The first-ever manned airplane that can fly by day or night on solar power alone landed in the dark at a major southwestern US airport, a live feed from the organizer's website showed early Saturday.
Solar Impulse, piloted by Swiss adventurer Bertrand Piccard, touched down at the Sky Harbor International Airport in Phoenix, Arizona at 0730 GMT after departing from California more than 18 hours earlier on the first leg of a cross-country journey.
A ground crew met the plane as it landed and pushed it to a safe area where Solar Impulse co-founder Andre Borschberg, a Swiss engineer and ex-fighter pilot, climbed up to the cockpit on a ladder to greet Piccard, who raised his arms in triumph.
"I'm happy to be here, happy to have landed in Phoenix," a visibly elated Piccard told reporters, as a small crowd assembled on the tarmac cheered his arrival.
Piccard said he was impressed by the scenery as he overflew the southwestern United States, first over California then over the Arizona desert and his nighttime approach to Phoenix. When he landed he said he still had three-quarters of his battery power left.
The US journey is being billed as the plane's first cross-continent flight.
The plane, which has a slim body and four electric engines attached to an enormous wingspan, flew quietly at an average speed of about 30 miles (49 kilometers) per hour. Energy provided by 12,000 solar cells powered the plane's propellers.
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 can fly at night by reaching a high elevation of 27,000 feet (8,230 meters) 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 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 Piccard and Borschberg to share duties and rest between flights.
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, were online at live.solarimpulse.com.
The aircraft completed its first intercontinental journey from Europe to Africa in June on a jaunt from Madrid to Rabat.
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 the stops.
Solar Impulse was launched in 2003.
The slim plane is particularly sensitive to turbulence and has no room for passengers, but Piccard has insisted that those issues are challenges to be met in the future, rather than setbacks.
"Instead of speaking of the problems, we want to demonstrate solutions," Piccard said earlier as he was flying toward Phoenix, stressing that renewable technologies already exist and are well known to science.
"Now we need to put them on a big scale everywhere in our daily life."