ABU DHABI, United Arab Emirates—Early on Monday, if the desert wind rushing toward the Strait of Hormuz lays down and dawn comes in clear and bright, a very large and odd-looking experimental aircraft will lift off from a military airport in Abu Dhabi, turn east toward the rising sun, and take a run at history.

On board will be a single pilot, for the cockpit is too small, and too cramped, to carry more. He will steer through morning quietly and quite slowly—faster than a running man, but far slower than, say, a Vespa scooter driven by a guy who's late for work.

From below, his aircraft will resemble a toy, with enormous, stiff wings jutting out of a short, thin fuselage, and stabilizers at the tail that are as blunt as pegs on a pogo stick.

As the plane begins to climb, almost imperceptibly, the impression will be of an object set adrift more than one purposefully driven. By contrast, almost any aircraft it meets, even certain thumb-toggled drones, will seem like overachievers.

With altitude, however, the plane comes into its own. Seen from above, in thin, calm air, its lines suggest an albatross or a condor, strong of shoulder, built for distance. And the reasons for the craft's oddity become clearer, too: Nearly every sun-facing surface, from wingtips to rudder, gleams with blue-black photovoltaic cells. The plane is called the Solar Impulse 2, and the Swiss explorers who built it, Bertrand Piccard and André Borschberg, intend to be the first to fly around the world propelled only by the power of light.

Heading first to India, next to China, and then on to the United States, their journey will last some five months, with many stops along the way. During the longest legs of their flight, over the Pacific and Atlantic Oceans, the men will remain in the air for days, beyond reach of runways, islands, or easy rescue. They will face dangerous, unpredictable weather over wide-open water, same as a host of earlier adventurers, many of whom never returned.

The goal, though, is not speed or risk but technological and entrepreneurial statement. Built almost entirely of custom-made, ultralight carbon, with advanced batteries, solar cells, and electric motors, the Solar Impulse 2 will be able to do what has never been done by a piloted, light-powered craft—stay aloft through the night, across vast distances over land and sea. It is, in theory, a plane that might fly forever.

"The airplane is special not because it is solar, but because it is efficient," Piccard told me recently in a cavernous hangar on Abu Dhabi's Al Bateen airfield. "It is efficient at harnessing energy, at storing energy, and at using energy."

View Images Planned Route of the Si2 The planned route of the Solar Impulse 2, which will spend an estimated five months circumnavigating the globe, making stops in the cities shown here. NG maps; Source: Solar Impulse

Outside the hangar a jet rolled loudly past, battering the windows with dust and boiling fumes. Piccard took the cue and said, "My plane will never do that." He smiled toward the Solar Impulse 2, sitting behind us, gray and delicate, suspended in a steel cradle. "What we have here," Piccard said, "is the future."

Becoming a Visionary

Piccard, a psychiatrist by training who regularly practices self-hypnosis, often uses "future" to describe a kind of hyper "present," not something that will arrive one day but that is available now, in progressive stages of discovery.

If this sounds a bit cliché, Piccard will only draw encouragement from your doubt, just as he did 12 years ago when many experts in the aviation industry said his plans for a 21,000-mile (33,800-kilometer) light-powered flight were impossible.

Piccard is of average height, slender and fine-boned with blue-gray eyes and impressive posture for a man who has spent so much time wedged into flying machines. He is the son and grandson of explorers who, during the past century, broke records while investigating the ocean's depths and the atmosphere's heights using submersibles and balloons they designed themselves.

When he was a boy, his family lived for a time in West Palm Beach, Florida, near Cape Canaveral, while his father, Jacques, worked with the U.S. Navy. Jacques's friends and associates included rocket scientist Wernher von Braun and many others involved in the American space program.

