Solar Impulse 2 sets off on Pacific crossing from Japan to Hawaii, expected to last five days and nights in most difficult leg yet of Andre Borschberg’s attempt

A solar plane took off for what could be the longest solo flight in history on Monday, with its Swiss pilot confronting the “moment of truth” of a journey around the Pacific Ocean and around the world.



The Solar Impulse 2 set off about 3am from Nagoya, Japan, en route to Hawaii, a trip expected to take five days and nights of continuous flight.

The Pacific crossing represents the most difficult leg of Andre Borschberg’s attempt to circumnavigate the world in a multi-stage flight.

Borschberg was delayed in Nagoya for weeks after “a wall” of bad weather forced an unplanned landing and his original flight, from Nanjing, China, was diverted in early June to Japan.

The Swiss pilot flew for 44 hours from Nanjing to Nagoya – two days and two nights – and rested only in 20 minute intervals. To cross the Pacific he will have to repeat the feat two and a half times over.

Solar aircraft to be flown across the Pacific in world record bid Read more

“We really are in the moment of truth now,” Conor Lennon, a member of the Solar Impulse team said from the project’s headquarters. “It’s the moment of truth technically and in human terms as well. Can the plane manage it?”

“There’s a lot of uncertainty at the end, we cannot know everything,” Bertrand Piccard, Borschberg’s project co-founder and occasional co-pilot, said after the team decided to fly. “Today we accepted the decision to go, we accepted that risk, we believe the window is good.”

Piccard said that the window to reach Hawaii is “a little bit tight” and that “maybe we’ll be a little bit late” before a weather system moves into the plane’s path. The plane’s crew has spent weeks trying to gauge long-range weather forecasts to find a window for the crossing.

With wind and turbulence calmer in the predawn hours of the morning, the Solar Impulse 2 took off in the darkness equipped with full batteries that would recharge as the sun rises over the ocean. The plane has 17,000 solar cells on its wings and a top speed of about 87mph, faster than a ship but much slower than traditional aircraft.

Designed to be lightweight – its carbon-fiber build and lithium batteries weigh little more than two tons, about as much as a car – the plane is threatened by strong winds and bad weather like the driving rains that halted its progress for weeks in Japan.

Borschberg’s home for the next five days will be a 130-cubic-foot cockpit, in which he’ll have to keep the plane gliding as much as possible during the day to save power, guiding it into patches of sunlight and using its motors as little as possible.

He will also have to endure altitudes of 28,000ft and temperatures close to 100F (37C) in the unpressurized and unheated cockpit. Meanwhile the entire Solar Impulse team will help recalculate the plane’s journey every day, adjusting for weather and other variables that might affect its trajectory.

“We are really at the limit of what the technology can provide,” he told the Guardian last month.



“The step we make forward is huge,” he said. “We didn’t have the chance to test this airplane day and night, we never flew over the oceans. There is no way to go back, so when you leave the coast of China you are committed to go to Hawaii, you are committed to fly five days five nights. You have to go to the end.”

Borschberg, a 62-year-old Swiss engineer, performs yoga to help stay alert and rested during flights.

The plane began its circumnavigation from Abu Dhabi in March, stopping in Muscat, Ahmedabad, Varanasi, Mandalay, Chongqing and Nanjing – and breaking records for solar flight along the way.

In May, Piccard compared his and Borschberg’s challenge with achievements on par with those of other aviation pioneers.



“Eighty years ago, maybe we would have done like some of the pioneers, like Amelia Earhart,” Piccard said. “That means taking off without knowing what would happen and disappear.”

Earhart vanished over the Pacific in 1937 attempting the hazardous crossing over 5,000 miles of ocean, through unpredictable weather and long hours of exhausting work. In June a team of researchers has traveled to the tiny atoll of Nikumaroro in the south Pacific, where they believe her plane crashed and wreckage remains to this day.

Solar Impulse would be more cautious than its predecessors, Piccard said: “We don’t want to be daredevils. It would be stupid. We have the tools to make it in a safer way.”

If successful, Borschberg will have beaten the the standing endurance record for solo flight in any plane by about two days.

On Tuesday Piccard admitted that doubts sometimes creep into his mind about safety, but expressed confidence about the mission.

“You create your own very dark scenarios,” he said. “What happen if all the engines fail and the plane is in the water – OK – and then you go back to the reasonable decision-making. We have a narrow plane we have tested, it works, it’s fine. We have a good team, we have people ready to make it happen.”

Borschberg has also dismissed risks, and said that he has faith in his training and emergency equipment: a parachute and life raft for worst-case scenarios.

After landing Hawaii, Borschberg plans to fly to Phoenix, Arizona, for another leg of the journey of comparable length to the first flight over the Pacific.

The original Solar Impulse flew a 26-hour flight in 2010, proving that a solar-powered aircraft could store enough energy in its lithium batteries to keep flying at night. The Swiss engineers hope that their innovations with solar power and energy efficiency can be incorporated into other technologies and daily use around the world.