File Photo: Solar Impulse 2.
In a rare test of man and machine, The Solar Impulse 2, the world's only solar-powered aircraft is about to undertake its greatest challenge yet - to fly non-stop for six-days from China to Central Pacific.
The plane is powered completely by the sun and has been in Nanjing city in east China waiting for clearer skies during their journey to Hawaii in the Central Pacific.
The pilots have named this 8,000 kilometers fly, by far the longest leg of the trip as "The moment of truth."
Andre Borschberg, the aircraft's founder and pilot, will be alone in the cockpit during the non-stop flight.
"I am feeling a bit high, actually, in the sense that we have been working hard to find a window for many weeks," Mr Borschberg was quoted as saying by the BBC.
"I knew it would take time... but it wasn't easy to wait. It's going to be a discovery about how I feel and how I sustain myself during these 5-6 days in the air," he said.
So far on its epic round-the-world, Solar Impulse has only had to do short journeys of about 20 hours'.
For a passenger airliner, the 8,000 km journey would take around 10 hours. But for this solar-powered, prop-driven, experimental aircraft - it could take 5-6 days and nights of non-stop flight.
During their round-the-world journey, the plane had layovers at two cities, Ahmedabad and Varanasi.
The plane will cover some 35,000 kilometers, and the whole journey is expected to take at least five months to complete.