View Images Bertrand Piccard, a psychiatrist by training, sits in the cockpit of the Solar Impulse 2. Raised in a family of famous explorers, Piccard says he hopes his flight will raise awareness of what's possible with solar power and other alternative energy solutions. "Clean technologies are therapy for the planet," he says. Photograph by Philip Cheung, National Geographic

Neil Armstrong and Buzz Aldrin, the first astronauts to walk on the moon, visited the Piccard home. Another astronaut, Scott Carpenter, dropped in at Bertrand's 12th birthday party. Piccard said he learned not to ask too many questions of the astronauts, who had wearied of the constant inquiry of strangers and the press. Instead, he says, he simply listened. The past century's greatest adventurers wandered, unguarded, through his living room. Why should he interrupt?

"I only ever asked Neil Armstrong one question about the moon," Piccard said. It was years later; the men had become friends. "I asked, 'Did you receive any kind of psychological training, anything to prepare you for such a huge thing as being first man on the moon?'"

Armstrong said no one had ever asked that before. "No," he told Piccard. "I was a test pilot. We didn't talk about stuff like that."

Piccard, for his part, always talks about stuff like that. To him, the spiritual and emotional elements of exploration are important—as ends in themselves, and as components in his public persona. In conversation Piccard often gusts into the romantic, describing his goals and adventures with vigorous, over-the-top words and phrases (for example, on his own website, he refers to himself as an "inspioneer"—a made-up term that, one guesses, would have made Armstrong cringe).

The leaven does settle, in quiet moments, during which he comes off mostly as very curious about the world, and particularly interested in "how people decide to become what they are, and how they decide what is possible."

View Images Bertrand Piccard (left) and his father, Jacques, stand beside the Ben Franklin, a submersible Jacques designed. In 1969, Jacques Piccard and a team of researchers lived underwater for a month aboard the Franklin, traveling from Florida to Nova Scotia while conducting oceanographic research. Photograph courtesy Solar Impulse

Growing up as he did, awash in a jet stream of adventure, you might forgive Piccard's lush language and his interest in the inner workings of the human mind, which would lead him to a career in psychiatry. He said he recognized within the field an opportunity to "explore the human soul" while helping others along the way.

For years he maintained a private practice in Switzerland, becoming a proponent of self-hypnosis as a tool for transformation. Personal choice was a big theme, along with its inverse: the ability to un-choose.

"We can always make changes," he said. "We just have to become aware of the option."

Can I Fly Forever?

From this flexible perspective there is perhaps nothing unusual about deciding to be a visionary and then setting out to make it true.

In his teens, Piccard launched himself from hilltops in hang gliders; in his 20s, he began flying microlight aircraft. Later, in addition to his medical practice, he took up hot-air ballooning, after the tradition of his physicist grandfather, Auguste (who was so well-known in his day that he provided inspiration for the character of Professor Calculus in the Tintin comic books).

This path eventually led Piccard into ever more exclusive circles of aeronautical exploration, complete with corporate sponsors and millionaire rivals such as Richard Branson and the late Steve Fossett. Piccard competed against both men, at different times and over the years, as each sought to become the first to circumnavigate the world in a gas balloon without stopping.

Twice Piccard failed, but on his third attempt, in 1999, he and co-pilot Brian Jones floated around the globe in 19 days aboard a custom-built craft called the Breitling Orbiter 3. Their balloon was kept aloft by propane and helium, and though the men brought with them some four tons of gas, suspended from their craft in long, silver cylinders, it almost wasn't enough. Stressed and weary near the finish, with his previous ditches haunting him and all but one gas tank empty, Piccard feared he'd fail again. He became obsessed with fuel.

"Fuel is limitation," he said. "I don't like limitations. I wanted to be able to fly forever."

View Images Auguste Piccard, Bertrand's grandfather, is shown delivering a physics lecture. In the 1920s and '30s, Auguste, a physicist, conducted atmospheric research from hot-air balloons and later designed a pressurized capsule that he used to reach the stratosphere. He was so well-known in his day that Belgian cartoonist Hergé was inspired to model a character after him—Professor Calculus in the popular Tintin comic books. Photograph courtesy Solar Impulse

Like many scientists, astronauts, and others who have spent time at great heights, Piccard also became impressed with the apparent fragility of the nations and cities, islands and seas passing below him. He said that during nearly 500 hours in the balloon, he began to wonder how exploration might meet the challenges of climate change and rapacious development.

