NOVA

NARRATOR

A mission like no other. A plane powered only by the sun. (cheers) Set to fly around the world without a drop of fuel. What we do in the air, we can do on the ground. And this is our message. This journey will push the limits of technology.

NILS RYSER

It's made of fabric, it's made of carbon, and you can break it with your finger. (rain falling)

NARRATOR

It will test the endurance of its pilots.

MICHAEL ANGER

Do something wrong, just one thing, they could die, and you carry that for your, for the rest of your life.

NARRATOR

Flying solo day and night.

ANDRE BORSCHBERG

We never flew over the ocean. Five nights in a row, that's the main challenge. (switch clicks, beeping)

PICCARD

Switching on the solar generators.

NARRATOR

They will risk their lives.

WIM DE TROYER

There's bad weather coming in and then thunderstorms, and afterwards it's turning northwest.

RAYMOND CLERC

Either we divert, or we take a big risk.

NARRATOR

To realize a dream for our planet.

PICCARD

The decision we take goes far beyond the flight itself.

NARRATOR

"The Impossible Flight," right now on "NOVA." To fly, fueled only by the power of the sun. It's an audacious idea that gave rise to an airplane unlike any other ever built, now embarking on a revolutionary and risky mission. (distant alarm sounding) (alarm sounding) The risk is really high. I don't want to gamble with a pilot in the ocean.

PICCARD

A lot of people can be a little bit afraid, scared, by the unknown in which we are jumping.

NARRATOR

A perilous journey, 26,000 miles around the world, without a drop of fuel.

PETER FREI (on radio)

I think it's very dangerous. You know, we never have the story of those who got killed.

BORSCHBERG

We have to do it to demonstrate it works. So someone has to do it first. Someone has to try. (jet engines roaring)

NARRATOR

The zero-fuel flight begins in Abu Dhabi in the United Arab Emirates, where the sun's energy is in abundance nearly every day of the year.

PICCARD

To have an airplane that could fly forever without fuel. No noise, no pollution. That was the dream from the beginning.

MAN

We can move up a little bit. Just a little bit, just a little bit-- a little.

NARRATOR

It was a dream that aviation experts quickly dismissed. A solar plane capable of carrying a person around the world would have to be too big, too light, and likely impossible to control.

PICCARD

There are moments where you have to take some risks if you want to achieve something that has never been done. Otherwise, we stay in the armchair, and we wait until we're old and we do nothing. (speaking foreign language)

REPORTER

We're in the early hours of the morning here. The Solar Impulse 2 is ready to embark on its ambitious round-the-world journey. (engines spinning up)

NARRATOR

After weeks of flight tests over Abu Dhabi, the airplane, known as Solar Impulse, prepares for takeoff. Over 3,000 miles away, flight operations are run from a command center in Monaco.

ANGER (on radio)

Okay, Andr, everything is ready. We still wait for the final go from the SRB. (radio chatter)

NARRATOR

The project is the brainchild of Bertrand Piccard, psychiatrist, adventurer, and heir to a family legacy of scientific exploration.

PICCARD

In 1969, I was 11, and I saw Apollo 11 taking off to the moon. And I said, "I want to have that type of life." 16 years I've been dreaming of that, the art of flight around the world with no fuel. There are doubts all the time, but... When you're doing something that nobody has done before, the doubts are important. If you are on a straight line with your beliefs, you never succeed in something new.

CHRISTOPH ETTER

Solar Impulse from Solar Ground, confirm you get the clearance. Okay, solar generator looks good. Continue with engines, then. Have a good flight, Andr. Let's start the adventure. (beep)

BORSCHBERG (on radio)

Okay, finally. It's the magic, magic moment. (engines running) Main wheel liftoff. (cheers)

PICCARD

(weeping) Thank you very much. Currently altitude 5,300 feet.

NARRATOR

To help make his dream a reality, Bertrand turned to Andr Borschberg-- a man known for pushing boundaries, both as a fighter pilot in the Swiss Air Force and an engineer with a graduate degree from M.I.T.

BORSCHBERG

The airplane was considered to be possible to be built and flown. The challenge is how? I mean, to make something like this, huh? Here is an airplane we designed, we dreamt about. It's a big part of, part of me.

REPORTER

It's really a phenomenal sight, but crazy to believe that it is just the sun powering that plane here... Their dream is to show a way forward without fossil fuels and spread a message about the need to fight climate change.

NARRATOR

They are planning on about 12 flight legs. With only one seat in the plane, the pilots will have to take turns in the cockpit. The most difficult will be the flights over the world's two largest oceans, lasting anywhere from three to five days. At an average speed of just 45 miles an hour, the 26,000-mile trip will be long and full of uncertainty.

PICCARD

Five months now, the plane, starting this way, if everything goes well, comes back this way in July. It is so much more difficult to use these clean technologies in the air than to use them on the ground. So if it works in the air, I really hope people will understand that they can replace all these old, polluting old stuff by new, clean technologies. What we do in the air we can do on the ground, and this is our message.

BORSCHBERG

When you fly with the sun as the only source of energy, that's a completely different world, a different feeling.

NARRATOR

The revolutionary plane is powered by over 17,000 solar cells that collect and transform the sun's rays into electricity. That energy is distributed to four 17-horsepower engines, each with the daily power output of a small motor scooter. Any spare energy is stored in four lithium-polymer batteries, which enable the plane to fly at night or under cloud cover. The dilemma was how to build something big enough to collect maximum sunlight, but light enough to run on as little energy as possible. The trade-off was instability in anything but perfect weather. The plane is fragile and vulnerable to the elements.

LUC TRULLEMANS (on radio)

Hello, Andr. Below you, you have a small thermal inversion, and below this thermal inversion, you have all this dust and haze.

NARRATOR

At mission control in Monaco, a team of meteorologists, engineers, and mission planners-- many of them also highly trained pilots-- monitors an array of instrumentation and weather models during flight.

ENGINEER

You can put some more power...

NARRATOR

Lead meteorologist Luc Trullemans has guided long-range aviation and ballooning expeditions across the globe. But this mission presents a unique challenge.

TRULLEMANS

This aircraft is so light, so fragile, trying to find the places where he can fly is not so easy. When you have a downdraft or updrafts, this aircraft can break in two. Rain, humidity, and turbulence, forget it. Only sun and quiet weather and tailwinds.

NARRATOR

On this flight, they must steer clear of dust storms and turbulence caused by heat rising off the desert. Each flight leg will have its own difficulties, like avoiding thunderstorms and crosswinds, which could blow the plane off course. (radio chatter)

ANGER

We are excited, but there's a lot of fear, as well. I think the overall round-the-world flight you can compare to an Apollo mission. If you do something wrong, just one thing, they could die, and you carry that for your, for the rest of your life.

MAN (on radio)

Two meters. One meter. (wheel hits ground)

NARRATOR

The most dangerous part of every flight is the landing, where the fragile wings are that much closer to the ground. This pit stop in Muscat, Oman, is just long enough to clean the dust off the solar wings before the next leg to Ahmedabad, India. The team back in Monaco plans on using high-altitude winds to push the plane away from incoming clouds. These thin and wispy cirrus clouds could block a critical amount of sunlight. For this 15-hour flight across the Arabian Sea, Bertrand will take the controls.

PICCARD

Microphone and headphone, and the cuffs-- when it starts to vibrate on your arm, and this is to alert the pilot if the bank is too, too high.

NARRATOR

With no heat in the cockpit, the pilots must wear heated boots and a sub-zero-rated parka. Inside the cockpit, temperatures will range from minus 4 degrees Fahrenheit to 95 degrees when they descend during the summer heat. Solar Impulse's ground crew readies the plane to take off before sunrise to avoid turbulence and stay one step ahead of the clouds. (speaking foreign language)

PICCARD

When I was a child, I was afraid to climb in the tree. Fear is there. Either you have no fear at all, which means you're completely crazy, or you have some fear, which means that you are not a daredevil. It might not go well, but the only way to know is to try. Solar Impulse-- Solar Control.

