Ground crew prepares the Solar Impulse plane early in the morning before taking off to embark on a multi-city trip across the United States from Moffett Field NASA Ames Research Center in Mountain View, Calif., Friday. — AP photo

Laila Kearney

SAN FRANCISCO — A solar-powered airplane that developers hope to eventually pilot around the world took off early on Friday from San Francisco Bay on the first leg of an attempt to fly across the United States with no fuel but the sun’s energy.



The spindly looking plane, dubbed the Solar Impulse, departed shortly after 6 a.m. local time from Moffett Field, a joint civil-military airport near the south end of San Francisco, heading first to Phoenix on a slow-speed flight expected to take 19 hours.



After additional stops in Dallas, St. Louis and Washington, D.C., with pauses at each destination to wait for favorable weather, the flight team hopes to conclude the plane’s cross-country voyage in about two months at John F. Kennedy International Airport in New York.



Swiss pilots and co-founders of the project, Bertrand Piccard and Andre Borschberg, will take turns flying the plane, built with a single-seat cockpit, with Piccard at the controls for the first flight to Arizona. He is scheduled to land in Phoenix at 1 a.m. local time on Saturday.



The project began in 2003 with a 10-year budget of 90 million euros ($112 million) and has involved engineers from Swiss escalator maker Schindler and research aid from Belgian chemicals group Solvay — backers who want to test new materials and technologies while also gaining brand recognition.

With the wingspan of a jumbo jet and weighing the same as a small car, the Solar Impulse is a test model for a more advanced aircraft the team plans to build to circumnavigate the globe in 2015. The plane made its first intercontinental flight, from Spain to Morocco, last June.



The aircraft runs on about the same power as a motor scooter, propelled by energy collected from 12,000 solar cells built into the wings that simultaneously recharge batteries with a storage capacity equivalent to a Tesla electric car.



In that way, the Solar Impulse can fly after dark on solar energy generated during daylight hours, and will become the first solar-powered aircraft capable of operating day and night without fuel to attempt a US coast-to-coast flight.



But the plane is unlikely to set any speed or altitude records. It can climb gradually to 28,000 feet (8,500 meters) and flies at an average pace of just 43 miles per hour (69 km per hour).



A ground team of weather specialists, air traffic controllers and engineers track the plane’s speed and battery levels and help the pilot steer clear of turbulence. Solar Impulse cannot fly in strong wind, fog, rain or clouds. Its machinery is not even designed to withstand moisture.— Reuters