Inside the First Solar-Powered Flight Around the World

View from the cockpit of Solar Impulse 2 as the plane heads for landing in Abu Dhabi. (Solar Impulse)

View from the cockpit of Solar Impulse 2 as the plane heads for landing in Abu Dhabi. (Solar Impulse)

In the wee hours of July 26, 2016, Solar Impulse 2 landed in Abu Dhabi to eager crowds and cameras. After 14 months of travel and 550 hours in the air, the plane had accomplished what many had deemed impossible: traveling 25,000 miles around the world—over four continents, two oceans and three seas—without a drop of liquid fuel. The sun’s vibrant rays supplied the craft’s only power.

Now, a new NOVA documentary, The Impossible Flight, airing tonight on PBS, dives into both the challenges and the triumphs of completing this harrowing trip around the world, giving audiences a taste of the passion that drove the Solar Impulse team, and their soaring optimism about the future of energy.

Solar Impulse is the brainchild of Bertrand Piccard, a psychiatrist and explorer who came up with the idea after his 1999 nonstop spin around the world in a hot air balloon. During that venture, he watched his fuel level drop day after day, worrying if he’d have enough, which left him wondering if there was a better way. Eventually, he figured it out: lose the fuel.

Piccard reached out to potential partners in the aviation industry, but was met with resistance.  “Everyone said it was impossible,” he says. “[They] said I was just dreaming.”  In order to have enough solar panels to power its propellers, the plane would have to be massive—but at the same time, extremely light.

So Piccard turned to the Swiss Federal Institute of Technology where he connected with André Borschberg, an engineer and entrepreneur who trained as a pilot in the Swiss Air Force. Borschberg was consulting for the institute (which he describes as “The MIT of Switzerland”) and was intrigued by Piccard’s idea. The pair officially announced the project in 2003.

“When you announce officially,” says Borschberg, “there is no way back afterwards. And [so] that’s what we did for the next 13 years.” The duo reached out to investors, engineers, industry partners and more to develop the plane. Every component was tested and optimized, right down to the glue binding the carbon fiber structure.

The result of all of this work, Solar Impulse 2, is certainly a feat of engineering. The plane boasts a wingspan larger than a B-747 jumbo jet, but only weighs around 5,000 pounds, which is comparable to an average family car. A staggering 17,248 photovoltaic solar cells—each one roughly the thickness of a human hair—blankets the delicate wings and fuselage. These cells bask in the sunlight, charging the plane’s four lithium batteries to keep its propellers spinning through the dark nighttime hours.

Piccard and Borschberg traded off flying the plane for the 17 legs of the venture. Each slept only in short intervals to tend to the plane’s demands. Its wings couldn’t tip more than five degrees, otherwise the craft might spin out of control thanks to its low weight and expansive size. This airy construction also meant that even a small spot of foul weather or winds would easily whip the plane off course.

As the documentary details, weather became the team’s biggest foe. Because the plane travels on a sinuous path—climbing to nearly 30,000 feet elevation during the day but slowly descending to roughly 5,000 feet at night to save energy—the team has to forecast wind, humidity and temperature at multiple elevations. And the swirling weather system is constantly evolving and changing. Weather conditions delayed their departure from China, later forcing the team to abort their initial Pacific crossing and land in Japan. But then more foul weather began to churn over the Pacific, causing two canceled departures.

Tensions rose as the schedule was continually pushed back—but the crew was also well aware of the consequences of pushing through weather or technical difficulties. “If there is a failure, there is a person in there,” one of the team’s crew says in the documentary.

Though there were many bumps along the way, the strong convictions of the Solar Impulse team helped them navigate these challenges. “I never lost faith in what we were doing,” says Borschberg. “There was something which told me always that there is a solution somewhere. It took more time, it took more effort, definitely...but ultimately we always find a way.”

But a plane can’t fly on convictions alone. Creativity, and thinking outside of the aviation industry, was also vital to their success, says Piccard. Many aviation experts seemed to have become limited in their thinking, blinded from past experiences of how to build a flying machine. Instead, the duo turned to shipyards, chemical companies and more to seek out potential materials and solutions for their aircraft. The ultra thin carbon fiber that makes up the body of the plane, for instance, was created by the same company producing hulls for the sleek sailing boats the European Alinghi team race in the America’s Cup.

“We couldn’t develop new solar cells, new batteries, new motors,” says Borschberg, noting there just wasn’t time to rethink every technology they used. Instead they found the cutting-edge solutions already out there, repurposing them for flight, he says.

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