Updated: October 8, 2015 11:35 AM ET | Originally published: August 20, 2015 10:34 AM EDT

Bertrand Piccard and Andre Borschberg are on a mission to make history. To prove a point about the power of clean technologies and renewable energy sources, they are piloting the Solar Impulse 2 plane around the world using absolutely no fuel.

The plane, which is powered by the sun, weighs 5,071 lbs. (2,300 kg) and has a solar panel-covered wingspan of 236 ft. (72 m). Solar Impulse 2 set the record for the world’s longest solo flight at 4 days, 21 hours, and 52 minutes earlier this year while traveling from Japan to Hawaii.

Piccard and Borschberg started their journey in March and hope to finish by summer 2016. The plane is currently grounded through the winter to repair the batteries, but for the two pilots, the journey isn’t about how long it takes to cross the finish line. According to Piccard, “It’s not a race against time. It’s an attempt at making a historic first so the time it takes finally is not so important. What we need is to get back to the place where it started.”

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Write to Julia Lull at julia.lull@time.com.

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