NARRATOR

Bertrand's passion for exploration has deep family roots.

PICCARD

What interests me the most is not to break a record, but to do a first. My father and my grandfather were the first to the bottom of the ocean, showing there was life in the deepest trenches. The first in the stratosphere, to see with his own eyes the curvature of the Earth. (crowd cheering) When you do the first, you establish the first benchmark. And from there, a lot of new things can come out. I flew 20 days nonstop with a balloon. Every day I was afraid to fall short of fuel. And it was almost a failure. We just succeeded because we had two hours of margin with the propane after 20 days. And that's when I made the promise that I would fly around the world with no fuel.

NARRATOR

Flying balloons is one thing. Flying an experimental solar-powered plane is quite another. Bertrand only got his pilot's license in his 50s and he couldn't have picked a more difficult airplane to learn how to fly. Because it is so big and light, it's particularly unwieldy. Banking more than ten degrees will throw the plane into a tailspin. And because it's underpowered, there's no quick way out of danger. After 12 hours in flight, as he approaches the airport in Ahmedabad, Bertrand runs into trouble. (beeping) (radio chatter)

PICCARD

I have oscillations like hell. It's crazy. I never saw Solar Impulse do so unstable. You said the aircraft is unstable, and I don't see any turbulence at all. It's unstable on the heading. Did you see what happened just now? Yeah, I see it. It's a heading change of 15 degrees,

without any problem from outside. PICCARD

Yeah, yeah. From what I see on the data, it looks just perfectly calm.

NARRATOR

Alarmed, and puzzled by what's causing the problem, mission control in Monaco sets up an emergency call with Andr, who is already at the Ahmedabad airport.

CHRISTOPH SCHLETTIG (on phone)

There he is-- Andr, hello. Bertrand started to say the aircraft is unstable, and the autopilot cannot be connected and had a few times sideslips of up to 15 degrees, and he said it's...

BORSCHBERG

15? 15, 1-5 degrees, and he said it's really hard to control. Should we start looking for a helicopter just in case? I mean, first of all, I think he should be ready to jump, right, yes? Here we are looking for a bailout area in the area he's flying for the moment.

FREI (on phone)

If it's a pilot problem-- you know, pilot-induced oscillation, I think we should take time, do everything very calm.

NARRATOR

Unsure whether it's a problem with the plane or pilot error, the mission team performs a series of handling checks before landing.

PICCARD

No, now it's completely stable.

SCHLETTIG

Okay

PICCARD

...because now I can keep the heading without the autopilot.

SCHLETTIG

Okay, Bertrand, then the next thing, I'd like you to extend the outriggers and we slowly go down. (engines humming softly) (cameras snapping) (speaking in French)

REPORTER

How was the flight? It was fantastic flight. Fantastic flight. Any challenges or difficulties? Always challenges with an experimental airplane. You always discover, you always learn. The bigger challenge lies ahead. You have to cross the Pacific. Are you looking up to that challenge? Ah, yes, well, it's going to be really impressive, I tell you, to cross the Pacific, to cross the Atlantic.

BORSCHBERG

It's not done yet.

PICCARD

You can imagine that?

BORSCHBERG

It's not done yet. (crowd murmuring) This plane has the capacity to take the rays of the sun.

WOMAN

I got the chance to see this plane, and it's a once-in-a-lifetime moment. (crowd murmuring) Wow.

NARRATOR

After each flight the plane must be meticulously cleaned and inspected. Even minor damage could pose a serious threat. I think it's enough. (murmuring)

ROBERT FRAEFEL

We had a little delamination on one of the solar panels. No, don't push too much. No, it's perfect.

FRAEFEL

This white spot can overheat one of these individual cells. If one cell gets damaged, like with the light bulbs in a Christmas tree, you break down all the others, as well.

NARRATOR

To build the "impossible plane" required some unconventional thinking. Andr pulled together a diverse team of engineers from aerospace, Formula One racing, even elevator manufacturing. (beeping) A lot of time where we thought it would be impossible to finish the project-- it's too crazy, it's too hard. Over 13 years of design and testing, weight was the archenemy for lead designer Peter Frei.

FREI

I just knew from the beginning that it must be a super-light aircraft. 13 years ago, the thrill, "Wow, is it possible? Is it not possible?" And it was an up and down, you know, fighting, success, failures.

NARRATOR

What they ultimately came up with was a plane with a structure that's ten times lighter than the best gliders. More than 17,000 solar cells, each as thin as a human hair, make up the top surface of the wing and fuselage. These lightweight, flexible cells store nearly 50% more sunlight than solar panels on average homes. They built a skeletal structure that was largely hollow, like the bones of a bird, using carbon fiber three times lighter than paper. But there was one major design hurdle they'd have to overcome. Know exactly the capacity of a battery, it's a really difficult story, not only for us, for everybody who tries to implement batteries in a car or in a bicycle or something. To store enough energy to keep the plane aloft through the night, they calculated that the four batteries would weigh nearly 1,500 pounds-- a quarter of the plane's total weight. So every other component on board had to be lightweight and extremely energy-efficient.

BORSCHBERG

The efficiency of the electric motors, we have 97%. Only three percent of losses, and if you compare this with a piston engine-- the efficiency of the system is between 30%, 40%, maybe 45%. The engineers, the team, has done an incredible job. I mean, that's a Swiss watch of a size of a 747.

NARRATOR

With far fewer moving parts than an internal combustion engine, the four electric engines lose very little energy through heat and generate almost no friction. Like a smart grid, the network of solar cells connects to the four motors and batteries sitting behind the propellers. The cells capture the sun's energy and convert it into electricity, which flows through the grid to power the engines. Any excess charges the batteries. We charge the batteries in nine to ten hours and we extract the energy in eight to nine hours. So this is a very low rate, and that's why we have losses in the region of one to two percent. But with a power output only slightly more than the Wright brothers' first plane, the aircraft teeters right on the edge of flight. Failure is a real possibility, especially on the multi-day solo flights over the oceans. And both pilots had to train for the worst-case scenario.

BORSCHBERG

We never flew over the ocean five nights in a row. That's the main challenge. The last measure we can take is to bail out, but of course you want to bail out when you really have to bail out. If you do this mission, you have to be on the positive side, or you will never do it. Building the airplane, I think I'm realizing a dream I had when I was really a little boy, thinking about these pilots who were discovering aviation, these pioneers. I met Bertrand at the right moment with a great idea. Radar from Hotel-Bravo-Sierra- India-Bravo, good morning. I always have been a little bit rebellious against authority. I left home when I was quite young. What I learned as a fighter pilot which was useful, I think you are trained to better appreciate the risk, can come up with the right decision.

NARRATOR

But decisions are made on the ground, as well as in the air. To find the best possible route around the world, the mission control team pores over computer models and global satellite data. I am working on this since five years, so I was watching all the airports. There we have less rain, less windy conditions, less cloudy conditions. That's the reason that we will fly around the world in a tropical area during the dry season. Their route follows a broad tropical band around the Earth-- between the monsoons to the south and cold storm fronts in the north. (radio chatter) After leapfrogging across India to Myanmar, the plan is to get to China in time to make their first ocean crossing in early summer, when the hours of sunlight are reaching their peak. But no matter how much they map out beforehand, the pilots must be ready to change course at a moment's notice. (marching band playing) In places like Mandalay in Myanmar, the problem is that a hangar big enough to house the plane isn't easy to come by. So the team has to be self-sufficient. They came up with a waterproof, windproof mobile hangar that inflates like a giant bouncy castle. This 7,000-pound shelter takes the 20-person ground crew five hours to set up.

