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MS. DIANE REHMThanks for joining us. I'm Diane Rehm. This past weekend a plane called Solar Impulse landed in Washington D.C. after a multi-stop trip across the country. the solar powered plane is still decades away from becoming commercially viable but creators say few could've imagined what planes would become when the Wright brothers took to the air for the first time in 1903.

MS. DIANE REHMHere to talk about pioneering clean technology and their mission to fly a solar powered plane around the world, Bertrand Piccard and Andre Borschberg. They're the developers and pilots of "Solar Impulse." I hope you'll join us as we talk about this exciting voyage these two men are on. give us a call, 800-433-8850 send us your email to drshow@wamu.org, follow us on Facebook or send us a tweet. And good morning and welcome to both of you.

MR. ANDRE BORSCHBERGGood morning, Diane.

MR. BERTRAND PICCARDGood morning, Diane.

REHMGood to see you both. Bertrand Piccard, you are not only an aeronaut and explorer, you are also a psychiatrist. Would you please explain how you got into solar flight?

PICCARDIt's true that I love to explore the unknown and as a psychiatrist to explore the inner world and with a solar airplane you explore the outer world. and I think both are important to understand life.

REHMWhen did you actually begin this desire to develop a solar plane?

PICCARDWell, I think it starts very long ago. I come from a family of explorers and all the role models I had, my grandfather, my father, all the astronauts of the American Space Program I was fortunate enough to meet, have showed me that life is interesting if you explore it.

PICCARDAnd the unknown is a trigger, you know, my curiosity and I've always been interesting by scientific exploration, at the same time protection and understanding of the environment and nature. And Solar Impulse combines both and, but I think it became concrete when I did the flight around the world in the balloon and the balloon took off with the 3.7 tons of liquid propane and landed with 40 kilos after 20 days and 32,000 miles.

REHMWhoa.

PICCARDSo that was the trigger. I thought it was really tight, we almost ditched in the Atlantic before the success, so let's try to find a way to fly around the world but with no fuel at all in order to be completely independent from a fuel tank and potentially fly forever. And that was the beginning of the dream of "Solar Impulse."

REHMAnd Andre Borschberg, you're an engineer and a pilot used to dealing with the nuts and bolts, how did the two of you come together?

BORSCHBERGWell, interestingly, I'm a more entrepreneur than an engineer so I've been passionate about new projects, new ideas, innovation since ever and my education is engineering but I've never been involved in the construction of any airplanes.

BORSCHBERGSo in some ways it sounds strange, but it's also extremely interesting because I think both of us not having this experience were very open to new ideas, a new way of thinking, new technologies, maybe new solutions. So instead of being, I would say, a negative dimension it was very positive at the beginning of the project.

REHMAll right. And now I'd like you, Andre, to describe Solar Impulse for us.

BORSCHBERGSo Solar Impulse, it's an airplane which flies entirely and only with the solar energy. It collects its energy using solace, transform the sun rays into electricity. The electricity is used to run electric motors and propellers but also fuel batteries. That's the first airplane ever which can fly day and night many days, many nights almost perpetually using only the sun energy to propel the aircraft.

REHMBut, Bertrand, you have to land periodically, why?

PICCARDWell, the airplane could fly forever but the pilot is less sustainable than the airplane, you know. And on this first airplane even if we could have flown nonstop from San Francisco to New York or to Washington we have no autopilot, no toilets on board and every 20 to 24 hours we land to swap the pilots.

BORSCHBERGSo Andre made some of the flights, I made some of the flights and we also wanted to be in important places around the U.S. to show this airplane to schools, universities, high level politicians also to speak about our message of clean technologies.

REHMI was looking at the photographs and the film that we now have on our website, drshow.org, you can see this magnificent structure. The wingspan looks quite wide, tell me about that, Bertrand.

PICCARDYou know, yes when we started the project we understood that the quest for energy was paramount. In fact, we had two strategies which were possible. I mean, the first one was to embark as many technologies as possible to maximize the energy we would have on this airplane to be able to fly a very long time.

