An experimental solar-powered aircraft took off from a Swiss airbase here in the early hours of Wednesday in a bid to make history by flying round the clock and through the night.
PAYERNE, Switzerland (AFP) – Solar Impulse whirred along the runway at Payerne in western Switzerland, reaching 35 kilometres per hour (22 mph) as lone pilot Andre Borschberg gently lifted into clear skies at 6.51 am (0451 GMT) on a scheduled 25 hour flight,
"This should be a great day of all goes well," said team chief Bertrand Piccard, who made the first non-stop round-the-world flight in a balloon more than a decade ago.
"It's clear that this is something that is completely different at least for aviation, but it's also something completely different to what has existed in our society," he added moments before take-off.
"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."
The ground control crew were due to decide about 13 hours later, shortly before dusk, whether Borschberg should press on through darkness.
The go-ahead will depend on the sun's ability to charge up Solar Impulse's batteries in the daytime and the threat of strong high altitude winds, joint flight control chief and former astronaut Claude Nicollier said.
"We're confident the plane can do it," he added.
The round-the-clock flight by the prototype built last year is the first major hurdle for the project since it started seven years ago, with the aim of flying around the world by 2013 or 2014.
A first attempt was called off an hour before scheduled take off last Thursday after an electronic component failed, but it was replaced within days.
The single seater shaped like a giant dragonfly is clad with solar panels across a wingspan the size of an Airbus A340 airliner.
But the high tech craft is powered by just four small electric motors -- as the crew put it, the "power of a scooter" -- and weighs little more than a saloon car, saving even on an automatic pilot.
Borschberg, a former fighter jet pilot, has to stay alert for the whole flight with the help of space mission-like ground control team.
Solar Impulse has completed at least 10 test flights since it first hopped along a runway seven months ago, staying aloft for up to 14 hours in the long summer daylight hours.
But the ultimate test will be to fly on through darkness and land back at Payerne shortly after dawn on Thursday having been fuelled by nothing but the sun's rays.
The pioneering bid is being monitored by the international aeronautical federation (FIA), which oversees aviation records.