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Sunny finale to Solar Impulse's night flight

Soaring in the sky for more than 26 hours, a slender, lightweight plane completes a historic overnight flight powered purely by solar energy.

Powered by the sun, the Solar Impulse stays aloft for 26 hours.
Powered by the sun, the Solar Impulse stayed in the air for 26 hours. Solar Impulse/Stephane Gros

Energized just by the rays of the sun, the Solar Impulse HB-SIA aircraft landed Thursday morning at its Swiss airbase after completing its first day-and-night flight.

Kept aloft for more than 26 hours by pilot André Borschberg, the lightweight, long-limbed solar plane made it into the history books by achieving the longest and highest flight in the history of solar aviation, according to the Solar Impulse team. Greeted by hundreds of cheering supporters upon landing at 9:00 a.m. Swiss time, Borschberg expressed his feelings about the historic journey.

"I've been a pilot for 40 years now, but this flight has been the most incredible one of my flying career," said Borschberg, also the CEO and co-founder of the project, as he exited the cockpit. "Just sitting there and watching the battery charge level rise and rise thanks to the sun... And then that suspense, not knowing whether we were going to manage to stay up in the air the whole night. And finally the joy of seeing the sun rise and feeling the energy beginning to circulate in the solar panels again!"

As the sun set, the Solar Impulse stayed in the sky, powered solely by its charged batteries.
As the sun set, the Solar Impulse stayed in the sky, powered solely by its chargec batteries. Solar Impulse/Stephane Gros

To complete the flight, Borschberg slowly attained an altitude of 28,000 feet on Wednesday as the energy from the sun powered the Solar Impulse HB-SIA and charged its batteries to keep it aloft at night. As the sun set, the pilot switched to those batteries hoping they would provide enough power to stay in the sky the entire night.

In the hours of darkness, the aircraft flew "on pure potential energy," the Solar Impulse team wrote, "meaning no direct solar power from the sun, no indirect solar power from the batteries, but simply lift from a slow descent."

The HB-SIA's solar panels, with more than 12,000 solar cells, are on its wings, which stretch as far as those on a 747 jumbo jet. They provided the juice to the plane's lithium polymer batteries and to the four 10-horsepower electric motors that got the aircraft, which at 1.7 tons weighs only about as much as a car, off the ground.

The team was, understandably, exultant when the mission was over.

"I have just flown more than 26 hours without using a drop of fuel and without causing any pollution," added Borschberg after his landing.

Bertrand Piccard, the initiator and president of the project, also had a few happy words for his partner the moment the plane touched down.

"Bravo André! You have just proved that what I have been dreaming about for the last 11 years is possible", said Piccard. "This is a crucial step forward, it gives full credibility to the speeches [we've been giving for] years about renewable energies and clean techs and allows us now to get closer to the perpetual flight without using a drop of fuel!"

For the record, the stats for the flight were as follows:

  • Take-off time: 7/7/2010 - 6:51 a.m
  • Landing time: 7/8/2010 - 9:00 a.m.
  • Flight duration: 26 hours, 9 minutes, 26 seconds.
  • Maximum speed: 68 knots (78 mph) (ground speed).
  • Average speed: 23 knots (26 mph).
  • Maximum altitude: 28,000 feet above sea level.

The flight seems to have been accomplished without undue stress. At about midnight Switzerland time, the Solar Impulse blog offered this report: "André says he's feeling great up there...Everything has been going well. His only complaints involve little things like a slightly sore back, as well as a 10-hour period during which it was -20 degrees Celsius in the cockpit. That made his drinking water system freeze up and worse of all, his ipod batteries die."

A Web site set up for the night flight maps out the plane's journey and will eventually offer a recording of the landing.

The success of HB-SIA prototype this week paves the way for the next journey of the Solar Impulse. Now that the plane has proven it can fly at night using solar energy captured during the day, the team said it plans to push the human and technological limits further. Next will be a flight across the Atlantic (in 2011) and then an around-the-world trip (in 2012) using the HB-SIB prototype set to be built this summer.