Solar Impulse has already shown the potential for sun-based aviation in its attempt to fly around the world, but it just embarked on its most ambitious trip yet. Pilot Andre Borschberg has taken off from Nanjing, China on a cross-Pacific flight whose first leg ends in Kalaeloa, Hawaii -- 5,061 miles away. That's about 120 hours in the air, and should set records for both the longest single-seat flight ever as well as the first transpacific flight by a solar-powered aircraft. And did we mention that this leg is even more dangerous than previous parts of the journey? After a certain point, Borschberg's only choice in an emergency will be to bail over the Pacific and hope that his rescue goes smoothly.