PICCARDThis was one way to look at it. The other way was just the other way around, was to minimize the energy consumptions of the airplane and reuse what we needed as energy to fly and that's what we did. And that's the reason why it's so big because when it's big the wingspan of a 747 it uses very little energy to fly horizontally. The power of a scooter, the size of a jumbo jet...

REHMThe power of a scooter?

PICCARDThe power of a scooter. That explains its huge dimension.

BORSCHBERGAs long as it is light enough because it's clear that if it had the weight of a 747 it would never fly on solar power.

REHMSo how much does it weigh?

BORSCHBERG3,500 pounds which means the weight of a small car. And like this it can have such a small sink rate that during the night the batteries are enough to keep the airplane airborne. If it was too heavy it would touch the ground before the next sunrise.

REHMBut it's huge on the outside, this wingspan, the size of it but inside what is there room for, two people? How do you manage that?

PICCARDNot yet for two people, for one person only exactly. That's the big thing.

REHMAnd the other one, and the other one has to sit where?

PICCARDThe other one sits on the ground so we exchange, that's also one reason why we do these stops. So one is on the ground and helps the pilot also to get to its destination while the other is flying.

REHMWhat's going to keep you awake while you're by yourself?

PICCARDPassion, passion, you know, we're both working on this project since more than 10 years. So when it's the moment to sit in the cockpit it's a privilege. It's a really extraordinary moment, you know, to fly an airplane that is completely unique.

PICCARDThere is not another airplane like that anywhere in the world and we know how many people sole support our message about clean technology so we carry on board a memory stick with the name of dozens of thousands of people who support us in our pioneering spirit. So with so many virtual passengers you're never alone and it's never, you know, there's no boredom. It's just amazing at every moment.

REHMHow much did building this plane cost?

BORSCHBERGIt's difficult to say exactly how much it cost to build it because at the same time a development and a design program and a construction program. So we had to rework on the new technologies, improve the technologies available and this with 80 different partners.

BORSCHBERGSo that's something we initiated 10 years ago and it took eight years, in fact, to build up the team, get the partners, do the design and the construction. It's more of a process than just a construction step.

REHMAny government help?

PICCARDNo, it's a program which is financed by mostly private institutions, private companies, private entities, private individuals. The Swiss government did help but with infrastructure. Not in financial terms but infrastructure was important, to be on airports, to have hangers. So that was, we needed to have this access.

REHMAndre Borschberg and Bertrand Piccard. Piccard is an aeronaut and explorer and a psychiatrist. He's chairman of Solar Impulse. Andre Borschberg is an engineer and pilot. He's cofounder and CEO of Solar Impulse. Do join us, 800-433-8850.

REHMThis trip, Bertrand, was in preparation for your next goal to fly around the world. Why is it so important to you to fly around the world in this plane?

PICCARDI believe that when you are a pioneer and innovator and explorer you always try to achieve the ultimate goal. You don't stop before the ultimate success. You know, a mountaineer wants to go to the top of the Everest, a diver wants to go to the bottom of the (unintelligible) .

PICCARDPilots of a solar airplane want to fly around the world and the step before around the world is across the U.S. so that's why we're here. You know, it's the country where aviation was born, it's mythical to fly coast to coast so that's where we are now. So far it's already very, very exciting but of course around the world is the ultimate we can achieve with an airplane that flies without fuel and that's why we want to do it.

REHMAnd after a short break we'll talk about whether and where you can see Solar Impulse. We'll take your calls, comments, stay with us.

REHMAnd welcome back. I'm talking with two men who are so excited about what they're doing. They have flown across the country in a totally solar-powered plane and it does gather energy. Even at night that plane can fly. Bertrand Piccard, Andre Borschberg, they're both here with me. And Solar Impulse, their gorgeous plane sits now out at Dulles Airport in the Dulles Air and Space Museum. And that public day, you said, is this Saturday. Is that correct?

BORSCHBERGIt is, yes. It's (unintelligible) ...

REHMWill it be all day long, people can go in to see it?

