The first-ever manned airplane that can fly by day or night on the Sun's power alone took off Friday on the first leg of a trip across the United States.
Solar Impulse, piloted by Swiss adventurer Bertrand Piccard, left the runway in northern California at 6:12 am (13:12 GMT) against the backdrop of a golden morning sunrise, in what a mission control operator called a "perfect takeoff."
Flying quietly and slowly at a speed of about 43 miles (70 kilometers) per hour, the plane is scheduled to arrive in Phoenix, Arizona, early Saturday under cover of darkness.
"I have almost no wind," a smiling Piccard said just over an hour into the flight.
A dashboard showing the live speed, direction, battery status, solar generator and engine power, along with cockpit cameras of both Piccard and his view from the plane, are online at live.solarimpulse.com.
The US itinerary allows for up to 10 days at each stop in order to showcase the plane's technology to the public. Other stops are planned for Dallas, Texas, and the US capital Washington, before wrapping up in New York in early July.
That will allow two pilots -- Piccard and his co-founder, Swiss engineer and ex-fighter pilot Andre Borschberg -- to share duties and rest between flights.
The project aims to showcase what can be accomplished without fossil fuels, and has set its "ultimate goal" as an around-the-world flight in 2015.
The plane has four electric motors and runs on energy provided by 12,000 solar cells.
Longer trips have already been successfully completed by the plane, which made the world's first solar 26-hour day and night trip in 2010.
However, the cockpit has room for just one pilot, so even though the plane could likely make the entire US journey in three days, Piccard decided it would be easier to rest and exchange flight control with Borschberg at rest stops.
Solar Impulse was launched in 2003. The project's ultimate goal is to fly around the world, with that endeavor scheduled for 2015.
The plane can fly at night by reaching a high elevation of 27,000 feet and then gently gliding downward, using almost no power through the night until the Sun comes up to begin recharging the aircraft's solar cells.
The US journey is being billed as the plane's first cross-continent flight. The plane completed its first intercontinental journey from Europe to Africa in June 2012 on a jaunt from Madrid to Rabat.
The slim plane is particularly sensitive to turbulence and has no room for passengers, but Piccard has insisted that those issues are not setbacks but challenges to be met in the future.
The project is designed to push the boundaries of what is possible in aviation by using renewable energy instead of fossil fuels.
"Our airplane is not designed to carry passengers, but to carry a message," Piccard has said.