The Solar Impulse project began in Switzerland in 2003, when Bertrand Piccard—a veteran balloonist and also a psychiatrist—began designing and building a one-man airplane that could fly without fossil fuels, using only the sun’s energy. After five years of development, Piccard joined forces with Swiss pilot and businessman André Borschberg to finish the aircraft and help organize the project to circumnavigate the globe in their experimental solar-powered plane. The first version of the plane, Solar Impulse 1, became the first solar-powered aircraft to fly for 26 consecutive hours, as well as the first to cross two continents. Solar Impulse 2 would blow those records out of the water, if not out of this world.
Leg 1: The adventure begins in Abu Dhabi
The experimental aircraft began its round-the-world solar-powered journey on March 9, 2015 lifting off from Abu Dhabi in the United Arab Emirates. From there, Borschberg piloted Solar Impulse 2 in the early morning hours for what would be a relatively short flight in comparison to other legs of the journey. He flew 13 hours and 1 minute before touching down in Muscat, Oman for the first scheduled stop of the journey that would ultimately take more than a year to complete.
Related: Zero fuel Solar Impulse 2 takes off on world’s first round-the-world flight powered entirely by sunlight
Leg 3: Longest solar-powered flight in aviation history
The 15-hour, 20-minute flight from Oman to Ahmedabad, India on March 18, 2015 marked the first of many world records on the Solar Impulse journey. With Piccard in the cockpit, the experimental aircraft flew longer than any other solar-powered plane had before that date. This set an exciting precedent for the project early in the RTW adventure, as the SI2 would beat its own record several times over before landing back at its starting point more than a year later.
Leg 7: Unscheduled landing in Japan
After multiple weather-related delays, SI2 took off from Nanjing, China on May 31, 2015 with Borschberg in the cramped cockpit and headed east toward Hawaii. However, it soon became apparent that the chosen route for the longest leg of the round-the-world trip was not meant to be. The poor weather forecast forced the ground team to scramble to make arrangements for Borschberg to detour the aircraft for an unscheduled landing in Nagoya, Japan. The plane was grounded for several weeks while the crews waited for the weather forecast to improve. Solar Impulse 2 was finally cleared for take off again on June 28.
Related: Solar Impulse could be grounded for a whole year in Japan
Leg 8: Pacific Ocean crossing
The longest leg of the round-the-world journey also marked two of the most significant world records for the project: the longest continuous flight by a solar-powered aircraft as well as the longest solo flight in aviation history. Borschberg piloted the SI2 on the 117-hour, 52-minute flight, covering the 4,819 nautical miles between Nagoya, Japan and Oahu, Hawaii. To endure such a long flight in a cramped cockpit, the pilot employed yoga and meditation techniques to encourage circulation in his extremities. After the first 24 hours of the flight, he was also able to take 20-minute catnaps while the plane’s autopilot system kept it on course. As Borschberg landed in the plane in Hawaii on July 3, 2015, thousands of viewers around the world watched the live streaming webcast on the Solar Impulse website.
Leg 9: Grounded in Hawaii
Although the record-setting longest flight went smoothly, the SI2 had to be grounded after landing in Hawaii due to an overheated battery. As experimental aircraft go, SI2 encountered relatively few technical difficulties along its journey, but this one was a show-stopper. Once ground crews examined the battery, it was determined that the best course of action for the project was to put the journey on hold until replacement batteries could be produced and tested to ensure subsequent flights would be safe. Testing on the new batteries began in early February 2016, and the plane was finally cleared for takeoff in April, and Piccard flew the airplane to California without further incident.
Leg 14: SI2’s shortest flight
Lasting a mere four hours and 41 minutes, the 14th leg of the solar-powered flight was the shortest by far. After making several stops in its eastbound journey across the continental United States, Solar Impulse 2 took off from Lehigh Valley, Pennsylvania on June 11 and touched down just a few hours later at its final U.S. destination: New York City’s JFK Airport. A remarkable milestone, SI2 flew over the Statue of Liberty during its approach to the airport, creating an iconic image that represents the ability of clean energy to grant freedom from dirty fossil fuels.
Leg 15: Crossing the Atlantic Ocean
Flying a 100-percent solar-powered airplane across the Atlantic Ocean was perhaps an easier feat than the Pacific crossing, but secured Solar Impulse 2 yet another world first record. Piccard took off in the early morning hours of June 20—the longest day of the year—from NYC’s JFK airport and successfully flew for 71 hours and eight minutes, landing in Seville, Spain on June 23.
Leg 17: Back to Abu Dhabi
When Piccard landed SI2 in Abu Dhabi on July 26, a few things happened. First and foremost, the team nabbed a major victory in achieving the goal of flying a solar-powered airplane around the world. Secondly, Solar Impulse 2 secured an esteemed place in clean energy history, proving the awesome potential of solar power and, with any luck, inspiring engineers around the world to discover new innovations in renewable energy applications.
The final leg of SI2’s circumnavigation was a tricky one, occurring during one of the most intense heat waves the world has seen in recent decades. Weather patterns forced Piccard to fly in a holding pattern soon after take off, lengthening the expected 40-hour flight to a final duration of 48 hours and 37 minutes. Although the journey’s last leg was one of the shorter flights, the obstacles only served to enhance the anticipation as the solar-powered electric airplane zeroed in on its ultimate goal: a 26,744-mile trip around the world without fossil fuels.
This won’t be the last we hear from Piccard, Borschberg, and the rest of the Solar Impulse support team. A plan has already been discussed to use SI2’s proven technology to create solar-powered drones, and nobody would be surprised if a Solar Impulse 3 were to emerge in the coming years as a bigger, better version of the sun-powered airplane. For now, the pilots will celebrate this enormous victory for clean energy, and perhaps take a little time off after spending so many hours in the SI2’s cramped cockpit.
+ Solar Impulse
Lead image via Abu Dhabi Government, all other images via Solar Impulse