RYSER

On the ground, the aircraft has a lot of weak point. It is big, it is light, and therefore it is fragile. (machinery running) It's made of fabric, it's made of carbon, and you can break it with your finger.

NARRATOR

The five-day, solo Pacific flight will be the ultimate test, not just for the experimental airplane, but also for the pilots. If successful, it would beat the existing world record in any plane by nearly two days. Five minutes before departure.

MAN

Okay.

NARRATOR

In the lead-up to the mission, the pilots spent three straight days crammed in a flight simulator. While doctors monitored their brain waves and vital signs, they performed mental vigilance and stress tests. The long duration of the ocean flights is a concern for mission director and veteran pilot Raymond Clerc. Shut down engine number two and... And wait.

CLERC

This operation is really pushing the human performance to the limits. The airline pilots, they fly always two in the cockpits. You know, the normal flights, they last already 12 hours, and they can sleep during the flight. Our pilots, they don't have this chance.

NARRATOR

Because they'll be alone, the pilots can't risk falling into a deep sleep, which would make them too groggy to take over the controls in an emergency. (alert beeps) So the pilots practice a resting technique

used by the military and NASA

20-minute cat naps throughout the day, adding up to around three hours of sleep every 24 hours. (thunder rumbling) Now in Myanmar, it's nearly a month into their journey, and they are halfway across Asia. These shorter-duration flights serve as the final test as they get closer to the first ocean crossing. But first, Solar Impulse's safety review board must make a final call on which pilot will fly the critical leg to Hawaii. Bertrand's difficulty flying at night on his first flight to India raises doubts about his readiness during a mission control debrief meeting in Monaco.

FREI (on phone)

Now, Bertrand, I really would like to have more details on this phase before landing in Ahmedabad-- what happened there, because, you know, we had really some stressed situation on the ground.

PICCARD

I made a mistake in flying the plane in an unstable way, and I really scared everybody, so I was really, I was very embarrassed.

MARCUS BASIEN

Not being prepared good enough. Pilot condition must be better than what it was.

PICCARD

Now, of course, I don't have the same reactions than a jet plane pilot, so you also need to understand...

SCHLETTIG

No, which is not necessarily a bad thing. (thunder rumbling)

NARRATOR

While in Myanmar, the safety review board ultimately decides that Bertrand needs more training before making an ocean crossing. Andr is chosen to pilot the dangerous flight to Hawaii.

PICCARD (speaking French)

(horns honking)

PICCARD

I was extremely disappointed not to make the Pacific. That was my dream from the beginning. I think I underestimated the difficulty to fly it. On this airplane, it's not like in a normal airplane. You have to be really more precise. (sizzling) I initiated the project to fly in that airplane, but then the same time, it's true I'm not the best pilot. I'm the explorer who became a pilot. I had to learn to fly that airplane. And it's not easy for me.

BORSCHBERG

This decision was extremely difficult for everybody, huh? Especially when there are a lot of emotions and, and so much at stake. (horn honks) (horn honks) If I would do the Pacific, I knew that I had to prepare myself very well. (directional clicking) (birds chirping) When I will be in this cockpit, there will be moments when it will be too intense. We will sleep, but for very short time of 20 minutes' resting period. Yoga, meditation, breathing, it's a way to reboot the system, which is start to be congested. (jet flying in distance) When you fly jet fighters, you have whatever power you need to go against the winds, to fly in turbulence and bad weather. Here, it's just the other way around. This airplane is like a leaf pushed around by the wind. You have to make nature as a partner, and not as an enemy. I think that's an attitude in life. In some ways, I discovered when flying this airplane.

NARRATOR

From Mandalay, Solar Impulse moves on to Chongqing, China-- one of the largest and fastest- growing cities in the world. (audience clapping to orchestral music) ("Radetzky March" playing, audience cheering)

PICCARD

People say there is too much pollution, there is climate change, but it's not enough to complain about problems. We have to bring solutions. The same technologies that can make an airplane fly day and night with no fuel can be used to divide by two the emissions of CO2. (applause) After seeing this, I think in my future, my future job, maybe I will do something like this. We have to think about our children, our grandchildren. This thing is for them. (plane flying overhead) With Solar Impulse, we are only at the first phase. Our goal is not to transport passengers. Our goal is to transport a message. With Andr, we've done six legs from Abu Dhabi to here. Now it's time to go to the next level, and it's the ocean. This is why Solar Impulse is built. (propellers spinning)

PHILIPPE MANUEL

It's five days and five nights, solo flights over water. It's like going to the moon. Everything is under control, but you still have to go to the moon.

BORSCHBERG

The challenge with the solar energy is to fly through the night. The energy of the airplane is the critical factor. During the day, we climb very high altitudes, but we collect energy directly from the sun. And we use this altitude at the beginning of the night to slowly fly down-- this saves the batteries. Minimum battery charge is-- if everything goes on plan-- is not more than ten percent in the morning at sunrise. It's about an hour. So there is not much margin, huh?

NARRATOR

To conserve energy, the wings are designed for maximum lift, and to create a high glide ratio and low sink rate. If the engines were turned off at 28,000 feet, a jumbo jet would glide for 20 minutes, compared to four or five hours for Solar Impulse. They had to thread the needle of aerodynamic design. The larger the wingspan, the more energy they capture, but the more unstable the plane is in choppy weather. But if the wingspan were just ten percent smaller, they might not have enough energy to make it to sunrise.

MAN

Everything okay there? Okay, let's move forward.

DEMONT

We are removing each gram that we can in this airplane, because each gram of course is consuming energy.

BORSCHBERG

I did the most weight saving because I lost four kilos during the last four months there, so I did my contribution, huh.

FRAEFEL

We were never able to prove that the airplane can fly through the night, so far, and reducing weight is reducing risk. The lighter you are, the further you get. Who knows? I mean, maybe this is the minute which counts. Yeah, exactly.

TRULLEMANS

The Pacific is the largest ocean on the Earth. It's something that is always moving, developing, dying, depressions, typhoons. It's like a soup.

NARRATOR

Since Solar Impulse must climb over 25,000 feet each day, the weather team has to forecast 16 different layers of wind, humidity, and temperature. The most difficult part of this Pacific flight to Hawaii is the crossing of a classical cold front that acts like a wall-- cloudiness that gives precipitation, so all things that you have to avoid. And we have to find a hole in that frontal system. Every day, we are looking for a hole there. We're even dreaming about a hole. The hard part is that after three days, the reliability of their forecast drops below 70%.

DE TROYER

Flying to Hawaii takes five, maybe six days. When you cross that front, you have to be sure about details. And five days ahead, it's difficult, it's difficult to say. (wind rustling hangar)

REPORTER

Weather is posing a big problem for the Solar Impulse plane... The Solar Impulse has been grounded in China due to bad weather brewing over the Pacific Ocean.

MAN

Simon, the white.

DEMONT

If it happens that you have bad weather, pilot tired, and technology problem, there is the biggest risk we have. You dream of it almost all night, because if there is a failure, there is a person in there. So from the alt to end...

FRAEFEL

It's not only that we have the risk of losing the pilot, but it will also change the life of every engineer, which Andr maybe doesn't realize all the time. Yes, I can hear you, loud and clear. Yes. How much, how much?

BORSCHBERG

The closer we get now, more intense it is. How much, how much? The first time I will fall asleep will be over the ocean. We all know that falling asleep when you are stressed, not easy, huh? I mean, of course, if I end up in the water, it will be a shame, but I'm ready for a lot of things to happen. There will be moment of actions, there will be moment of reflection. I hope not moment of regret. This inner voyage is really what I'm looking for-- to go through these different experiences. This is the gift of all that.

