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Solar Impulse takeoff
Solar Impulse CEO Andre Borschberg flashes a thumbs-up as the Solar Impulse 2 airplane, piloted by Bertrand Piccard, rises from its runway in Hawaii. (Credit: Solar Impulse)

More than a year after its odyssey began, the Solar Impulse 2 airplane resumed its round-the-world, solar-powered trip in Hawaii today.

The ultra-lightweight plane took off at 6:18 a.m. Hawaii time (9:18 a.m. PT).

Solar Impulse began the trek in March 2015, taking off from Abu Dhabi and making stopovers in Oman, India, Myanmar, China and Japan. It got as far as Hawaii last July.

That five-day, five-night nonstop flight across the Pacific to Hawaii took a heavy toll on the plane’s batteries. The system overheated, and it took several months to make the repairs. The team also had to wait for reliably good weather to return.

Now the $150 million project has gotten off the ground again.

“OK, let’s go!” Solar Impulse chairman and pilot Bertrand Piccard radioed from the single-seat cockpit. Moments later, the plane gently rose into a partly cloudy sky.

“Have a great flight, Bertrand,” Andre Borschberg, Solar Impulse’s CEO and alternate pilot, said from the runway at Kalaeloa Airport. “Enjoy it, and don’t forget to come down!”

Piccard is expected to make the flight to Moffett Airfield in Mountain View, Calif., over the course of 62 hours. It’s the first leg of a renewed campaign that’s due to cross North America and the Atlantic, then head through Europe and end up where the odyssey started, in Abu Dhabi.

The point of the 22,000-mile flight is to demonstrate environmentally friendly technologies. Solar Impulse 2 is an upgraded version of the solar-powered plane that made a two-month-long journey across America in 2013.

More than 17,000 solar cells cover the plane’s wings, fuselage and tail, feeding 1,400 pounds of lithium polymer batteries. Four 17-horsepower electric motors, each packing the power of a small motorbike, push the plane through the air. The system is designed to fly through the night, relying on stored energy.

Thanks to advanced carbon composites and insulation, Solar Impulse 2 has a wingspan wider than a Boeing 747 jet (236 feet) but weighs only about as much as a family car (5,100 pounds).

The downside is that its travel speed is also in the family-car range: a maximum of about 87 mph, and an average of 40 mph or so. That’s why it’ll take two and a half days of nonstop flying to make the 2,400-mile trip to Moffett Airfield. During that time, Piccard will have to pilot the plane, eat, drink, sleep and do whatever else needs to be done in a seat that can convert into a couch as well as a toilet.

Piccard and Borschberg will take turns in the cockpit for what’s expected to be at least five marathon flights. In between, there’ll be stopovers to recharge the batteries – and recharge the flight team as well.

You can follow the flight via Solar Impulse’s website, YouTube channel and Twitter account (@solarimpulse).

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