A solar-powered aircraft was scheduled to be launched from California to New York on May 4 on a flight across the United States, aiming to showcase what is possible without fossil fuels. The experimental Solar Impulse plane -- with the wingspan of a Boeing 747 but the weight of a small car -- bears 12,000 solar cells.    

By day, the cells power the plane's electric motors while also charging batteries, so the plane, unlike other solar aircraft, can keep flying all night. The project was launched over a decade ago, after inveterate adventurer Bertrand Piccard, 54, nearly ran out of fuel on his historic non-stop round-the-world balloon flight. The Swiss psychiatrist decided to re-attempt the journey    

Solar Impulse aims to launch a long flight, without using any fossil fuel. Adventure in the 21st century consists in using human creativity and the pioneering spirit to develop the quality of life to which present and future generations are entitled, he said in a statement, explaining his philosophy.    

The Solar Impulse plane has already made several trips, including a 26-hour flight in 2010, but this is its first trip across a continent. The plane could make the flight nonstop -- it would take approximately three days, travelling at the aircraft's cruising speed of around 70 kilometre per hour, its creators said.    

But with space for only one pilot and the intensive task of navigating the ultra-light but ultra-long plane through turbulence, Solar Impulse decided, for safety reasons, to break the flight up into multiple stages. That will allow two pilots -- Piccard and his co-founder, Swiss engineer and ex-fighter pilot Andre Borschberg -- to share duties and rest between legs.    

The plane is scheduled to stay over in Phoenix, Dallas and Washington, DC. Before arriving in New York in early July. It will spend up to 10 days at each stop on its journey in order to showcase its technology to the public, schoolchildren and students who will also have a chance to talk with the pilots.