DW: How did you choose the cities where you will be landing on your trip around the globe?

Borschberg: It's a mixture of different things: we have done a lot of simulations during the last seven years to determine which route to take, looking at weather patterns and so on. We definitely wanted to cross India and China early in the year - before monsoon season. Both countries are also extremely important for our message, which is to demonstrate the potential of clean technologies.

The same goes for the start of our journey, Abu Dhabi, which is famous for exporting oil, but at the same time they are beginning to invest heavily in the production of renewable energy. We also will have to cross two oceans, and we chose Nanjing on China's Pacific coast and New York on the Atlantic because we determined that these were optimal starting points for that.

DW: The Nanjing-Hawaii leg over the Pacific Ocean is going to be the most dangerous. Are you scared about being over water in an extremely light plane without fuel for five straight days?

Borschberg: You're right: This has never been done with such an airplane before, so we are really facing the unknown. It is really an exploration. We have to be prepared for the worst: for example, to jump out with a parachute and to let the airplane fall into the ocean. We did a lot of emergency training to be prepared for such scenarios, to be sure that we can handle the most difficult situations. And this has lessened our fears.

Piccard: It is the role of the pioneers and explorers to try to make history and to take risks. If you want to capture the imagination of the people, and if you want to promote new technologies, you have to do something that seems to be impossible. This means putting the bar almost unreachably high, and that's what we are doing.

DW: You will have to spend up to five days in a cockpit! How is this physically possible? Are you going to sleep?

Borschberg: The cabin is very tiny, but at least we have the chance to recline and change positions, which is important for a long flight. During the flight, we are going to do some physical exercise, yoga, for instance, and self-hypnosis to keep our bodies and minds fit. We also plan to take short naps - up to 20 minutes at a time - to get rest. We have been training ourselves with the help of a therapist for a while now. We have also adopted breathing techniques and meditation.

Piccard: This is an interesting fact about my relationship with André - we have different experiences, but we combine them to enrich each other. I never did yoga before I met him, but now I have started this form of exercise thanks to André.

DW: You also have different characters: did you have to fight over who would fly which leg?

Borschberg: Yes, we do tend to disagree. But we have always been able to find a solution that fits. Bertrand is the symbol of the project, and that's why we've agreed that he will finish the flight, bring the project to its end. I am more responsible for the technical aspects and the development of the plane, so I will start the trip and get the SI2 off the ground.

DW: You are obviously risking your lives - what for?

Piccard: If we put solar panels on normal airplanes, they would never be able to fly day and night. Our plane flies day and night because we have designed it to do so. This is a question of energy efficiency, and that is the message that we have for the energy policy makers of this world - use energy efficiently! If we could replace all technologies that pollute the world with new technologies that are cleaner, we would have already halved energy-consumption and reduced exhaust emissions.

DW: Solar Impulse 2 is your second solar-powered plane. Your team invested 12 years in its development. At this point, what kind of investment has been made?

Piccard: If you count everything - construction of the two planes, paying the team for 12 years, and putting together the flight missions - the budget will be around 150 million euros.

Interview conducted by Tatiana Ivanova