Photograph by Philip Cheung, National Geographic
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André Borschberg, the CEO, co-founder, and co-pilot of Solar Impulse 2, poses in front of the craft before taking off in Abu Dhabi in February 2015.

Photograph by Philip Cheung, National Geographic

Exclusive: Pilot of Solar Plane Shares Secrets of 5-Day Flight

Swiss pilot battles exhaustion and weather during endurance mission.

Swiss pilot André Borschberg still has a long flight ahead. He took off Sunday afternoon from Nagoya, Japan, in the Solar Impulse 2, an experimental craft powered only by sunlight that is attempting to set a record as the first plane of its kind to circumnavigate the globe.

After several weather delays, Borschberg is finally en route to Hawaii, on the most difficult leg of the expedition, dubbed the “Earhart Leg” because it is roughly the same path on which Amelia Earhart disappeared 77 years ago. Borschberg is expected in Honolulu by Friday or Saturday.

We spoke with Borschberg via satellite uplink from his cramped cabin in the Solar Impulse 2:

How are you feeling now, after you have passed the point of no return in your flight?

Extremely fine. It was a very emotional start for many reasons. It was hard to get here! There were many technical questions and we didn’t know if we would proceed. We had a limited time window, it was hard to decide, and then we finally went, after waiting so many days and weeks.

This question comes from one of our readers: How do you deal with your nerves about the expedition when you are on the ground, waiting (sometimes for weeks) for the next leg?

If I get too emotionally involved, each time I don’t go I get so disappointed that it’s a deep blow in energy. So I try to stay detached and work on my tasks and the strategy.

How are you able to sleep while you're flying alone over this isolated stretch of ocean? Do you wake up and have a mini freakout?

It was very important on the first day to come down after all the excitement around the start of the mission. I used a lot of breathing techniques from yoga and meditation.

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A view inside the Solar Impulse 2 cockpit on June 30.

It has been difficult to sleep. We have sleeping periods of 20 minutes maximum, but to go into enough of a relaxed mode is difficult. Normally you are told not to sleep when you are a pilot and in a cockpit. Now it is the opposite, and it takes training and mental strength to believe that the aircraft will perform well when I sleep. Yoga and meditation helps.

This one is another reader question: Are you able to listen to music along the way?

Yes. Sometimes it’s classical music, which is relaxing. I also like music from the 1960s and 70s, which helps me remember the good old times. It depends on the situation. I’m also listening to Indian music, which is helpful to get into meditation.

Given all the weather-related delays that have affected the flight to date, do you think the craft has been more sensitive to weather than you expected?

The flight to Japan remains five to six days. Weather forecasting three to four days ahead is quite reliable but if you go further than that the reliability goes down dramatically. So we saw windows that looked too unreliable. It’s not that the aircraft couldn’t do it it’s that we didn’t want to gamble on risks from storms or heavy turbulence just to try it and see if it worked.

John Tomanio, NG STAFF
SOURCE: Solar Impulse

What have you learned from the technology from the project that will be useful for other applications?

The technology we use is extremely energy efficient; that’s the only way we can fly this airplane day and night. I am collecting energy during the day [through solar panels], and we have to have the highest efficiency to make it to the following day. Our motors have an efficiency of 97 percent. A typical car engine is barely 30 percent, meaning 70 percent of the fuel is burned for nothing. We see it works, and we can use them everywhere, which is the goal of our demonstration.

Normally pilots have to make navigation and other calculations based on the fuel they are burning, which changes the weight of their craft. But your fuel comes from the sun. Fuel seems more predictable than sunlight, so how does that change your role?

You still need to plan the route. For us everything is about energy and the aircraft is optimized to save energy.

How are you looking forward to the rest of this long flight?

It will only work if we really partner, the airplane and myself. I have to make sure it gets enough energy every day and it has to give me the possibility to recharge my own batteries. But what a privilege to be over the biggest ocean flying only with solar energy. We are fragile but so powerful with this possibility of unlimited endurance.

This interview has been edited and condensed.

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