Though he refuses to associate himself with the so-called "green" movement, this question, along with his growing disdain for fossil fuel, was revelatory. While still aboard the balloon he glimpsed the shape of his next adventure: He would circle the globe again, in a solar-powered craft. Free of fuel, he could prove what was possible using technologies that hadn't been available to his father, grandfather, or their friends—clean ones.

"This isn't about oil, and it isn't a movement to deprive people of things," he said. "Climate change is always presented as a battle to protect nature against business and comfort. Ecologists have put nature before humankind, and that's a big mistake, a false equation. These technologies are available now. We can change the way the world works, not by making people's lives smaller, but by making them bigger."

In 2002, Piccard began searching for allies and experience. He researched alternative energy and traveled to the U.S. to meet with aviation pioneers such as engineer Paul MacCready and Burt Rutan, who designed the first plane able to complete a world circuit without refueling.

View Images In 1999, Bertrand Piccard and co-pilot Brian Jones lifted off from Château-d'Oex, Switzerland, in a gas balloon named Breitling Orbiter 3. Nineteen days later they became the first to circumnavigate the globe in a balloon without stopping. It was during this journey that Piccard says he came up with the idea to repeat the feat in a solar-powered airplane. Photograph courtesy Solar Impulse

A year later, Piccard presented his solar vision to the Swiss Federal Institute of Technology, which agreed to undertake a feasibility study. To lead it, the institute chose André Borschberg, an engineer, businessman, and former fighter pilot in the Swiss air reserves. The study group decided Piccard's idea was possible—though beyond reach of the day's technology.

At the time, solar cells, ultralight airplanes, large-capacity batteries, and electric motors were well established, if not yet widely used. Several solar aircraft had been built and flown successfully, including manned and unmanned models—some of them massive—designed by MacCready's company, AeroVironment.

But they were all extremely fragile, and none of them achieved flight for days with a pilot onboard, or faced down the many hazards of crossing oceans. Illustrating the dangers, one of Solar Impulse 2's predecessors, a 23-foot-long (70-meter) unmanned craft named Helios, built by NASA and MacCready, broke up and plunged into the sea when it encountered strong winds during a flight off the Hawaiian coast.

View Images Emily M. Eng, NG Staff. Sources: Solar Impulse; U.S. Energy Information Administration

All of these challenges, along with Piccard's enthusiasm, enthralled Borschberg. At the conclusion of his investigation, he joined Piccard to found the Solar Impulse project. Not long after, they began designing a plane from scratch.

Sitting on a Toilet at 28,000 Feet

"Libellule," Borschberg said, the French word round and light in the dim, cavernous hangar. He was thinking his way through a bestiary of flying creatures. "I don't know how you call it in English?"

Dragonfly: this is what Borschberg sees when he looks at the plane he has built. He did not begin with insects in mind—military aviators tend toward raptors—it's just, Borschberg says, what happened.

"It is so light, the wings so long, with this little cockpit head. And, you see, it is very slender. It had to be."

If Piccard is the visionnaire behind Solar Impulse, Borschberg is the project's tactician, able to translate ideas into action. He was responsible for gathering many of the team's engineers and designers and for laying out a corporate plan.

Borschberg is lean and tall, well over six feet (1.8 meters) and just under the maximum height for pilots in the Swiss military. He has spent years shoehorning himself into airplanes designed for smaller people. In the near future, Borschberg will exceed any previous span of discomfort when he slides into the single seat of the Solar Impulse 2 and flies continuously, sometimes at an altitude of 28,000 feet (8,500 meters), over the Pacific, where there is no place to land and stretch. Or relieve oneself. Or make repairs.

