PAYERNE?An experimental solar-powered aircraft took the pioneering step Wednesday of flying into the night, pressing on with an historic round-the-clock flight fuelled only by the sun's energy.
"For us all, the adventure starts," said Solar Impulse chief Bertrand Piccard as the team's mission control announced at sunset that they had decided to keep pilot Andre Borschberg flying in the darkness.
Sudden, strong winds at dusk disrupted the team's planning by pushing the plane to speeds up to 140 kilometers per hour (80 mph), eating into its time in the sun, he said at Payerne airbase in western Switzerland.
But, "The rest of the parameters are good," he said. "Which means that the team mission (control) can take the decision to go through the night."
The winds sped Borschberg towards the Alps and into potential turbulence, wiping out about an hour of extra sun-bathing to charge the plane's batteries at high altitude.
"The airplane had to eat its safety margin and start to descend one hour earlier than it could have done," said Piccard.
"So if there is one hour missing tomorrow morning, it could be that hour. That could be a crucial hour."
The prototype relies on the sun to power the four electric motors and charge the batteries, in theory storing enough energy to last through about seven to eight hours of darkness and land with a boost of sunlight after dawn.
It can also gently glide down in an emergency, Piccard said.
Borschberg was thrilled. "Conditions are really beautiful up here, I feel great," the former jet fighter pilot told AFP by radio as he cruised over the Jura hills in northern Switzerland during the day.
"I've been dreaming about this for seven years since we started the project, everybody on the team was looking forward to this very special day and I can tell you I'm really enjoying it," the 57-year-old said.
Confined to his seat in the narrow cockpit, the pilot snacked on high energy bars, homemade sandwiches, French rice pudding (riz au lait) and coffee, Piccard told AFP.
Borschberg had no automatic pilot and was in constant touch with the space-like mission control team to keep alert for what could go up to least 25 hours in the air.
He was flying at 6,500 meters (21,450 feet) as night fell, at a gentler speed of 23 knots (43 kph).
The pilot's bodily functions and the plane's technical parameters were monitored second-by-second from the ground, while vibrating sleeves in his overalls were ready to wake him if the plane tilted more than few degrees.
The single-seater, shaped like a giant dragonfly, is clad with solar panels across a wingspan the size of an Airbus A340 airliner (63 meters), and can substantially change direction with a touch of the controls, pilots said.
The 12,000 solar cells and nearly half a ton of batteries power four small electric motors and propellers -- the "power of a scooter", as the crew put it -- and weigh a little more than a saloon car.
Solar Impulse took off into clear summer skies at 6:51 am (0451 GMT) on Wednesday.
"The goal is to take to the air with no fuel. The goal is to show that we can be much more independent from fossil energy than people usually think," explained Piccard.
The overnight flight is the first major hurdle for the project since it was set up seven years ago with the aim of ocean crossings, transcontinental and round the world flights by 2013 or 2014.
A first round-the-clock attempt was called off an hour before scheduled take-off last Thursday after an electronic component failed, but the aircraft has flown for up to 14 hours straight in daylight in recent weeks.
