one can achieve the impossible,” Dr Piccard said at the announcement of the mission in March.

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