It was 9am on July 8 when Andre Borschberg touched down in his Solar Impulse aircraft at the Payerne Air Base in Switzerland, after a record-breaking 26-hour flight powered solely by the sun.
The day before, as he flew above the picturesque Swiss countryside, his aircraft fuelled by the 12,000 solar cells built into its 70 metre wingspan, Mr Borschberg witnessed something unheard of among traditional pilots - the longer he flew, the higher his fuel gauge rose.
"It was extremely special to be able to climb to 9,000 metres but, at same time, see the fuel gauge going up, up, up, to 100 per cent," recalls the Swiss adventurer. "That for me was a totally new experience."
Mr Borschberg is one half of the Solar Impulse pilot team planning a solar-powered voyage around the world in 2013 or 2014. He and his flying partner, Dr Bertrand Piccard, wear several hats working on the project, which they hatched in 2003: adventurers; innovators; and ambassadors for clean technology.
They believe the world is in great need of a shot of pioneering spirit to inspire a new approach to the global energy predicament.
Dr Piccard came up with the idea of a fossil fuel-free circumnavigation of the globe in 1999, at the culmination of a world record set when he and Brian Jones, his British co-pilot, flew their balloon, the Orbiter 3, around the world on a 20-day, 45,000km journey.
"When you speak about dependency to fuel, in a normal world we don't care so much," Dr Piccard says. But during the balloon journey, the team saw its liquid propane fuel rapidly diminish from 3.7 tonnes at launch to just 40kg at the landing.
As the flight progressed, the pair recognised afresh the vulnerabilities in mankind's reliance on fossil fuels, he says. "You feel it in your gut. You know that if you are not landing before you are short of gas, you fall from the sky and crash."
Dr Piccard comes from a long line of adventurers: Auguste, his grandfather, was a balloonist who invented the pressurised cabin. In 1932, he and his co-pilot Max Cosyns used a pressurised chamber hung under their balloon to become the first people to ascend to a height of 16,200 metres.
Dr Piccard's father, Jacques, in 1960 became the first man along with his US co-pilot Don Walsh to reach the Marianas Trench, more than 10km below the surface of the Pacific Ocean, in a bathyscaphe.
The Orbiter journey was completed just before the millennium and the timing left Dr Piccard looking for new adventures. "I wondered, what is left to do with the pioneering spirit? What unbelievable goals can inspire us into the new millennium?"
The answer was Solar Impulse. With a team of 70, and with help from 80 corporate partners from sectors including finance, aerospace design, solar cells and composite materials, the project unveiled its first prototype aircraft in June last year.
Now, with possibly less than three years to go, the round-the-world project has raised US$80 million (Dh293.8m), with a further $35m needed. Dr Piccard hopes to involve Abu Dhabi, home to the Masdar City carbon-neutral project, by including UAE college students in the team.
The plan to circumnavigate the globe calls for the pilots to take turns completing legs of the journey, with each landing to hand over to the other. About five such stops are planned at points in Europe, Asia, the US mainland and Hawaii.
The aircraft is designed to use electricity from its solar cells to power its four propellers to climb to 9,000 metres and, at the same time, charge its batteries.
At night, the plane will descend slowly to 1,500 metres without using any power, then switch to battery energy stored during the previous daylight period to return to its cruising altitude.
With a wingspan greater than the 63 metres of a wide-body Airbus A340, the weight of a saloon car (1,600kg) and the power output of a scooter engine (40hp), the Solar Impulse is a most unusual aircraft.
The long wings create so much lift that the plane requires just 100 metres for take-off, which is achieved at 35kph. Cruising speed is 70kph. The light-weight, composite aircraft requires delicate handling: while a commercial aircraft may bank at 25 degrees, the Solar Impulse craft is designed to bank no more than five degrees - and then only in specific situations.
For his 26-hour flight in the summer, Mr Borschberg wore a special suit to cope with temperatures ranging from minus 18°C to 35°C.
The two pilots plan to make their journey around the world in a second version of the Solar Impulse that is currently being built. The new plane will have more cabin space for the pilot. The plane seats only one, and uncomfortably so.
Mass air transport using solar-powered aircraft is not Dr Piccard's goal. "Our goal is to carry messages," he says. Of course, commercial aviation may well incorporate solar technology in the future.
Aircraft have come a long way since December 17, 1903, when the Wright brothers made the first powered flight of a heavier-than-air craft, travelling just 800 metres, Mr Borschberg points out. "They said it would not be possible to fly over the Atlantic in an aeroplane, but Lindbergh did it 25 years later, and he was alone," he says.
"It took another 25 years to carry 100 people over that distance. The point we want to show is that [solar] technology works."
