Solar Impulse 2 passes halfway point in trans-Pacific flight

The aircraft, which began its round-the-world journey in Abu Dhabi in March, had travelled 55 per cent of the way to Hawaii by 10am UAE time, having flown 4,305 kilometres, with 3,430 kilometres more to go.

Pilot Andre Borschberg flying the Solar Impulse 2 which has just passed the halfway point of its Pacific Ocean crossing. Courtesy Solar Impulse

TOKYO // Solar Impulse 2, the aircraft flying between Japan and Hawaii as part of a round-the-world attempt at solar flight, passed the halfway point of the perilous Pacific Ocean crossing yesterday, breaking its own endurance record in the process.

The aircraft, which began its journey in Abu Dhabi in March, had travelled 55 per cent of the way to Hawaii by 10am UAE time, having flown 4,305 kilometres, with 3,430 kilometres more to go.

By that time the plane and its veteran Swiss pilot Andre Borschberg had logged 61 hours of continuous flight – easily bettering the previous record of 44 hours they had set between China and Japan.

“Already halfway through what is probably the flight of my life! Loving it!” Mr Borschberg tweeted from the cockpit.

On the third day into the eighth leg of the global circumnavigation, expected to take five days and five nights and billed as the most difficult part of the adventure, the plane crossed a potentially problematic cold front, the project said.

That front – which stretches across the Pacific – is one of the factors that had kept the team stranded in Japan for almost the entire month of June.

“#Si2 crossed the 1st cold front, major hurdle overcome,” the team tweeted.

The experimental solar-powered aircraft left Japan about 9pm UAE time on Sunday, after spending a month in Nagoya in central Japan.

The propeller-driven plane was scheduled to fly directly from Nanjing in China to Hawaii, but bad weather along the way forced a diversion to Japan that stretched to a month.

Mr Borschberg is entirely self-reliant in the 3.8-cubic metre unpressurised cockpit.

Travelling at altitudes of more than 9,000 metres, he has to use oxygen tanks to breathe, and experiences huge swings in temperature throughout the day.

He rests for only 20 minutes at a time and cannot move from his seat, which has a built-in toilet, as well as a parachute and a life raft attached.

Sleeping, however, has always been the issue for Solar Impulse. On day two of his journey, Mr Borschberg was allowed only one 20-minute resting period for the entire day as technical limitations and flight controls demanded that he be awake for the rest of the journey.

“This is not much, so he has to be really focused on his different tasks on the plane even with a few days with very short sleep,” said Dr Raphael Heinzer, a sleep specialist at Centre Hospitalier Universitaire Vaudois, in a video on the project’s website.

Over the next two days, Mr Borschberg will probably get only six resting windows. Added up, this amounts to two or three hours of sleep a day, or about 15 hours for the entire trip.

Typically, the human body begins to suffer after 24 hours of sleep deprivation. A University of California, San Diego study shows that sleepier subjects displayed more activity in the prefrontal cortex, or an area of the brain responsible for memory and reasoning. This was interpreted to show that the sleepier the person was, the harder it was to do simple tasks, let alone fly a fuelless plane.

Solar Impulse 2's mission is to circumnavigate the globe without using a single drop of fuel. It has 17,000 solar cells and on-board rechargeable lithium batteries, allowing it to fly through the night. Its wingspan is longer than a jumbo jet's but it has the weight of a car – only 2.3 tonnes.

* Agence France-Presse with additional reporting by Naser Al Wasmi