PICCARD

You put breaking news, take-off tonight. Starting to be exciting. Finally. I'm getting emotional a little bit. Sorry. (voice

catching)

I'm so happy. Do we have a good corridor to get to the hole, or we do not have a good corridor to get to the hole?

ANGER (on speaker)

The hole's still there, yes, it is there. It's more or less confirmed. (speaking quietly) (speaking French)

NARRATOR

But a few hours later, there is a change. Take-off, we have cirrocumulus which are new. They were not seen before. High-altitude clouds that block sunlight have moved in around Nanjing and will reduce their energy right from the start.

ANGER

That front, that hole is moving a little bit to the east. I think, yeah?

NARRATOR

On top of that, tailwinds are decreasing. The flight is getting longer, and they'll have to cross the cold front later in their journey, when the forecast is less certain.

ANGER

What's the flight time? Flight time is six days and a half. Six plus. (whistles) Having a seventh day, it's not acceptable for me. If it's five-and-a-half, okay, on the edge. But if it's six and something, it's-- oh.

BORSCHBERG (on speaker)

I mean, if I look at everything now, I have the impression we are pushing a little bit too far there. We are at seven hours from departure.

ANGER

It's tight there, it's tight. And uncertainty due to energy. We have too many issues, that's the problem. We have too many issues now. Game over.

NARRATOR

After working around the clock for days on end, it's a huge blow to the team. They are exhausted, but they must keep going. The guys fighting each other because they are nervous, they are under tension, they are tired. If it's the window of the year, we just have to do it.

CLERC

We're not going to do it for tomorrow. I'm sorry, huh, but I think we'll not have a solution for tomorrow evening. The time to prepare a distance of such a huge window, the weather maps and so on, it's not done in three hours.

TRULLEMANS

He's tired, he's tired. They are tired. Don't forget that the distance from Nanjing to Hawaii is almost two times Europe, and then you're asking us, "What's the clouds going to be like in Poland and in Greece and in Ukraine?" In three hours? With two people!

DE TROYER

I mean... I like my job. I like my job. (laughter) But? But it was hell.

CLERC

I would prefer that we take some rest, and tomorrow morning we start to fight for the next one. Fresh and rested.

PICCARD

It worries me very much. If you look in the history of exploration, most of the big attempts have failed several times before the success.

NARRATOR

While the flight team waits in Nanjing, temperatures inside the hangar reach around 100 degrees. Lead engineer Robbi Fraefel is using portable air conditioners and jerry-rigged tubing to pump cold air into the battery compartments. Inside each of the four custom- built lithium-polymer batteries are 70 individual cells, laid out like squares of a chocolate bar, where the chemical reactions take place. The cells are similar to those used in mobile phones, but their chemistry has been optimized to boost performance. The challenge with batteries is that they rely on chemical reactions, which are sensitive to temperature.

FRAEFEL

A battery likes to stay always in the same temperature, same pressure, and if we change both all the time, it's not good for the battery. With every ten degrees higher temperature, the aging is about double. So it makes quite a difference. Only the Pacific flight will show the truth. All right.

NARRATOR

Working day and night shifts at mission control, they struggle to find a way through the front, running hundreds of computer simulations to come up with the best course.

CHRISTOPHE BEESAU

In the simulation, you play with the aircraft, you play with the possibilities of flight, like if it was a game.

There are many variables to take into account

weather, air traffic restrictions, and energy demands of both the plane and the pilot. From one simulation to another one you see things are moving, so it's not good. (plane engine roaring)

NARRATOR

After a month of striking out, the weather team finally sees their chance. There's a weak cold front five days out, but the team is confident that the plane can cross it.

DE TROYER

Is this now what we were dreaming of? We will have a nice corridor behind this system out to the ocean. Three, even four days flying in sunshine. (cheers and applause)

BORSCHBERG

Now it's the moment of truth. The first time that this airplane will fly with such a long time.

RYSER

Okay, we move. For the time being, looking good.

NARRATOR

With nothing but open ocean ahead of him, Andr will face 120 hours alone in the cockpit-- longer than any human has sustained before.

YASEMIN BORSCHBERG

He's doing this really with a lot of his heart and all his being. I don't think anything else matters. (plane humming)

REPORTER

The Solar Impulse 2 plane is currently tackling the most ambitious leg of its round-the-world journey. Once midway across the Pacific, there's no turning back, with no airports to land at and no boat capable of trailing the plane fast enough. Even to get one man across an ocean will push him and his machine to the limits.

PICCARD

We have now entered the first really critical part of the flight. He is now starting to reduce the power of the engines. He starts to glide down, and he needs to save his energy as much as he can until the next sunrise.

NARRATOR

During the night, Andr will slowly descend, relying on the potential energy he gained from altitude, and the plane's highly efficient glide. But at dawn, they'll be down to their last energy reserves. Just a thin layer of clouds could throw a wrench into all their energy calculations. And if Andr comes up short, his only option is the inflatable raft under his seat and the hope that his GPS beacon will guide a passing ship to his rescue. (talking quietly)

DE TROYER

Wednesday there is bad weather coming in, thunderstorms, and afterwards it's turning northwest. It's a... (whistles): It's a wall in front of us? And we have one or two layers where we have stratocumulus.

ANDREAS FURLINGER

We will reach the point of no return in approximately ten hours, so we have to have a decision by that point.

NARRATOR

They are fast approaching the point at which they can no longer turn back because of the prevailing winds.

PICCARD

The good side is that the plane flies well, Andr is in a good shape, and probably we can make it through the first night with enough energy. On the other hand, we're in deep (bleep), because we don't know how to cross the bad weather front in five days.

DE TROYER

It's a big deception, actually. The problem is that cold front over the ocean. And at take-off, we were confident we had solutions to cross it, and then we didn't have a solution anymore. (radio chatter)

NARRATOR

Andr has now made it through his first night, but the cold front predicted for day five appears to be intensifying and becoming more hazardous.

BORSCHBERG (speaking French)

(Furlinger speaking softly) So you can confirm that it's blocked now.

MAN

At that position, yes. At that position, yeah.

NARRATOR

The updated weather models now show that there is no clear passage through the cold front. Andr would have to descend through multiple layers of cumulus clouds, which likely contain moisture and will produce turbulence-- a dangerous one-two punch. The aircraft is going through all those clouds, not close, you know, with layers. But turning back to land also carries its own risks. Japan is their best option to divert, but they have no logistics in place for an unplanned landing. Andr is in a holding pattern over the Sea of Japan-- as they negotiate with several potential airports. Well, for me, it's clearly red to continue. It's no way. The earlier we announce this diversion, the higher is the rate of success, I would say, to save the airplane and the pilot and the mission. My personal opinion is that we have more risk of losing the airplane in Japan than if we try to reach Hawaii. I don't see how we can get permission to inflate a mobile hangar in Japan.

MARKUS SCHERDEL (on phone)

The airplane is not made to cross a front and fly in cumulus clouds. Until when can we still say we try to cross? Now. Either we divert or we take a big risk. (talking indistinctly) Nobody is confident to continue, so our position would be to make a diversion on Nagoya. (radio squawks)

BORSCHBERG (on radio)

If no window, no go. (radio chatter)

REPORTER

The green energy plane, Solar Impulse 2, stopped moving towards its make-or-break next destination, Hawaii. There's no telling how long they're going to spend in Japan waiting on the weather conditions.