BORSCHBERGIt's not decided yet but people can discover when we will open up on our website, which is www.solarimpulse, one word, dot com.

REHMSolarimpulse, one word, dot com. And you will have a chance to see something really innovative. Bertrand, I must ask you about your collection of model airplanes.

PICCARDYou are very well informed.

REHMTell me about them.

PICCARDYou know, I'm always been fascinated by the history of aviation. And it's true that I collect all models of airplanes that you have on ashtrays, cigarette lighters, mirrors, book stands. There are a lot of things that have been the creation of artists in the last 100 years because they have also been inspired by aviation's history.

REHMSo you collect these model airplanes and you create them.

PICCARDWell, it's a little paradoxical because I'm fascinated by the clean technologies that allow a futuristic airplane like Solar Impulse to fly with no fuel. But on the other hand, I collect all models of airplanes because I think aviation's history has been so important for the world. So let's see aviation history continue in the future, but it's true that it starts way back in the past.

REHMAnd Andre, I gather you have a new found love of cowboy boots.

BORSCHBERGCowboy boots and cowboy hats, both really. I discovered that and I think it was my dream since a long time to own both of it and -- the both of them. And I made it real when I arrived in Texas.

REHMSomeone wants to know whether you bring the aircraft to Oshkosh Air Adventure in July this year, Bertrand.

PICCARDOshkosh is a fabulous air show and Andre and I have been there several times to give speeches about Solar Impulse. But it's unfortunately not in the good period of weather for Solar Impulse.

REHMI see.

PICCARDWe need very calm where there are no rain, no winds. And end of July north of Chicago is very windy. And we already had contacts with the organizers. And a lot of participants are asking us this question. So unfortunately the answer is no, for this time at least.

REHMAll right. Now, I understand Solar Impulse flies at only 40 miles an hour. Wouldn't you have to find a range much, much higher to make it around the world, Andre?

BORSCHBERGWhere we worked, first of all, on the duration of the flight. So that's an airplane which can fly perpetually day and night, many days, many weeks, as long of course that it gets the sun in the morning when the batteries are almost empty. So speed was not what was I would say the key that I mentioned. But of course when you don't have to go down to refuel, you save a lot of time as well.

BORSCHBERGIf you talk about the flight around the world, we expect the flight itself to last about 20 days, 20 nights from one continent to the next. And the longest leg where it can last up to five days, five nights alone in the cockpit because the second airplane will have only seat. So that's what we are working on. We have a sustainable airplane and we really have to work on making the pilot sustainable as well.

REHMWhy is there only room for one pilot? Wouldn't you desire to have a co-pilot?

BORSCHBERGYes, we would. I mean, we have -- in some ways, we have it, but not on the airplane. We have a team on the ground, which is supervising, helping, planning, steering, preparing the flights. And that's very big help, but that's true, it's on the ground. But it's not just adding a pilot. It's adding a pilot, that needs oxygen, needs food, the space, the seat, maybe a parachute. So that's 500 pounds more. And the 500 pounds more are not feasible with today's technology.

BORSCHBERGIt may be possible in a few years, but we are still -- at the time, you know, if you compare to traditional aviation, we are 1915, 1920, we're pioneers. We're starting to cross the country, still unable to cross the ocean. So it'll be at the same stage with this kind of aviation.

REHMAnd at what speed would you believe you will go as you go around the world?

PICCARDWe're flying roughly 40 miles an hour.

REHMAnd that's what you're doing now.

PICCARDYes. And if...

REHMYou don't expect that speed to increase.

PICCARDYou know, if you would double the speed, you would need to collect eight times more energy...

REHMI see.

PICCARD...which is not possible for us at this stage. And if you add the second pilot and the weight of his equipment, you would need to subtract this from the batteries. So you would have less batteries, which is also not possible. So everything is pushed to the limit. We do the best we can with the technologies we've developed with our partners. But more that what we do now is not possible today. It will probably be possible in the future.

