Solar Impulse 2 — the giant, gangly solar-powered aircraft on a protracted, multi-leg trip around the world — just completed its single most challenging task: a record-breaking leg from Nagoya, Japan to Hawaii lasting 4 days, 21 hours and 51 minutes, making it the longest-duration solo flight in history. The flight was handled by André Borschberg, who has been piloting the craft on alternating stints with project co-founder Bertrand Piccard. (The Verge spoke with both pilots about the harrowing journey several weeks ago.)

Borschberg was originally planning to fly from Nanjing, China to Hawaii in one continuous journey, but deteriorating weather conditions forced him to cut the leg short with a layover in Japan. The aircraft, which must fly high during the day and low at night to carefully manage solar charging and discharging of its batteries, cruises at a very low speed and relies on nearly perfect weather to fly safely; in high headwinds, the plane's groundspeed can actually be negative.

Piccard and Borschberg are using the Solar Impulse 2 as a tool to raise awareness about the benefits of renewable energy, but the tour doesn't stop here: the aircraft will fly next to the contiguous United States, before eventually returning to Abu Dhabi where the round-the-world journey began in early March. The timeline to finish is flexible depending on weather conditions, however — the crew waited for weeks in Japan before taking off for Hawaii.