An airplane entirely powered by the sun landed in Washington on Sunday after a flight from St. Louis, the next-to-last leg of a journey across the United States intended to boost support for clean energy technologies. _0"> The Solar Impulse landed at Dulles International Airport outside Washington at 12:15 a.m. EDT, organizers said in a statement. It will remain in the U.S. capital until it takes off for New York in early July for the last leg of its historic trip. If the spindly experimental aircraft completes the journey as planned, it will be the first solar-powered plane capable of operating day and night to fly across the United States. "It proves the reliability and potential of clean technologies, and this is crucial in pushing our message forward," Swiss pilot Bertrand Piccard said in the statement. Piccard founded the Solar Impulse project with fellow pilot Andre Borschberg. With the wingspan of a jumbo jet and the weight of a small car, the Solar Imp