PICCARDBut, you know, when the Wright Brothers were flying, they were alone onboard. They were flying 40 miles an hour. They had the same power then we have. And they flew 200 meters. And 66 years later there were two men on the moon. So we're starting now a new cycle. We have a little bit of constraints and limitations because we're doing it with no fuel at all, so it's completely new. And maybe it will lead us very far in the future for other applications.

REHMIs it true that you actually met Charles Lindbergh as a child?

PICCARDYes, it's true. I was 11 years old. I was invited by Venifin Brown (sp?) to see 6 Apollo taking off. And the last Apollo mission I saw starting was Apollo 12 and Charles Lindbergh was there for the reception given by NASA. And then we spent a moment together and it was a fascinating moment.

REHMDid you, at that time, have dreams of your own?

PICCARDYou know, I had dreams when I was a child about aviation, about the conquest of space. I was building small plastic models of airplanes. And I thought it would always remain a dream. And then I moved to the U.S. with my family for two years and that was the time of the Apollo space program. And I met most of the American astronauts. And I met Charles Lindbergh. And I saw that all the dreams I had were absolute reality.

PICCARDAnd the people I was reading about in books and newspapers were, I would say, real and normal human beings, I mean, human beings who were talking with me as a child, who were explaining to me what they were doing. And suddenly I had this very, very strong experience that the dreams can become a reality if we have commitment, if we have perseverance and if we believe in the power of our dreams. And that was a life-changing experience for me when I was 11 years old.

REHMAnd Andre, did you have the same kind of passion?

BORSCHBERGYeah, and part of this generation who could watch the first man on the moon. And I think it was fascinating, inspiring, so yes, the dream was there. I realized part of my dream by joining the Air Force and could fly in the squadron's jet fighters for 25 years next to my professional activities so I could do both, being an entrepreneur and fly these fabulous airplanes.

BORSCHBERGI moved slowly more to the business part of my professional activities. And this project brought me back -- and the idea of Bertrand really brought me back to my dreams and maybe my fascination about exploration.

REHMYet it's fascinating to me, Bertrand, that you became a psychiatrist and an expert in hypnosis. How does that affect you either in flight or in your daily life?

PICCARDHypnosis is something that allows you as a human being to use better your inner resources, your concentration, your focus, your emotions, the feeling of yourself living in the present moment in your body, all these things we call now mindfulness. And hypnosis is a therapeutical way to use it but it's also a personal way to understand life and understand the relation with ourselves. I do a lot of self hypnosis also.

PICCARDSo not only I treated my patients like this but I also use a lot of these techniques for my normal life and of course to prepare my flights and to fly. In the balloon I was sleeping with self hypnosis and I was falling asleep much quicker because I could disconnect my brain from overstress of the piloting of the balloon when we were in tricky situations around the world, to be able to sleep and relax.

REHMSo the relaxation part of it you think really helps you to do what you do when you are flying?

PICCARDThe relaxation is a part of it but the way you use the focus of your mind also. In very short words, hypnosis is a disassociation between two parts of yourself, mind and the body or the rational part and the emotional part of yourself or the past and the present or the past and the future. So you can, for example, anticipate a feeling of comfort and safety in the future while visualizing a big problem you have to solve.

PICCARDSo when you get yourself into potential problem in the future, you are calm and relaxed to solve it and to implement the solution you have prepared already. So it's a very good way, I believe, to live as a pilot but also in life in general. You know, human beings have so much in their resources that what they believe. And the big adventure is life itself. It's how to manage yourself as human beings.

REHMAnd I do want to remind you, you can see videos and photos of Solar Impulse at our website drshow.org. You can see those right now. You can see Solar Impulse, the plane itself at the Smithsonian Air and Space at Dulles this Saturday from 10:00 am to 5:00 pm. And you're listening to "The Diane Rehm Show." Going to open the phones now, 800-433-8850. First to Ramon in Grand Rapids, Mich. Good morning, you're on the air.

RAMONHi, Diane.

REHMHi.

