Solar Impulse – Solar Impulse, a Swiss-made, solar-powered aircraft, soars above San Francisco's Golden Gate Bridge in April. The one-of-a-kind aircraft is on a five-leg voyage across the United States.
In the cockpit – Bertrand Piccard, one of two pilots who take turns flying the Solar Impulse, comes from a family of adventurers. In 1999, Piccard was part of a two-man team that became the world's first to circle the globe in a balloon.
On the ground – When Solar Impulse is on the ground, it requires a carefully orchestrated landing crew to make sure it remains in proper position.
Solar cells – The plane's silicon solar cells are built into the forward and rear wings, rather than glued on. They number nearly 12,000.
Slow but steady – The aircraft's cruising speed is about 43 mph. Its maximum cruising altitude is about 28,000 feet.
Night flying – Solar Impulse, lit with more than a dozen solar-powered lights, touches down at Phoenix Sky Harbor Airport on May 3. It's the first aircraft to fly for 24 continuous hours only on sun power.
Celebration – Solar Impulse co-pilots Andre Borschberg, left, and Piccard celebrate completion of the first leg of their American mission on May 3.
Sunseeker I: First solar plane to cross the U.S. – In 1990, Eric Raymond's Sunseeker I became the first solar-powered aircraft to cross the United States. He completed the journey in 21 segments.
Paris – The Solar Impulse soars high above the streets of Paris in 2012.
Pre-flight – Betrand Piccard prepares for takeoff.
Wide and lightweight – The wings of Solar Impulse measure more than 200 feet from wingtip to wingtip. That's longer than the width of a Boeing 747 Jumbo Jet. Yet the plane weighs only about 3,500 pounds -- about the same as a Honda CR-V.
Co-pilots – Bertrand Piccard (left) and Andre Borschberg pose beside the aircraft.
Dreams of circumnavigation – An attempt to fly around the world is planned for 2015.