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.
There's still a long way to go after this. The next phase will see Solar Impulse travel "just" 2,917 miles to Phoenix, Arizona, and there are still four legs after that -- the last two of which may take nearly as long as the China-to-Hawaii run. It'll be worth the effort if Borschberg and fellow pilot Bertrand Piccard can raise awareness about renewable energy, but this eco-friendly globetrotting definitely isn't for the faint-hearted.
Update (6/1/15): Due to inclement weather, the flight was cut short. Solar Impulse is set to land at Nagoya Airfield in Japan. You can watch live here.
[Image credit: Johannes Eisele/AFP/Getty Images]