The Solar Impulse 2, the experimental plane attempting to fly around the world without a single drop of fuel, is set to take off from China early Tuesday morning on the most challenging and dangerous part of its journey yet.

The pilots and their team have even given the leg a name: "The moment of truth." Andre Borschberg, a Swiss engineer and former fighter pilot, will be alone in the cockpit during the non-stop flight from Nanjing to Hawaii.

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"I am feeling a bit high, actually, in the sense that we have been working hard to find a window for many weeks," Borschberg told CNN by phone from Nanjing on Monday.

"I knew it would take time... but it wasn't easy to wait."