NARRATOR

It is an unwelcome diversion. (wheels hit ground) A small emergency crew is now in Nagoya with the mobile hangar, but they don't have enough people to set it up. And the forecast calls for rain and heavy winds. (wind gusting)

BORSCHBERG (speaking French)

We need to be able to get the mobile hangar assembled tonight. If we did not succeed, the risk is that we lose the airplane completely, and the risk is extremely high. It's not a ten percent chance, it's 90. (wind gusting)

DYLAN GORTON

Well, what we need now is our hangar, you know, to prevent it from sun, wind, and rain. We're pretty much struggling to keep it on the ground. We need to put full speed on it. Maximum speed, maximum efforts.

NARRATOR

Just ahead of the rain, the rest of the ground crew finally arrives and jumps into action. (giving direction in French)

MAN

Un, deux, trois! (rain falling steadily)

RYSER

The aircraft was not just a little bit wet, it was completely wet, with water dripping from every single part of this aircraft. Well, we want to avoid a short circuit, because that would blow very probably the main fuse inside the battery. (water splashes)

SEILER

Oh, (bleep). I didn't see that.

PICCARD

I hope it will be okay, but I don't know at this stage. Maybe in three months we're still in Japan, and then it would be a disaster for our flight around the world. (rain falling steadily) (speaking French)

NARRATOR

The team is grounded in Nagoya for over a week to fix the wing spar that broke in the heavy wind and ensure the airplane is completely dry. Checking if there is a little bit of water left in the structure. Parts which have water inside explode if the water gets frozen when we climb very high. Andr would take all the risks. (beep) Yes.

FRAEFEL

We from the engineering, we want to reduce as much as we can to make his life safe, but he is a risky guy.

TRULLEMANS

No panic, no panic, no panic.

NARRATOR

Meanwhile, at mission control, the diversion to Japan poses a problem

for the air traffic control specialists on the team

a crowded airspace with many restrictions, which they have to negotiate.

NIK GERBER

Flying at 35 knots in the midst of traffic which flies at 500 knots. So it's a little bit an obstacle, huh?

NARRATOR

The Japanese insist that Solar Impulse avoid red zones of peak air traffic and militarized areas, limiting their exit strategy. We always want to wait for better windows, but now we have passed the 21st of June, and it's going to be worse and worse in term of energy. We are not on the safe side if we wait. In preparation for take-off, the ground crew begins taking apart the mobile hangar as the press stands by. (beeping) (panting) (radio chatter)

NARRATOR

But the forecast takes an unexpected turn for the worse.

PICCARD

There is no high pressure there. It's complete (bleep) weather. There is absolutely no way to go through. (sighs) To follow something for three days, and ten minutes before the take-off. Crazy. It was a bit... There's a really a problem somewhere in our way of working. (speaking French)

BORSCHBERG (on radio)

Okay. We're checking if we should proceed or not.

MAN

How are you feeling? Detached. That's the best way. (snoring)

TAMARA TURSIJAN

I think we really need it now, because the spirits are sort of not very well. And if we now take the plane back, assemble the mobile hangar again, and stay here for longer, it's going to be quite bad for the general mood of the team, I think. So that's why I believe we're going to take off. It's going to happen.

ANGER

This afternoon I was confident. Now I feel more like gambling. And if he has to bail out here, okay. The water's maybe already warmer, but I don't want to gamble with a pilot in the ocean. (speaking in French) I'm not confident to letting, taking the risk of your life. It's very difficult to go against the inner, inner feeling.

PICCARD

There are two terrible situations. The worst is to be in the middle of the Pacific and see that it closes, and to lose the plane and you jump. The other one is to be on the runway and to see that it closes, and this is exactly what we have, but it's not as bad as if you are in the middle of the Pacific. I feel that you went over the tipping point in terms of feeling, and so it must be right. But it's a terrible situation, and I imagine for you... (voice

breaking)

I'm so sorry for you, Andr. You... you cannot imagine... Don't be sorry, huh?

PICCARD

You cannot imagine how sorry I am for you. You are in that cockpit, you are ready to go. When I said we have to stop, Michael told me, "Thank you""

BORSCHBERG

Yeah. So confirm, flight is canceled. We go back to the tents, unfortunately, but that's-- that's life, huh? (talking indistinctly) A lot of hurdles. Big hurdles.

PICCARD

We tried everything we could. And we, we just... We just failed the last centimeter. The last centimeter.

DE TROYER

Always trying to make it, to make it work, and then you see that all that work is kind of for nothing. I have to admit that the last weeks, I was... I was losing, losing faith.

NARRATOR

With the Summer Solstice now behind them, the daylight hours and available energy to cross the Pacific are steadily decreasing.

BORSCHBERG

The monsoon is really picking up here in Japan, which means rain, it's also the risk of a typhoon. So what we are facing if we cannot leave over the next few days to Hawaii is being hit by a typhoon, lose the mobile hangar, and of course, lose the airplane.

SCHERDEL

We will always have an unknown thing. I think this is the nature of a forecast. It's a forecast, it's not the truth, yeah? Either we try to cross an ocean or not.

NARRATOR

At last, it looks as though they can. A promising five-day window of clear weather opens up from Nagoya to Hawaii. (indistinct chatter)

PICCARD

You know, it was so embarrassing to have Andr ready to take off, all the press watching, we had to cancel at the last minute. And this time we want to avoid this. (chuckling): So we're not telling anybody. And once we're in the air, if it works, then we say, "Hey-O, coco, here we are. This time it's going well." Okay. Third attempt, ladies and gentlemen. Third time that we try to move. (speaking

French)

Whatever happens, we go. I am committed. Completely committed to this flight. Point of no return is already passed long time ago.

GREGORY BLATT

Friday, we were both super-, super-depressed in Tokyo. This might be the end. And I'm, it's not sure we're going to still make it, but if we make it to Hawaii, at least we've done the hard thing. (talking indistinctly)

RYSER

We are just getting ready,

and we try to take off at 3

00 a.m. sharp. This time it seems better, so we try again.

CLERC

Looking fine from Nils. Go to standby now. (engine whirring)

NARRATOR

Then, just minutes after take-off, they hit a snag, this time with the plane's autopilot surveillance system, known as the M.A.S. (beeping) There was a short M.A.S. failure.

ANGER (on radio)

Okay, copy. There was a short M.A.S. fail. If we do not find out why it happened or what triggered it, we should not continue for the Pacific. The biggest concern is... The problem is the M.A.S. That's the, that's the killer one. (talking indistinctly)

PICCARD

The M.A.S. is the system controlling the autopilot, which is giving false alarms and waking up Andr each time he wants to sleep. (chiming)

NARRATOR

The M.A.S. wakes up Andr if there is a significant change in the airplane's heading or bank angle. (beeping) The false alarms are not just annoying, they keep Andr from getting the rest he needs. If the system fails completely, he will have to rely on mission control to wake him up. But there's a chance he could lose satellite communication out in the middle of the Pacific. So you want to continue to Hawaii? Yeah. Knowing that the monitoring is not working? Yeah. And you still... you... It makes life a little bit more complicated. We'll need monitoring from the ground. The risk is really high. The risk is really, really high. We have 55 minutes before the point of no return, and we don't know what is causing this, and we have no idea. I mean, it could degrade. (indistinct chatter)

FURLINGER

We still don't know the cause of the problem.

MAN

No.

ANGER

If we go back to Nagoya, I'm sure we would find another window, but the season is not over. A bloody (bleep) situation.

PICCARD

If we go back to Japan, I think it's the end of the project.

NARRATOR

With the electronics malfunctioning, the engineers have serious concerns about continuing. But the pilots are concerned about what another aborted flight could mean to the future of the project. (speaking French)

PICCARD

Now we just need to know if Andr wants to continue or not.

WOMAN

And what do you think it will take for him to decide? Guts. (chuckles softly) Not only as a pilot, but for the project.

NARRATOR

It's the most serious crisis they have faced, leading to a sharp division within the team. We have an aircraft,

which is not nominal. PICCARD

Yeah. Things will break during this journey, and if we start the journey already with one redundancy down, that's not a good starting basis. I would recommend to go back.

