Solar Impulse 2 to resume solar-powered flight around the globe

Solar Impulse 2, the solar-powered plane seeking to circle the globe, is expected to take to the skies again this coming week, having been grounded for nine months.

The aircraft shattered the record for a non-stop solo flight, with pilot André Borschberg staying aloft for five days and five nights as he traversed the Pacific Ocean between Japan and Hawaii, but in the process about half the battery cells overheated.

The forced interruption proved invaluable, both for the aircraft, which received some much-needed attention, and for the team’s dynamics, which had suffered under some major disagreements between cockpit and ground staff.

“The past eight months have exemplified the team spirit, embracing setbacks and seeing them as opportunities,” write the Solar Impulse team on their blog. “After replacing the batteries that overheated during the flight from Nagoya to Hawaii, the countdown has now started for the Solar Impulse team to finish what they started, and head back to their departure point: Abu Dhabi.”

So the odyssey began in March 2015, with the 5,000 pound craft lifting its enormous wingspan – equivalent to that of a jumbo jet – from the sands of the United Arab Emirates, for its first short leg to neighboring Oman.

The purpose of the historic effort, as explained on the Solar Impulse website, is “to achieve something that still seems impossible today: the first round-the-world solar flight, powered only by the sun, with no fuel or polluting emissions.”

Clean technology is at the very core of the team’s ethos, with 17,000 solar panels blanketing the wings, providing power for the plane to climb to 28,000 feet each day, then drifting down to 5,000 feet during the hours of darkness, when the sun’s energy is unavailable.

"Before the flight from Japan there was still a very big question mark," Mr. Borschberg told the BBC. “Would we be able to do it? Would the airplane be capable? Would we have enough performance? And of course this is now done; it has been demonstrated, and we go to the next leg with a high level of confidence.”

But the batteries were not the only thing to be strained to the limit during that record-breaking journey. A critical back-up system, which provided something akin to an automated co-pilot, failed, leading many of the ground team to call for the flight to be abandoned.

When Borschberg refused, adamant the conditions were right and he could make the crossing, several engineers threatened to resign.

The plane and its pilot managed to limp to Hawaii, and Solar Impulse flight director Raymond Clerc called in a friend of his - a captain with EasyJet - to help rebuild confidence within the team.

While those relationships were healing, perhaps even growing stronger, the airplane itself underwent modifications, too, not least new batteries and a bolstered cooling system to prevent a repeat of last year’s mishap.

And now all that’s needed is a window in the weather, to fly on to the US West Coast, then to New York, an Atlantic crossing and, finally, back to where it all began in Abu Dhabi.

“It is only a few hours before the flight that we can fully confirm it will take place,” reads the team’s latest blog post. “This state of unknown lasts until the aircraft has taken off and reached the point of no return and is what ultimately motivates all Solar Impulse members, enabling us to become closer than a team: a family.”