Considered the world's most advanced sun-powered plane, the Solar Impulse took off from Moffett Field in Mountain View at first light for a two-hour practice run in advance of a planned multi-city, cross-country tour.
"That's a mythical step in aviation," André Borschberg, one of the plane's pilots and creators, said about flying cross-country. "We are something like between 1915 and 1920, compared to traditional aviation, when pioneers tried these non-stop flights."
He said a flight around the world could occur in two years.
The Solar Impulse is powered by about 12,000 photovoltaic cells that cover massive wings and charge its batteries, allowing it to fly day and night without jet fuel. It has the wing span of a commercial airplane but the weight of the average family car, making it vulnerable to bad weather.
Its creators say the Solar Impulse is designed to showcase the potential of solar power and will never replace fuel-powered commercial flights. The delicate, single-seat plane cruises around 40 mph and can't fly through clouds.
Borschberg and Bertrand Piccard, Solar Impulse co-founder and chairman, said the plane should be ready for the cross-country journey on May 1, depending on the weather.
"We like nice weather. We like sunny days," Borschberg said.
Stops are planned in Phoenix, Dallas, Washington, D.C., and New York. Each flight leg will take 20 to 25 hours, with 10-day stops in each city.
Between Dallas and Washington, the plane will also stop at one of three other cities - Atlanta, Nashville or St. Louis.
Borschberg said the plane's creators are close to being able to launch the non-stop flights needed to go around the world.
Using solar power, "we are close to the notion of perpetual flight," he said.