PICCARD

Going back to Nagoya in the season of typhoons with the possibility of destroying the airplane on the ground, in term of overall project, it's more risky to come back than to continue.

BORSCHBERG

Personally, I have a very good feeling I can do it. We have an airplane which has a very good source of energy. Very good storage.

ANGER

If you decide to continue, as a friend, you have all of my support, but as an engineer, I would say we have to go back as we have the choice.

PICCARD

A lot of people can be a little bit afraid, scared, by the, by the unknown in which we're jumping. I was very often in my life in these type of situations, and I tell you it's worth it. But the decision we take goes far beyond the flight itself. We have now the possibility to do what nobody has done. When Chuck Yeager broke the speed of sound, he had a broken rib. All these things were absolutely incredible feats.

FREI (on phone)

I think it's very dangerous, too, with this heroic speech to encourage people to take a wrong decision because we never have the story of those who got killed.

BORSCHBERG

This is a hard project. These are difficult situations. I guess I do it because I do this airplane quite well, and what can be done and what cannot be done.

FREI

Nobody in the future will understand that two managers can go against a whole team, and you really force us to support something that nobody wants to do.

SEILER

I just want to make one point very clear. There's only so much we can do to support you from here, from the ground. So when you decide to go on, you will be on your own up there.

ETTER

This is Capcom speaking. We have to start the climb now if we want to have a chance to respect the profile. Go! Climb! (engines humming)

BORSCHBERG (in French)

BASIEN

From an engineering point of view, it was the wrong decision. That you still can make it is, like, I don't know, driving with a flat tire. We have to be lucky, from a certain point of view. But it's... It's their decision.

PICCARD

We saved the project by deciding not to return to Japan. On the other hand, we have some of the engineers who are so pissed off because we did not follow their recommendation. They want to leave the project, and I don't know what will happen after Hawaii. (engines humming) (beeping)

NARRATOR

As morning comes, Andr continues to be awakened by false alarms.

BORSCHBERG

So I lost one source of information. Well, let's see, we are currently rebooting. A lot of wake-up calls in this, in this airplane.

SCHLETTIG

This M.A.S. system, which monitors the aircraft while the pilot is resting, is behaving erratic. We had it working in the beginning, then it produced a failure, so we shut it down. We tried again. (beeping) We don't really know what the status of the system is.

BORSCHBERG

The first night was about digesting, I mean, the emotion of the first day. It was really intense. When I look out, you know, I see the moon, I see the clouds, and here I am over the Pacific. I think a feel a bit higher. (talking indistinctly)

NARRATOR

On day two, there's a worrying new development-- the plane's batteries are overheating. We need to burn more energy. It is a risky game to...

SCHLETTIG

I know.

ANGER

Due to the flight profile we did on the first day, the batteries got too warm. If it sums up over the days, it can become really too hot. They can start to burn.

NARRATOR

Climbing too quickly on the first day increased the demand on the batteries, and they began to overheat. The risk is that this could degrade their performance.

ANGER

Today the challenge is to keep the battery temperatures low, as low as possible. So we will adjust the climb profile to not have too much current going into the batteries. (beeping) (talking quietly) It's turbulent since I think about one hour. (beep)

CLERC

We are climbing again at 9-0, and we'll see if it's better, but it costs energy.

BORSCHBERG

That's exactly what I was afraid of. Still some time until the next sunrise. (chuckles) Turbulences during the night, which means a lot of work, of course no auto-pilot, of course no sleep. I really started to work hard to see how we could get out. So we climbed again, and when you climb, you use the energy that you need for the night so it's a little bit stressful. (talking indistinctly)

MICHAEL MCGRATH

We're monitoring everyday how many resting periods is he getting. For the first two nights, he had three hours of sleep. That's okay, but we don't know what's going to happen on day four if you keep that rhythm, and day five. So we climb every day the equivalent of sea level straight up to Mt. Everest. No acclimatization. If you don't have enough oxygen, there's the risk of hypoxia. Within 60 seconds, will lead to a severe degradation in your ability to understand what's going on around you. You become euphoric. So not only are you in a dangerous situation, you're not able to recognize the situation and you feel good about not recognizing the situation. Then very quickly you will pass out. We're watching to see how his body is absorbing the oxygen. Is it actually getting enough? You're constantly listening to this... (imitating oxygen pumping) You hold your breath. (chuckling): And hope he breathes. And then you keep going.

LAILA FATHI

Pilot status. Mood, he is exhausted. Not as good as it was.

BASIEN

We have a pilot that is starting to show signs of fatigue. We have batteries that will not take a lot more abuse. We see that all the systems are stressed, yeah? The flight is not over.

SEILER

Quite intense. You have to perform because it's real-time, you know. As an engineer, you are used to, "Okay, I solved the equation today, "and if I don't solve it today, then I'm going to solve it tomorrow." And this is totally different. I'm kind of happy that it's soon over. (engine humming)

BORSCHBERG

So now a preparation for landing. I was thinking about all this, and I cried. Cried loud. It was a little bit ridiculous, you know, alone in the cockpit crying, everything was going well, but it was so, so intense.

ETTER

And Andr, you have some kind of headache?

BORSCHBERG (on radio)

No, not headache, but something has been growing on my head. Really strange. Okay, but I cannot see it. Do you have the face view? And now-- oh, okay. He looks terrific, yeah. (laughter)

BORSCHBERG

I don't know what happened. I spent too much time in this damned plane. (laughter) (phone camera clicks) (waves lapping)

BORSCHBERG (on laptop)

a va bien, a va bien.

ELA BORSCHBERG

He can feel every, I think, element in the plane. He knows which wings is vibrating. I think he was a bird in another life. (chuckles)

REPORTER

A plane powered only by sunlight makes history today in a five-day journey across the Pacific. This will be the furthest a solar plane has ever flown, as well as the longest-lasting solo flight in aviation history.

WOMAN

I've never been to something this historical before. Too young to see other things, just the right age to see this.

ETTER

It's absolutely beautiful, and the latest wind from the ground crew is 0-4-0-3 knots, in the axis.

BORSCHBERG (on radio)

Okay.

BLATT (in French)

To confirm, you have the landing and promotion lights on.

BORSCHBERG

It's nice to put them on. (cheering) Yippy!

ETTER

Flight path secure. Andr! (propellers winding down) (applause) (talking indistinctly)

PICCARD

(crowd murmuring) (singing) (speaking

French)

(applause)

BORSCHBERG

To fly with the sun, you need to be extremely energy-efficient. And this efficiency can be used everywhere.

PICCARD

This is why it's a historic first for aviation, and a historic first for renewable energies.

REPORTER

Will you make it around the world? Are you confident of that? It's an attempt. We cannot be overconfident.

BORSCHBERG

I received so much support from people I didn't know, and the beautiful message. So when you read this, you know, you know that people are supporting you. And I was carried by all this, I'm sure.

FRAEFEL

All of us were very lucky to have the pilot back, but when this decision came up that Andr and Bertrand want to continue, it hurt us in the soul that somebody decided against us. I was fully in opposition to Andr and Bertrand. Andr is pushing. We always had these discussions and fights, "Why do you tend to go beyond limits all the time? "We, engineers, tried to set reasonable limits "that you survive, "and you, your target is always to sort of prove us that we set the limits too narrow." If everybody is telling you that you are a hero, I think it's good also for them that there are people who try to pull them back and on the ground from time to time.

NARRATOR

Despite the divisions and problems with the plane, they are still hoping to get around the world this year. Their immediate worry is the health of the batteries. (beeping)

FRAEFEL

The concern about the batteries is that they are damaged. We heated up the battery in only one hour by about 20 degrees. At the moment, we are on the worst-case scenario where we have to exchange some cells in the batteries, which is... this is a nightmare.

