Solar Impulse plane prepares for longest leg of round-the-world journey

The longest, most anxiety-inducing leg of Solar Impulse’s round-the-world journey is set to begin on Thursday this week – weather permitting – as Swiss co-pilot Andre Borschberg, 62, assumes control of the aircraft for five days and five nights as it crosses the Pacific from China to Hawaii.

Having begun its solar-powered circumnavigation of the globe in Abu Dhabi in March, the mission is on schedule to arrive back in the Middle East later in the summer, but must now tackle the most arduous leg of the journey.

Flying 8,175 kilometers from Nanjing in eastern China to Hawaii in the Pacific Ocean, the journey is the seventh of 12 scheduled legs. So far, all journeys have been less than 20 hours in duration, but the 120 hours it will take to reach Hawaii are set to test both the plane’s and the pilot’s limits.

"It is the most challenging leg, yes, in the sense that we never before flew over the oceans," Borschberg told Yahoo! News. "There are of course also question marks with the type of airplane we have. Is it capable to fly solo with this type of energy, and of course the challenge is on the pilot side as well – can I stay alert for this leg and be able to pilot this airplane? Can I keep my energy at the right level? Can I keep my spirits, my mindset right to get this airplane to Hawaii?"

Borschberg and fellow pilot Bertrand Piccard have spent years learning meditation techniques that will enable them to sleep in 20-minute spurts, and have developed a specialized diet to ensure their bodies are in peak condition. However, despite the presence of a dedicated ground crew analyzing the plane’s trajectory at all times, this five-day leg will be the most punishing challenge yet for the experienced Borschberg.

Climbing to an altitude of 29,500 feet, the solar-powered Solar Impulse 2 (which is fitted with more than 17,000 SunPower solar cells) will be buffeted by high winds and subjected to temperature swings of 35C to minus 20C, all in the space just a few hours. "It is winter and summer every day in the cockpit," Borschberg noted.

Once the plane has touched down in Hawaii, the next few stops are scheduled for the U.S. mainland – first Phoenix, and then on to New York before the second ocean crossing, taking the plane to either southern Europe or north Africa, depending on weather conditions at that time.