Solar plane cruises to turning point in historic flight
An experimental solar-powered aircraft cruising above Switzerland in a historic bid to fly around the clock approached a turning point in its flight on Wednesday as night-time loomed.
Solar Impulse's mission control team at Payerne airbase in western Switzerland was due to decide shortly before sunset whether to carry on with the pioneering attempt to fly through darkness or order the pilot to land.
"The suspense is still high but we're confident," said team chief Bertrand Piccard as pilot Andre Borschberg approached 8,000 metres (52,800 feet) about 10 hours into the flight.
Solar Impulse's batteries looked set to be at full charge at full altitude, a key target as the team sets out to demonstrate the value of solar energy.
"The day challenge seems to be reached, we still have the night challenge," Piccard told journalists.
The prototype relies on the sun to power the four electric motors and charge the batteries, in theory storing enough energy to last through some seven to eight hours of darkness and land with a boost of sunlight after dawn.
Three factors were due to come into play, including the threat of thunderstorms or wind, oxygen levels on board and the state of the batteries, as well as pilot Borschberg's ability to stay alert.
"If we know that batteries were not full at the end of the climb, then we know it will not be possible to go through the night," Piccard explained.
But the team's weathermen had signalled through the day that conditions were improving to near perfection, while Borschberg appeared to be enjoying himself up in the air.
"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.
"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," he added.
Borschberg, confined to his seat in the narrow cockpit, snacked on high energy bars, home made sandwiches, French rice pudding (riz au lait) and coffee, Piccard told AFP.
The 57-year-old 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.
His bodily functions and the plane's technical parameters were also monitored second-by-second from the ground.
The single seater shaped like a giant dragonfly is clad with solar panels across a wingspan the size of an Airbus A340 airliner (63 metres), and can change direction substantially with a touch of the controls, pilots said.
The 12,000 solar cells and nearly half a tonne of batteries power four small electric motors and propellors - as the crew put it, the "power of a scooter" - and weighs little more than a saloon car.
"All is uneventful," was the word from mission control.
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.
After reaching its apogee of 8,500 metres at sundown, Solar Impulse was expected to make a slow night-time descent.
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.
The pioneering bid is being monitored by the international aeronautical federation (FIA), which oversees aviation records.
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