The journey will be divided into 12 legs, and the men will stop frequently to rest and trade off piloting duties. At each landing zone a support crew will meet the plane, and the pilots will promote messages of clean energy and innovation to local audiences.

Even with these regular pauses, the legs will often take a dozen hours or more of flying, and at least three legs—from China to Hawaii, Hawaii to Arizona, and New York to Europe—will last up to five days.

View Images André Borschberg, an entrepreneur and former fighter pilot in the Swiss air reserves, founded the Solar Impulse project with Bertrand Piccard in 2004. "The aviation world did not have the technology to build this," Borschberg says. "So we had to bring all of these things together to do it." Photograph by Philip Cheung, National Geographic

During those flights the solitary pilot won't be able to stand up (there isn't room), though he can recline the seat, which also doubles as a toilet. Imagine a lounge chair stripped of its padding and crossed with a port-a-john. Now sit there for days, mostly belted in, often very cold, never getting up. Try to remember that the view will be inimitable.

Human comfort during long, exhausting flights was one of the first problems Solar Impulse engineers faced, and it's often one people ask about. (The idea of flying a plane while sitting on its toilet is either incredibly amusing or horrifying. "What if you crash?" someone asked Borschberg, thinking of the waste storage tank below the seat. "I hope we don't," he replied.) The history of adventure shows that comfort routinely falls aside before other concerns. In this case it was a balance between surface area and weight.

Building a Dragonfly

View Images The Solar Impulse 2 glides over Payerne, Switzerland, on its first flight in June 2014. The plane's tiny cockpit has room for only one pilot, and during their flight around the world Piccard and Borschberg will trade off flying duties—sometimes staying aloft over open stretches of ocean for up to five days at a time. Photograph by Jean Revillard, Solar Impulse

Solar Impulse engineers knew they needed a lightweight airframe. A large plane needs a lot of thrust to get it off the ground and keep it moving forward. Even using the best available technology, solar-powered engines are weaker than gas-powered ones and offer less thrust. Heavy was not an option.

Earlier experiments with solar aircraft had shown that long, wide wings were also required to help the plane rise and glide more effectively. But larger surfaces are inevitably heavier, and they create more drag. From the start designers had to negotiate toward a weight-to-area balance that had never existed.

Engineers obsessively modeled and counted every kilogram, cut wherever they could. Obviously dense parts of the system, such as the batteries that would power the plane's propellers and computers, were intensely scrutinized. So was every other part, down to the toilet seat.

"Ideally you would choose the pilot based on weight, too," said Peter Frei, one of the lead designers on the project and a former fighter pilot who served with Borschberg. "And you would have a 40-kilogram [88-pound] woman flying this plane." He shrugged. "But we have the guys we have."

Currently the Solar Impulse 2 weighs about 5,071 pounds (2,300 kilograms), similar to some large SUVs. Hardly weightless, though still very good, Borschberg said, considering the second important design variable: surface area.

Not long after Solar Impulse was founded in 2003, Borschberg and Frei flew to California to meet with the legendary MacCready. He died in 2007, long before the first Solar Impulse prototype flew, but Borschberg remembers he had said: "Make the wings big." And so they now are—slightly longer than those of a Boeing 747-8 Intercontinental, an airliner that seats more than 460 passengers.

All of this surface area—and more along the stabilizers and spine of the craft—is given over to 17,248 solar cells made of monocrystalline silicon, each as thick as a human hair. They're less efficient than top-of-the-line cells used in satellites, but, crucially, they're less expensive and lighter. Together the cells, batteries, wings, and onboard computers embody what Borschberg said was the best possible outcome of an engineering tug-of-war. At one point he told me the project was not so much about adventure, or even flight, as it was about energy management. He admitted that didn't sound sexy.

