GENEVA - An experimental solar-powered plane whose Swiss makers hope someday to fly around the globe soared into uncharted territory yesterday - the cold, dark night.
The team of adventurers and engineers behind the Solar Impulse project are already celebrating an aviation milestone for the longest solar flight after having kept the single-seat prototype aloft for almost 15 hours.
With the goal of 24 hours of nonstop flight, the team set its sights on keeping the sleek aircraft with a 207-foot wingspan in the air until this morning.
Pilot Andre Borschberg "will stay up there as long as possible," said Bertrand Piccard, the project's co-founder.
"Hopefully he will still be in the air at sunrise tomorrow. That is the challenge."
Borschberg took off from Payerne airfield shortly before 7 a.m. yesterday, allowing the plane to soak up plenty of sunshine and fly in gentle loops over the Jura mountains west of the Swiss Alps.
As the sun set, technicians hoped the Solar Impulse's batteries, charged from the 12,000 solar cells fixed to the wings and body, would keep the four-engine plane airborne through the night. The batteries would begin charging again at dawn.
Should Borschberg or the team decide that it looks like the Solar Impulse won't make it through the night, the pilot will have the difficult task of landing the fragile aircraft before the batteries run out.
Borschberg, 57, was circling in Swiss airspace, first at 28,000 feet and then gently easing down through the night - always within gliding range of the airport, so he can land if the plane runs out of energy, Piccard said. The former Swiss fighter pilot is wearing a parachute - just in case.
The aircraft has a thin fuselage and a wingspan of a Boeing 777 passenger jet. Its top speed is only 75 mph and to be as light and efficient as possible it has no room for passengers or baggage.
Piccard, who achieved the first nonstop circumnavigation of the globe in a balloon in 1999, said the next major step will be a solar Atlantic crossing. That will be done in a second, lighter prototype, because it will involve new challenges and dangers, he said.
Although the goal is to show that emissions-free air travel is possible, the team said it doesn't see solar technology replacing conventional jet propulsion any time soon. Instead, the project is designed to test and promote energy-efficient technologies.