RAMONI have a question that your guests have touched on already. And I'm wondering about the commercialization of solar-powered flight and the obstacles that lie between where we are now and where we might be in the future. Your guests said that there were two paths and they took the path of lessening the amount of energy needed for the flight. And I'm wondering if they are collaborating with any groups that are working on the other direction of making the batteries were efficient while being lighter, the solar cells to create more power from the sunlight, and material finance to make the aircraft lighter so it can carry more commercialized people or product.

REHMAndre.

BORSCHBERGIf we look at the future that's interesting also to do the comparison with the past. And recently, I mean, when we were in Cincinnati, close to Dayton, the hometown of the Wright Brothers, we had the chance to meet the grand-grand nephew of Orville Wright. And he told me that he -- I mean, that he heard his two grand-grand uncles saying that every time they leave the first flight, they could not imagine where passengers really flying long distance in an airplane. So I think it's very difficult to anticipate where we are going.

BORSCHBERGBut as to your question from the technology point of view, I mean, that's true, to make it possible to fly day and night we didn't just make one breakthrough. We had to work on all the different technologies that we need in this airplane. So that's improving the efficiency of the motors. I think we reached an efficiency now which is getting close to 100 percent of it. The motors, including the gear box is 94 percent, so we have only 6 percent losses.

BORSCHBERGIf you compare this with a turbine engine and some -- I mean, engines you have in your car, the efficiency's only 30 percent. So it's a tremendous difference. We worked on batteries to make them lighter. We worked on the solar cells with the supplies to make this more efficient, and all the materials also to achieve weight saving. So the successions of a lot of research which has been done and all these technologies are not just for the airplane. They have been brought to us by companies which have customers in different fields, in home buildings, in automotive, in appliances.

BORSCHBERGAnd their motivation is to achieve the same, which is to reduce the energy consumption of their clients by bringing products which really fits this need and this objective.

REHMBertrand.

PICCARDAnother way to answer to this question is to say that our goal is not to make a revolution in air transport. Our goal is to make a revolution in the mindset of the people when they think in terms of energy, in terms of clean technologies and energy savings. Because in the past when we spoke about saving energy, it was really a threat for mobility, for lifestyle and so on. And now when we speak of energy saving we speak about clean technologies that allow to protect the environment of course, but also allows to create jobs, to make profit, to assist in the growth of the industry.

PICCARDAnd it's a big win-win that will let people to understand so the people can use also in their daily life the type of technology we have on our airplane.

REHMRamon, does that answer it for you?

RAMONOh, it does. It makes me very hopeful to have these two gentlemen working on this process.

REHMIndeed. Thank you so much for your call.

RAMONThank you.

REHMYou know, when I asked you earlier about coming together, I never really got an explanation as to how the two of you came to work together. Andre.

BORSCHBERGBertrand had this vision to fly around the world with renewable energies already when he flew around the world with a balloon. I took off with full tanks of propane, landed with only 40 kilograms, just after the crossing of the Atlantic so not knowing if he would reach the course. So it was really a big suspense in the gondola. So at the time he started to think, would it be possible to fly without the dependence of oil?

REHMAnd we'll stop right there. When we come back, more of your calls, your questions. Stay with us.

REHMAnd welcome back to men who have just flown across the country in a solar powered plane are with me. Bertrand Piccard and Andre Borschberg, they're the chairmen, co-founder, CEO of Solar Impulse. That's the name of the plane. Now in the Dulles Air and Space Museum you'll be able to see that plane from 10:00 to 5:00 this coming Saturday. Right now you can go to our website, drshow.org. You can see videos and photos of Solar Impulse. Here's an email from Marilyn who says, "Increased air turbulence caused by global warming is already having an impact on the routes of big commercial jets. What is your route and your altitude? And how do you anticipate dealing with that turbulence?" Andre.

BORSCHBERGYeah, that's true that we see changes in the weather patterns all over. Our route will be, for example, in Southeast Asia, south of the Himalayas. And it's known effect to where the monsoon starting in May. Fifteen years ago the monsoon will start May 20 plus, minus one day. Now it's erratic, so it makes our life and the prediction of the weather more difficult. And, of course, to bring this airplane in unpredictable methodology is also a very, very big challenge for our team on the ground.