PICCARD

We have overheated the batteries. More cells are damaged than the spare parts we have, so the logical consequence is that we will stay here until next April where we can continue. (gate clanks shut)

BORSCHBERG

The flight from Japan to Hawaii left scars on many of the engineers. (truck beeping) (drill whirring) I think, for everybody, to complete this flight around the world is extremely important. It's part of their life. I mean, they all stayed.

NARRATOR

During the break, new batteries had to be manufactured in Korea. The engineers realized that the batteries were over-insulated against the cold and heating up too much in warm conditions. So they engineered a two-way valve system that allows the pilot to let the heat out.

PICCARD

Last year, I was too much emotionally involved. a, c'est bon. I was thinking, "It's now or never." I was completely the head under the water, which is really not good for flying an airplane over oceans, you know? (speaking French) I've flown 20 days in a balloon, but we were two. Flying alone, it's something different.

NARRATOR

To prove he could fly safely over several nights, Bertrand trained to rely more on instruments than on the horizon. One, two, three, the fourth one.

PICCARD

I will never be as precise as a jet fighter pilot. This you cannot get at my age, but at least to do it correctly. Climb 174.

NARRATOR

After studying potential routes from Vancouver to Mexico, the team locks in on a three-day flight path to Moffett Field, home of NASA, just south of San Francisco. We see a weather window for Moffett right now. It looks good, it's a short flight. Okay? We'll only confirm really tomorrow, even on the day of take-off. It comes from the house of Charles Lindbergh, in Maui. A beautiful gift. This is more for the Americans than for the Europeans, and it's "Star Trek," Captain Picard, who is inspired from the twin brother of my grandfather. It was a challenge to be an explorer that would be different than my father and my grandfather, not to just redo the same.

MAN

The wind is at the limit, so for the time being, we don't go out.

PICCARD

I was doubting sometime, is it my way? Because I'm also interested by psychology, spirituality.

ETTER

Good Morning, Bertrand. This is Christophe. How are you? I'm fine. I had four hours of good sleep. I woke up before the alarm clock. I'm in perfect shape. Very good, very good.

PICCARD

My father and my grandfather gave me the drive to be an explorer, but my mother showed me the need to give it meaning. We were extremely close, like two human beings in quest of understanding why we were on this Earth. (radio squawks) Wonderful. Have a great flight, Bertrand, and enjoy it! And don't forget to come down!

MICHELE PICCARD

People are always thinking, I am the wife, I should have this fear. When Bertrand did his round-the-world balloon flight, our children were very small. At this age, children, they don't have any fear. They are just living the present moment, and I just realized I should not give them this fear.

CLERC

The flight is long for him, huh?

This was one of his main question

If I don't sleep, how can I survive?

PICCARD

First sunrise over a sea of clouds. That's the sunrise I will remember all my life. (toothbrush swishing) (chiming) Switching on the solar generators. I can show you my little house. That's the kitchen where I prepare my food. The toilet inside the seat. That's the cellar. Breakfast.

The family

Estelle, Oriane and Solange, Michle.

PICCARD

BAN KI-MOON

Hello. Hello, Solar Impulse, hello, Captain Piccard.

PICCARD

Good afternoon, Mr. Secretary-General. I speak to you from the cockpit of Solar Impulse in the middle of the Pacific, flying on solar power. All this airplane is like a smart grid, collecting energy, distributing energy, with very, very high efficiency. And this is exactly what the world needs.

BAN

Wonderful. You look like an astronaut in the moon. Thank you, Mr. Secretary-General, and congratulations for what you are doing. The world will remember it. While you are making history, we have also made history today. More than 175 countries signed the climate change agreement. Thank you for your leadership and inspiration. All the best to you-- bon voyage. (applause)

PICCARD

I think I had more butterflies in the stomach before that live transmission than when I took off with Solar Impulse three days ago. The sun's going to arrive in a few minutes to carry me to San Francisco. (voice

breaking)

It's beautiful. Moment extraordinaire.

PICCARD

14 last years of attempts, of setbacks, of problems, it was worth going through all these moments just to be here, now. Il est o, Stphane? (wheel hits ground) (speaking French) (laughter) (man speaking French)

ALAN EUSTACE

The thing that amazes me is the size, and especially given the low weight. This is the moment where you start to see electric power taking off. (speaking French) (applause) (cheers and applause)

PICCARD

Sometimes, you know, there are people who will say, "Why do you fly with a solar airplane "like Solar Impulse? "It's expensive, it's big, it's slow, only good weather and only one person in it." Silicon Valley, nobody ask. Everybody knows, understands. When Solar Impulse landed yesterday in Phoenix, it was just in front of a cemetery of old airliners.

BORSCHBERG

It's very sad. A lot of these airplanes will never fly again. You know, they get dismantled. This one lost, you know, the left eye. Crazy. Of course, it's normal. All this will be replaced by better technologies. But still, in fact, I feel emotions when I'm here. An airplane is not just a piece of metal. It represents much more.

PICCARD

When people think fuel is forever, they forget the Gold Rush 100 years ago, and the ghost towns. I'm not saying Solar Impulse will replace an airplane like that very soon. In ten years' time, we have airplanes flying electric with batteries, plugged in the grid before take-off, and they will transport 50 people. Today you make electricity with solar panels in Dubai cheaper than with gas. Ladies and gentlemen, you are now doing your last flight on the combustion-engine airplane. In the future, you will be flying electric.

NARRATOR

At mission control, there is no time off.

The team has one focus

getting across the U.S. as fast as possible so they can cross the Atlantic during the peak energy days of summer. They will have to navigate around the turbulent air over the Rocky Mountains, the unstable thermals of the Southwest, and the Midwest's infamous Tornado Alley.

DE TROYER

Well, we arrived in the tornado season. Every two or three days there are thunderstorms, and those thunderstorms, they can lead to tornadoes. (birds chirping)

MAN

The local news came on and said this was landing, so I went outside and watched the skies to try to see something weird. All night long. I don't buy into the global warming deal, just to be honest. We've had oil and gas for all these years. But if they can make stuff battery-powered, then I'm all for that. They can obviously make it go faster. Because I think you can drive faster from Phoenix to Tulsa than he flew, but it's a start. (applause)

REPORTER

Just as the Wright brothers did before them, this team hoping to show anything is possible with the right resolve. (crowd murmuring)

NARRATOR

But in Dayton, Ohio, a problem with the mobile hangar reminds them just how fragile their plane is. Today, we had a failure in the electric system of the mobile hangar. It deflated. Touched the airplane, it can destroy the airplane, huh? (talking indistinctly)

RYSER

The mobile hangar was laying on the tail of the aircraft, slowly going down onto the wing. I just would like to hear if there is a visual defect. We have no idea what, especially here, I'm not so afraid, but from the wing.

PICCARD

Until we see there is a problem, it's stupid to cancel the flight of tomorrow. Don't even think about it. I hope we can fly again. I think that's where we are.

NARRATOR

Even though there may be no signs of external damage, the weight of the collapsed hangar may have cracked the plane's internal structure.

BORSCHBERG

What we try to avoid is that we get into a panic stage. Bertrand is pushing, of course. (discussing in French) Don't push this. Don't push, this is not the moment. We try, we go step-by-step. So for me, for me, it's a non-event. It's not a non-event, yeah? Be careful what you say. We are in deep (bleep). In really deep (bleep). Maybe there is nothing on the airplane, but we don't know. (talking indistinctly) This is an airplane which is certified to fly over the major cities, and you don't play with safety. That's the responsibility of the engineers. And I don't think we'll come with an answer which is black and white.