View Images To power the plane, more than 17,000 photovoltaic cells, each about as thick as a human hair, line the wings, fuselage, and stabilizers. The cells generate enough power for the plane's four electric motors—but that still isn't much. During flight, the plane's average speed will be about 43 miles (69 kilometers) per hour. Photograph by Jean Revillard, Solar Impulse

Still, all of this goes only so far. The Solar Impulse 2 is efficient, but so light that it must avoid even moderate winds that other planes could plow through head on. And it's not powerful—the solar cells provide only about 20 horsepower apiece to its four engines. One way to think of it is to imagine the plane rolling down the runway at dawn, all grace and Swiss precision, with two lawnmowers strapped to each wing. The Solar Impulse 2 may be an inspirational concept, but the 747 still wins with the vacation crowd.

Piccard was careful to draw a distinction between his plane and commercial aviation.

He and Borschberg hope the project and its technology will lead to more innovation—perhaps in drones or in satellites that fly within the Earth's atmosphere rather than outside it, in space. Borschberg said the project was like a startup that had routed everything into its initial public offering (IPO). Piccard told me, with his characteristic expansiveness, that he wasn't sure where it would lead.

"If you take the electricity generated by our plane and put it into a modern airliner, it barely powers the entertainment system," he said. "But that is not our goal. We are explorers first."

View Images Solar-powered aircraft are, by necessity, lightweight, which means engineers try to carve away every unnecessary ounce of equipment. This attention to weight-saving led the designers to build a tight, one-person cockpit with a seat that doubles as a toilet and also reclines so the pilot can rest. Photograph by Jean Revillard, Solar Impulse

Let others wrestle the dream down into a doorbell.

"Therapy for the Planet"

Designing the Solar Impulse aircraft was one thing. Finding materials to build it was another. After Borschberg completed his feasibility study and joined Piccard, he ran into supply problems straightaway. Piccard's vision had been deemed possible, and this made it seductive but by no means assured. While the individual technologies used in the plane already existed, most of them weren't refined enough to stand up to the challenge. This is partly why it's taken more than a decade for the project to mature.

"The aviation world did not have the technology to build this," Borschberg said. "So we had to bring all of these things together to do it. We stretched the technology to the edge, and then we tried to find companies that would work with us."

Few of them turned out to be directly involved in aviation. Among more than a hundred sponsors and suppliers that have backed the project, only one, the French firm Dassault, builds planes.

During 12 years of testing and searching, more improvements became possible. Battery storage capability, long a hindrance to the evolution of electric vehicles, significantly improved. So did photovoltaics, engine efficiency, and the carbon-fiber nanotechnology that keeps the plane light but strong, so it's less likely to crack under stress.

Even awareness of clean alternatives to fossil fuel energy production has boomed, particularly in developing nations, a trend Piccard plans to tap as the plane circles the globe. (He calls such clean technologies "therapy for the planet.")

The other reason for the long incubation period was money. Piccard and Borschberg said they began with none. At the time of their first meeting, Borschberg was an entrepreneur in the field of semiconductors; Piccard was still managing a private psychiatry practice. Both would soon drop most of their work to focus full-time on promoting the project.

View Images In April 2014 the Solar Impulse 2 was rolled out of its hangar in Payerne for tests of its solar array. Several solar aircraft have been built and flown successfully, including manned and unmanned models—some of them massive—but none has ever been flown for days at a time, through nights and across oceans. Photograph by Jean Revillard, Solar Impulse

"The first thing we did was announce our plans," Piccard said. "We didn't have money, no sponsors. We immediately burned all the bridges behind us. It's a great motivator. When no one knows what you're doing, it's a lot easier to quit."

Borschberg said the project has so far cost 150 million Swiss francs ($160 million U.S.), all of it privately raised. This isn't a lot in the world of big aviation (a single Boeing 747-8, for example, costs about $368 million), but Piccard said there had been several moments when he worried they would run out of cash.

The latest of these came in 2013, after a test flight across the United States with the Solar Impulse 1, the group's prototype. At the time, the project was two months shy of stalling out, according to Piccard. Then Google co-founder Larry Page stepped in, apparently impressed with the success of the cross-country flight. Other supporters followed. Now Google's name can be seen on the plane's forehead, just above the windscreen.