REHMHow many people are on the ground as you move across the United States? I mean, you say you're communicating with them, they're watching out for you. How many are there?

PICCARDWe have 45 people with us in the U.S. and 15 people in Switzerland in our mission control center, weathermen, air traffic controllers, technicians, electricians, engineers, IT people, flight director. And it's only fair to say the commitment of everybody on our team. You know, we don't have the impression to work. We just have the impression to have a part of our life together and achieving the result of our passion.

REHMHere's an tweet that says, "Solar flight is not completely new. What new or more recent technology is in Solar Impulse?" Bertrand.

PICCARDWell, up to know there were solar powered planes, since 30 years. But they could only fly in the middle of the day with full sunshine. And although it was pioneering feat and we admired very much, in fact, it was much more showing the limits of solar power than the potential. Solar Impulse with these new technologies, clean techs with the batteries onboard show the potential of solar power, because we can store the energy when we fly during the day to fly during the night also, reach the next sunrise, continue the next day. And in that sense show that with solar power we can potentially stay in the air perpetually.

REHMInteresting. To Tulsa, Okla. Good morning, Brian.

BRIANGood morning, Diane.

REHMHi.

BRIANGoogle recently was experimenting with helium balloons to provide internet service to hard to reach global areas, but obviously they were having issues with the duration of the balloons themselves. Could they use a version of this plane and its possible perpetual service for that applied technology?

BORSCHBERGCertainly, yes. I think a short term potential follow-up on what we are doing would be the build-up of high altitude flying platforms. It's easy, in fact, to have today an unmanned airplane flying with technology onboard that to bring a man in such an airplane. So we could certainly save a lot of weight and have an airplane flying at 20 kilometers altitude and staying for six months.

REHMInteresting. Here's an email from Julie in Cincinnati, Ohio who had the pleasure of seeing Solar Impulse make the unexpected stop in Cincinnati over the weekend. I gather your plane was delayed taking off due to the amount of moisture either from dew or fog that had accumulated on the wings overnight. Please explain what the concern was with the moisture and the care it took to remove it from the wings. Also, can the plane fly through the rain? Bertrand.

PICCARDI have to say it was my most stressful moment in this adventure across America. I was in the cockpit of the airplane. The heat was coming. The thermal turbulences were coming. There were clouds coming from the west. And at the same time the airplane was full of water and we had the team who had to...

REHMDo you mean in the cockpit as well?

PICCARDNot in the cockpit...

REHMNot inside.

PICCARD...because it was protected.

REHMOkay.

PICCARDBut inside the wing and inside the ailerons. And the fog had condensed on the wings. And when we tried to remove the water from the wing, it fell into the ailerons. And the ailerons are very, very thin pieces of carbon fiber. It's extremely light. So it has to be well-balanced. If suddenly it's full of water, it becomes much heavier. And when you start to activate the ailerons, it can do what we call a flutter. It means the ailerons start to vibrate very strongly and can be torn apart from the wing.

PICCARDSo, of course, there was no way to take off with ailerons full of water. But there was also no way to be stuck in Cincinnati, there for another week because the Minister of Energy, the Secretary of Energy of the United States was waiting for us in Washington. So it was a really, I tell you, stressful moment in that cockpit.

REHMOh, my goodness.

PICCARDI was boiling.

REHMAndre.

BORSCHBERGYeah, you have to realize that this first -- this first airplane is a prototype airplane. It was really designed, built to demonstrate we can fly day and night.

REHMYes.

BORSCHBERGBut it flew so well that we started to accept the invitation of Brussels, of Paris, of Morocco and now decided to bring this airplane to the United States because of its flight characteristics. But it was not designed for that. The second airplane will be designed to travel. And with the second airplane, we'll be able to fly through clouds. And we'll be able to get this humidity and not having the problem we had here.

REHMSo to answer the second part of that question, it cannot fly through the rain.