NARRATOR

To be sure the plane has no structural damage, they must calculate the suspected load on the tail and wing.

PICCARD

This project is too big to be run just by personal wishes, but this is very new for me.

NARRATOR

After crunching the numbers through the night, the engineers finally decide that the plane is safe to fly.

BORSCHBERG

We had a couple of explosions, very often because of our character, maybe because of our egos. And it was a hard process. I think we understand that we bring to each other much more than the difficulty that the relationship creates.

PICCARD

I don't think we're ever going to laugh at the difficult moments we went through. With Andr, we are together since 13 years in this project. We're very proud that we didn't split apart, that we didn't have any divorce. That we could learn so much from each other.

NARRATOR

As they arrive in New York, Bertrand is reminded of the triumphs and struggles of his father, Jacques Piccard.

PICCARD

In 1969, my father arrived with his submarine. After the drift mission of one month in the Gulf Stream, he arrived in front of the Statue of Liberty. I was 11 years old, so happy and proud. You know, altogether, he had 50 projects of submarines, and only five got some fundings. I saw my father worn out by all these disappointments. He told me, "Don't feel obliged to continue my work." (ship's horn blowing)

NARRATOR

Now the Atlantic Ocean looms large. Bertrand faces perhaps the biggest challenge of his career. It's smaller than the Pacific, but with notoriously harsher weather. There's a cold front in their way-- a wall of clouds and unstable air that's risky for the airplane. After days searching, mission control in Monaco notices a narrow corridor of clear skies starting to form, leading to Sevilla, Spain.

DE TROYER

The corridor that we've been following, and that's really, it's really small. Between all the bad weather to the north, to the south.

NARRATOR

But they only have so much time before it closes. (Velcro ripping) Let's go for the Atlantic, my friends. (cheers and applause)

PICCARD

The Atlantic is going to be probably the greatest flight of my life. I don't want to put the pressure and say, "Oh, I met Charles Lindbergh when I was a child," and imagine how important it is and how symbolic it is. I want it to be natural. I want it to happen in a peaceful way. When you are in the middle of the unknown, you have these moments of grace. You are, at that moment, like you would like to be forever.

CLERC (on radio)

So now you are challenging your fighter pilots.

PICCARD (on radio)

I love my fighter pilots. (laughs) Did I show you my map already? Maybe Andr will not like this map as much as me because the Pacific is very small on this map, but the Atlantic is very big. (laughter) In front of you, the window is still open. Behind you, the window has closed.

NARRATOR

Bertrand makes it through the corridor just in time. Next, he must harness the powerful winds of the Jet Stream to propel him towards the coast of Spain.

TRULLEMANS

Jet Stream is the conflict between cold air in the upper levels and warm air, and they are pushing against each other. At 20,000 feet, we may have 50 to 60 knots pushing the aircraft to the east to Europe. And now we will fly very fast, huh?

REPORTER

An airplane powered solely by the sun has made aviation history after an almost three-day flight across the Atlantic from New York. From Seville, the aircraft will continue its journey back to Abu Dhabi, where it all began for this extraordinary project. (fighter jets roaring)

BORSCHBERG

When I flew yesterday over the pyramid, they were just emerging out of the haze. I guess it was exactly the same as they were 4,500 years ago. They believed in eternal life, and for me, it's a symbol of eternity.

Solar Impulse is also intended to be a symbol

a symbol about sustainability, a symbol about the potential of renewable energy. If you build something like this, which is done to be forever, it's not necessarily the solution which we would go for. Sustainability means that you stay in line with nature. And I'm not sure in fact the way we build takes this into account. If you don't change the situation, the world will dictate you the future and not the other way around.

PICCARD

There are so many mixed thoughts and feelings right now that it's difficult. After this flight, it's over, so it's like a family that's going to split. But there is the message, and what we have to do out of this flight, and I'm working since years for that, and for that moment, and I want to be sure not to waste it. (talking indistinctly)

NARRATOR

After 16 months and nearly 25,000 miles, the last leg to Abu Dhabi presents an unexpected final challenge. They knew it would be hot in this desert region, but now an extreme heat wave is posing a dangerous threat.

TRULLEMANS

We never flew with such a light aircraft in such conditions. Extreme conditions. (sighs)

NARRATOR

Above the Saudi Arabian peninsula, night temperatures at 3,000 feet hover around 90 degrees. Mission engineers worry that critical systems on board, which are not certified for such heat, could completely shut down. But their bigger concern is energy. As the hot air cools during the night, it creates strong downdrafts of wind that push the plane to lower altitudes. I didn't expect such an issue at the end, with the last leg. The downdrafts are so strong that he cannot fly through the night. He will use so much energy to stay at this level that he cannot survive during the night.

ETTER (on phone)

Take-off conditions on Sunday are not good, and we will have extreme thermals overhead. I believe that each of the problems can be solved.

FREI (on phone)

There is a danger that you overheat equipment, and at the end, you have a failed aircraft.

NARRATOR

After several days waiting, the severe downdrafts appear to be subsiding. It looks like the flight is back on.

ANGER

As we are quite tight on energy, timing is critical. Every day there are cumulus clouds that are really, really high. Is the, is the pilot healthy? This time the pilot is a little bit green, I have to say. (chuckles softly) You mean it's stomach problems, or...?

PICCARD (on phone)

Yeah, yes. I'm a little bit weak, but the general... General situation is good. Okay, then drink a lot of water, but you're the doctor, not me.

MAN

Keep in mind that the flight is not easy.

ANGER

Yeah. No, it's a difficult flight. I know. Absolutely.

PICCARD

Everything is different from what we have planned. (laughing) It's adventure. It's not a business plan. Nicolas Lugeon. (man responds) Claude, Staub, Jerome, Paige, Eoin.

MAN

Bertrand, are you okay? (speaking French) It's not the moment I'm the healthiest in my life, but it's still under control. Still under control. (speaking French) (speaking French)

BORSCHBERG

PICCARD

I hope it's the last taxi. Because if it is, then it's fantastic moment right now. I've never been in a project that gave as many moments of elation and moments of disappointment. It's really strange. (man speaking French) (engine whirring) (applause) It's really difficult. (speaking French) As we told you, the night might be quite tough for you.

PICCARD (on radio)

I would like to drink, I would like to pee, I would like to hopefully re-evaluate my clothing because I'm too hot, but I just can't do anything else.

NARRATOR

During the night, Bertrand must try to ride the updrafts and avoid the downdrafts that will sap his energy reserves.

JULIAN KRONERT

Once you have an updraft, just go with it, and don't fight the downdraft with power. Just let it go. It was not such a bad idea that you had 17 years ago, huh?

PICCARD (on radio)

You know what, it became a good idea thanks to all the people who supported it.

SEILER

We can't save the planet with one plane flying around the world, but maybe it inspires many people to start solving problems instead. Then maybe it was worth all this stress. We are late. We really have to move, gentlemen. How you will enter? I don't have a... You don't have a permit to enter. I will go, I'm the pilot. I tell you I will go. You can shoot me, I will go and I will take my team.

PICCARD

When Andr took off the ninth of March last year, I was thinking, "We are completely crazy." And a year and a half later, you see the result of what our team has achieved because they accepted to dream. And when you see the state of the world today, it is a crime not to try something. Not to try to increase quality of life on this planet. We love to fly. For others, it's an art, in science, in the community, but we have to try. What I remember is to be on this runway 15 months ago exactly at this position, ready for the flight around the world. Not knowing what will happen, not knowing how much time it would take, just go. Just go and start. And seeing the airplane coming, it's like slowing down the time. It's really, really strong.

BORSCHBERG

Whoa, God, we did it! Wonderful! (cheers and applause) (cheers and applause) (cameras clicking) (speaking

French)

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