An experimental aircraft, Solar Impulse, was set to take off from a Swiss airbase early today on the first attempt to fly around the clock fuelled by nothing but the energy of the sun.
Solar Impulse is ultimately aiming for the aviator's dream of "perpetual flight" and to prove a point by flying through the night, said the venture's founder, the first balloonist to circumnavigate the globe, Bertrand Piccard.
"The great adventure of the 21st century is no longer to go to the moon, because that has already been done, it's about moving society bit by bit away from its dependence on fossil fuels," the Swiss adventurer claimed.
"Solar Impulse is a lot more than an aviation adventure, it's a demonstration of what this new technology can bring to society."
The single seater clad with solar panels, which weighs little more than a saloon car but bears the wingspan of an Airbus A340 airliner, has completed 10 test flights since it first hopped along a runway seven months ago. Packed with cutting- edge technology, the prototype's four sun-fuelled 10 horsepower electric motors have gently hauled it to high altitude, flying for hours on end.
Joint founder Andre Borschberg described a dawn flight on Tuesday as "totally cool" after a fright over the weekend when another test pilot felt vibrations as he stretched the plane to its limits.
The pioneering attempt is fraught. A 25-hour window of fine summer weather is needed from the moment the ultra lightweight plane takes off from Payerne airbase.
Former space shuttle astronaut Claude Nicollier said the most critical period would come overnight as daytime solar energy stored in batteries runs low and the team looks to the rising sun for a boost. "We'll have very little energy and will have to make a decision on whether to continue or land," the flight test chief explained.
Another challenge will be keeping Mr Borschberg alert for 24 hours.
"The plane demands a lot of attention, there's no autopilot. You can't snooze for a few minutes," Mr Nicollier pointed out.
Mr Nicollier and a retired Nasa chief test pilot, Rogers Smith, will be among the multinational team guiding Mr Borschberg gently to altitudes of up to 8,500 metres over Switzerland and eastern France at speeds of about 70 kilometres per hour.