It will be a test of man and machine. The Solar Impulse project is waiting to undertake its greatest challenge yet: flying non-stop from Nanjing in China to Hawaii in the Central Pacific.
For a passenger airliner, the 8,000km could be completed in 10 hours or so. But for this solar-powered, prop-driven, experimental aircraft, it could take 5-6 days and nights of continuous flight.
The plane will need the weather on its side, which is why the team is currently sitting tight in Nanjing, looking out for a sizeable, favourable window.
So far on its epic round-the-world quest to promote clean technologies, Solar Impulse has been restricted to short hops of about 20 hours’ maximum duration.
To complete this seventh leg will involve smashing several aviation records - not least the longest-duration journey for a single-seater plane.
The Swiss entrepreneur and engineer Andre Borschberg, who will be at the controls, has supreme confidence in the technology, but he is in no doubt how tough the coming mission will be.
“It’s more in the end about myself; it’s going to be an inner voyage,” he told BBC News.
“It’s going to be a discovery about how I feel and how I sustain myself during these five or six days in the air.”
Borschberg will be strapped to his seat for the duration, confined in a cockpit no bigger than a phone booth.
He can take little catnaps of 20 minutes or so, and he will be practising yoga to try to keep his body fresh. He must be ready to react at very short notice.
Although it has a wingspan of over 70m, Solar Impulse only weighs a couple of tonnes, and dealing with any turbulence will require the attention of all his 40 years of flying experience.