A crew member said, "Oui. Of course we weighed the letters."

Into the Unknown

In late February, the cavernous hangar in Abu Dhabi where Piccard and Borschberg had set up their headquarters hummed with activity. Sixty or so crew members, including engineers and logistics personnel, a yoga teacher, and a team of chefs, ranged through the space. At long, white tables, media relations staff and personal assistants tapped at laptops, while elsewhere Swiss civil aviation authorities inspected late adjustments to the cockpit of the Solar Impulse 2.

The atmosphere was high-spirited, occasionally tense, and very busy—somewhere between the heavy thrum of a military command center and the buzz of a tech company. Piccardian phrases like "mission-oriented" and "pioneering spirit" were often spoken, in English and also French and German, as most of the team is Swiss.

Bad weather had spun in, bringing stiff gusts and dust-filled skies, the sun an indistinct flare wandering above the desert. Not the sorts of conditions that usually ground jet aircraft, but for solar-powered planes, niche creatures as a rule, they pose serious problems.

Already a shakedown flight had been postponed, and the original liftoff date of March 1, which happened to be Piccard's 57th birthday, had to be pushed off by a week. The crew mostly took it in stride, though a sense of expectation was building. Some of them had poured a decade into the project, planning every detail, wrestling through every decision. Monsoon season would soon arrive. If liftoff were delayed, fierce winds over the Pacific could ground the plane for at least a year. Maybe longer.

For his part, Borschberg, usually obsessed with details, did not seem concerned.

View Images In August 1960, Bertrand Piccard's father, Jacques, and Don Walsh became the first humans ever to reach the bottom of the Pacific Ocean's Mariana Trench, the deepest known spot on Earth. The men spent five hours sinking seven miles (11 kilometers) to the seafloor aboard the Trieste, which Jacques Piccard had designed with his father, Auguste. Photograph by Thomas J. Abercrombie, National Geographic

"We've spent a long time worrying, eh?" he said, grinning. "The danger now is in what we didn't prepare for."

Weather is the most unpredictable and dangerous variable of all, but in some ways it's the easiest to dismiss—at a certain point, there's nothing you can do about it. Borschberg was thinking ahead, to the great reaches of ocean.

The Solar Impulse 2 can fly through rain, and its solar cells harvest power even on cloudy days. During the voyage, a mission control team headquartered in Monaco will track the plane and provide the pilot with weather forecasts and options for avoiding turbulence and storms. They have chosen the plane's path carefully, planning the route for maximum summer sunshine, short nights, and shiny, happy weather.

But still, that blank blue empire.

During the three maritime legs, the pilots will enter territories of desolation, without runways, where countless explorers before them, including the aviator Amelia Earhart, vanished. No support plane will trail them, no boat sail below. In case of ocean crashes or bailout, rescue could take hours, or days. The case of Malaysia Airlines Flight 370, which was carrying 239 passengers on a routine commuter route when it disappeared one year ago over the Gulf of Thailand, illustrates the disaster that can befall even large aircraft, flying in good conditions. Everyone in the hangar knew the stories, had heard Borschberg and Piccard answer questions many times about fear and risk. There was little left to say.

A Point Beyond Fear

View Images To prepare for long flights over vast reaches of ocean, Piccard and Borschberg spent days at a time training in a flight simulator. During their flights they will periodically rest in 20-minute increments while an autopilot computer handles the flying. Photograph by Fred Merz, Solar Impulse

In 1999, while crossing the Pacific during his round-the-world balloon flight, Piccard lost contact with his mission controllers for 48 hours. Winds that had carried them swiftly along suddenly disappeared. They drifted for days, never completely still, though it felt like stillness, like loss. Piccard and his co-pilot grew anxious. Then frightened. To be alone above all that water. No voices but their own. Possibly Earhart had known this sensation, too, before the end. Piccard wrote of the passage later, describing the ocean as "a mirror in front of which it is impossible to fool myself."