PICCARDThis first airplane cannot. The second will be able to.

REHMAll right. And here's another tweet. "This is also the era of the drone. Do you foresee solar powered drones?"

BORSCHBERGWell, we can foresee solar powered drones. But if you have no pilot to come for the interview in your show because you only have a robot, it's not so fun.

REHMBut you can foresee that happening? Oh, my goodness. All right. Let's take a call here in Washington, D.C. Good morning, Steve.

STEVEGood morning, Diane. And good morning to the great aviators. And by the way, it's wonderful to hear your accent. I hearken back to Jacques Cousteau who all Americans miss very much.

REHMIndeed.

STEVESo anyway, I'm a private pilot and had a couple of functional questions. First off, most of the listeners don't realize that you can either be a victim or a benefactor of winds of law. And at an airspeed of 40 miles an hour, if you have a 35 mile an hour headwind, you're almost at a standstill. Or if you have a 35 mile an hour tailwind, of course, you can accelerate tremendously. How much of an effect is that on your flight planning?

BORSCHBERGWell, that's extremely important and that's the reasons why normally we take off early in the morning and land late at night when the wind is calmer. But we had one experience which is exactly, you know, very close to what you said. When I arrived over Dulles Airport, the wind intensity or the wind speed was the same intensity as the maximum approach speed of the airplane, which means the only way, in fact, to land was to keep the nose of the airplane towards the wind. If I would make a turn, the airplane would've been blown away.

BORSCHBERGSo instead of making a traffic pattern like you usually do with an airplane, I just did a translation, a little bit like in a helicopter, and bring it down through the translation on the runway's threshold and landing this airplane almost stationary. So that was also a discovery and almost exploration in flying.

STEVEYeah, that's fascinating. Also, you know, I'm excited every time I go aloft in a little piper, certainly different than what you're piloting. But nevertheless, those long flight times can get exhausting even with the most exuberant pilot. Do you have autopilot? Or how do you mitigate that? And I warn you the FAA is listening.

PICCARDYes. And, you know, we have very, very good relations with the FAA. I would even say it's thanks to them that we can do this flight. Because they accepted this slow airplane into heavy traffic. And the air traffic controllers in America, I tell you, are really efficient.

REHMHow did they manage your path?

PICCARDWell, we have a transponder on the airplane so they can follow us on the radar. For landing and taking off, we do it before and after the closing of the airport. But in the air, very often, we have a 747 underneath, we have a 767 on top, we have an Airbus on the side. And it's perfectly well-managed because of these new technologies of air traffic control.

REHMWow.

BORSCHBERGAnd the FAA worked two months, in fact, really on each leg to help us make it feasible, so...

REHMAnd what about the second part of this question, the stress on the individual pilot?

PICCARDWhen I drive my car or when I fly with a normal airplane, it's true that every hour and a half, every two hours I feel tired. And it's normal, you know, it cycles...

REHMSure.

PICCARD...we have during the day and the night. But when I fly a unique airplane that exists nowhere else, it's such a privilege that I would feel ashamed to be tired and to sleep in the airplane, you know. And honestly I feel much better, much more concentrated, much more focused when I am in these moments of flying. And this is maybe a learning for everybody. When we are in the routine, when we are in the normal way of life, you know, when we just have the spirit going everywhere and we don't really focus on what we're doing, life is not exciting enough to keep us really aware of what's happening.

PICCARDBut when we are in extraordinary moment, that in moment out of what we're used to do, out of every habit, out of every paradigm and common assumption, that's a real adventure. That's the moment where the mind stays alert, where we are focused, when we are aware of what's happening. And I would even say that flying this airplane for 20 hours is a philosophical experience, because we are so much aware of what we're doing, alert, all the mindfulness we have in this moment, and sometimes it's a little sad to land and come back to the normal world.

REHMBut, Andre, you were a jet pilot in the Swiss Air Force. This has got to be so different for you from flying jets.

