Solar plane makes second attempt at longest leg of journey

The Solar Impulse 2 (Si2) solar-powered aircraft embarked at the weekend on the longest leg of its round-the-world attempt, taking off from Japan for the second time after being forced to turn back earlier this month due to poor weather conditions.

The aircraft – which is fitted with more than 17,000 solar cells along its wingspan and fuselage – took off from Nagoya Airfield in Japan late on Sunday, and has already "passed the point of no return", meaning should weather conditions worsen the pilot, Andre Borschberg, no longer has the option of turning around and returning to Japan.

The Si2 plane first attempted the Pacific crossing on June 1, but was quickly forced to retreat to the safety of Japan’s shore as the weather up ahead turned treacherous. Having waited all month for a clear weather window (Borschberg said last week that the mission was in danger of being delayed for a year if weather conditions did not improve), the team was given the all-clear on Sunday and Borschberg is now piloting the aircraft over the ocean in what will become the longest duration solo flight in aviation history should he successfully reach Hawaii in around five days from now.

The Swiss pilot’s ground crew – ably supported by fellow pilot and Solar Impulse co-founder Bertrand Piccard – boasts a large team of meteorologists among its number, and they are confident that a safe weather passage has now been identified to ensure the Si2 arrives safely at its destination.

This, the eighth leg of the journey, has posed the most problems for the aircraft, which is powered 100% by the sun and uses four lithium-ion batteries to deliver power to the plane’s motors during nighttime.

Should the motors fail, Borschberg will be forced to bail out of the aircraft and survive alone in a specially designed dinghy that is packed with enough supplies for several days. The experienced pilot has spent many years preparing physically and mentally for this leg, and has trained his body to sleep in 20-minute spurts, while also using meditation and yoga to stay as alert and as comfortable as possible.