Earlier he had passed over the Mariana Trench, the greatest of abysses, into which his father had descended in 1960 aboard a submersible named Trieste. Jacques Piccard and American Don Walsh spent five hours sinking to the bottom. They heard cracks on the way down, and felt a jolt—a Plexiglas window cracking somewhere in the sub—but it did not deter them. They set down into "snuff-colored ooze" and peered through the sub's tiny windows at the black, crushing void. In all they spent 20 minutes at the deepest place men had ever reached. Then they retreated into the light.

I asked Piccard if he had ever thought to follow his father down into the sea. So much of it remains unknown, so much unreached. Irresistible, I thought, for explorers. But Piccard's days before the mirror had left him certain.

"No," he said, immediately. "It's always been the sky for me."

Important, then, to consider the sky's perils. Among them lightning, hail, birds. Boredom. The men will have to stay alert for hours, days, in the plane's tight cockpit. There would also be high-altitude cold, and the possibility of altitude sickness, as experienced by climbers on Mount Everest.

Most of these problems were addressed technically: hours of training in flight simulators, for example, and layers of insulating foam to cocoon the cockpit. There is also oxygen in bottles for breathing, energy drinks and protein bars for eating, cozy-looking black UGG boots for the pilots' feet, and, in case of ditching, a parachute and a life raft. There is, too, the reclining seat. Upon this Piccard and Borschberg plan to take periodic naps of no longer than 20 minutes, leaving the flying to an autopilot.

View Images Borschberg exercises during a 72-hour flight simulation test in 2012. Yoga and meditation techniques, as well as self-hypnosis, will be employed during flight to help the pilots remain mentally and physically well. Their vital signs will also be monitored from a mission control center in Monaco. "Hypnosis is simply another kind of exploration," Piccard says. "Spiritual exploration." Photograph by Jean Revillard, Solar Impulse

Finally, though, there is the mind, which defies engineered solutions. Mission control will monitor their vital signs remotely, but each man has drawn up a regimen to help him rest, focus, and remain mentally well during the days and nights aloft. Both will employ yoga techniques on the reclining seat, developed with the help of Borschberg's personal instructor, Sanjeev Bhanot. Without a demonstration I was never sure how, as with various toilet scenarios, the yoga would really work out, though Bhanot told me, "All that's required for awareness is space and time. They will have plenty of that."

Piccard will also seek replenishment through his long-prescribed method of self-hypnosis.

"Hypnosis is a simply another kind of exploration, spiritual exploration," he said. "All of this—the flight, the clean energy, hypnosis, meditation-it's all about learning and trying to improve life on this planet."

I lost him, briefly, during the part about cockpit transcendence. In boyhood I had read the classic tales of Ernest Shackleton, Antoine de Saint-Exupéry, John Wesley Powell, T. E. Lawrence, and more recently Earhart and Gertrude Bell. It was difficult to imagine any of them kicking back into down dog during their explorations (to be clear, Borschberg said that position would not be possible). Shackleton was too busy holding off hypothermia. The aviator Saint-Exupéry, though a poet, was often occupied with crashing or trying not to crash in the days before autopilot. As for Earhart—who knows? Of them all she may have have been most open to Piccard's brand of wonder.

Piccard's grandfather, Auguste, had known Earhart. Piccard grew up with her name in his ears, along with the voices of those many other explorers. Some of them lived through their adventures; some did not. Now Piccard and Borschberg will aim a solar ship toward a point between their myths and deeds, hoping to inspire the planet. Who is to say what course they should set, which techniques or philosophies to trust? They have come this far. They have prepared all there is to prepare. Now wind, water, and light await.

View Images On a recent test flight, the Solar Impulse 2 soared above the Sheikh Zayed Grand Mosque in Abu Dhabi. Weather permitting, the plane will launch in the coming days, heading westward to India on the first leg of its round-the-world voyage. Photograph by Jean Revillard, Solar Impulse