BORSCHBERGIn some ways, yes, in other way, no. I think flying, if you're passionate, being in this third dimension, it's a feeling of -- well, it's a feeling of liberty first. It's also getting -- having a different view on the earth under you and the beauty of it. So I think you take distance with a ground, but you may also take distance with yourself and what you do. So this is I would say the same, you know, if you fly fast, if you fly slow. The big advantage with this airplane is that we have time. And so we have time to let it go. We have time to be. We have time to enjoy. And I think this is a fantastic experience.

REHMAnd you're listening to "The Diane Rehm Show." To Jacksonville, Fla. Good morning, Gordon.

GORDONGood morning, Diane. I'm a big fan of the show. First time caller.

REHMThank you.

GORDONThis is such an interesting topic. And you've answered one of the questions, and that was airspeed, which is 40 miles per hour. So I'm guessing that the vast wingspan of this aircraft is to sustain lift at such a low speed. And my other question was, at what altitude do you fly the plane?

BORSCHBERGYou're absolutely right. In fact, the size of the airplane is to provide the best lift and also allow us to use as little energy as possible to fly the airplane. So you have more lift and less drag. More benefit and less losses. Regarding the altitude, altitude is a source of energy for the night flight, so we climb to 27 in the United States, 27,000 feet, which is the altitude...

REHMReally?

BORSCHBERG...of the airliners, yes.

REHMWow.

BORSCHBERGYeah, so that's to be above the clouds, but that's also maybe to be closer to the sun and therefore being able to collect more energy. But that's the way, in fact, to store energy and altitude that we release at the beginning of the night descending to, let's say, 10,000 feet and then using the energy from the batteries. By using both altitude and batteries, we can fly up to 12 hours and therefore through the night.

REHMI hope that answers it, Gordon.

GORDONAbsolutely, Diane. That's an absolutely amazing endeavor and the best of luck in the future with your flights.

BORSCHBERGThank you. Thank you.

PICCARDThank you very much. And say hello to Florida from me. It's where I lived two years as a child to see the takeoff...

REHMOh, how wonderful.

PICCARD...of Apollo. It's a great place to live. I enjoyed it so much.

REHMI was there for one of those takeoffs as well. One last question for you both from Michael. How difficult was it for you to cross the Rocky Mountains?

PICCARDWell, it was actually difficult to find the good weather slots for the Rocky Mountains, so we decided to go around. And from San Francisco we went down to Phoenix before going to Dulles, instead of crossing to Denver as we felt in the beginning and to follow on the higher altitude.

REHMHere's another question. Does Solar Impulse takeoff on its own power or is it power-assisted?

BORSCHBERGNo, it's fully independent. That was very important when we defined the kind of airplane we wanted to build. To have an airplane which is fully autonomous from takeoff to landing. So it takes off over 400 to 500 feet, so pretty quickly.

REHMThese are quick questions for you. Do you use the same lithium ion battery technology developed by Tesla Motors?

BORSCHBERGIt's very similar, it's not the same.

REHMNot the same.

BORSCHBERGIt's a current technology, but I think we have -- interestingly, we have the same energy capacity as the best Tesla S car.

REHMAnd...

BORSCHBERGWhich is a fantastic car, I have to say. I don't want to make advertisement, but I really believe it.

REHMThat's okay. That's okay. And, finally, at sunrise, at what elevation angle do the solar cells begin to develop energy?

PICCARDAbout 15 degrees.

REHMFifteen degrees.

PICCARDYeah, which means roughly one and a half hour to two hour after the first rays of the sun at sunrise.

REHMWell, if you want to see this glorious plane, be at Dulles Airport this Saturday between 10:00 and 5:00 at the Smithsonian Air and Space at Dulles. And you can see photographs, films of Solar Impulse at our website now, drshow.org. Bertrand Piccard, Andre Borschberg, congratulations to both of you.

PICCARDThank you for the invitation. We love to share our experience with others...

REHMThank you.

PICCARD...especially with you.

REHMAnd we loved it.

BORSCHBERGThank you very much. Great pleasure.

REHMThank you all for listening. I'm Diane Rehm.