UPDATE: May 31, 9:47 a.m. ET

Solar Impulse is currently flying near Japan as part of its six-day Pacific Ocean leg. The plane is relying on its batteries for power, as it looks to circle the globe while running only on sunlight.

A week ago, André Borschberg had a bad gut feeling about piloting the toughest leg of the first around-the-world flight powered only by the sun. But before lifting off in China early Sunday morning local time, his ominous emotions transformed into excitement.

Noting that the confidence of the team behind the Solar Impulse flight was palpable, Borschberg said he felt excited about what has been dubbed the "moment of truth," the approximately 8,172-kilometer, or 5,078-mile, oceanic flight to Hawaii.

If successful, the flight will become an aviation milestone.

"I have a great feeling today, completely different than a week ago," Borschberg told members of the press before wheels up in Nanjing, China.

But the 130-hour flight in the single-seater aircraft won't be a breeze. It is expected to be difficult, not only because of weather, but also living conditions. Borschberg will have to adapt to extreme circumstances, including living in a small, 3.8 cubic-meter, or roughly 134 cubic-foot, cockpit during the non-stop flight. At night, he can switch to autopilot to sleep for 20 minutes at a time.

I feel confident about this flight from Nanjing to Hawaii. It will be the flight of my life pic.twitter.com/PacWPjEvDD — André Borschberg (@andreborschberg) May 30, 2015

For the #solar flight across the #Pacific, I will take with me 2.5 kilos of food and 3.5 liters of water per day pic.twitter.com/45mQLTSKGh — André Borschberg (@andreborschberg) May 4, 2015

For the #Pacific, I need to be ready for the unknown: I’m not sure how #Si2 will behave over so many days and nights pic.twitter.com/I31FHaQTmh — André Borschberg (@andreborschberg) May 30, 2015

The China to Hawaii leg is the seventh and longest one of the around-the-world trip, which began in March with a flight from the United Arab Emirates to Oman. Once Solar Impulse 2 reaches Hawaii, it will continue on to Phoenix, Arizona.

Borschberg will be aided by Bertrand Piccard, Solar Impulse's chairman. Piccard is also a pilot and world-record holder for his long duration balloon flights.

“This is the exploration leg of the flight around the world," Piccard said in a statement. "It will be an important milestone for aviation with an airplane capable for the first time ever to fly with unlimited endurance."

The goal of the around-the-world flight is to prove that the impossible is achievable, according to a statement from Solar Impulse.

Nine hours into the flight, Solar Impulse 2 entered South Korean air space. The plane's batteries were being powered by the sun throughout the flight and by 11:55 a.m. China time, they were almost fully charged.

.@andreborschberg is entering the South-Korean airspace after almost 9 hours of flight! #futureisclean pic.twitter.com/bncRi07US8 — SOLAR IMPULSE (@solarimpulse) May 31, 2015

Amazing view of @andreborschberg flying above the sea, who did a U-Turn to avoid cirrus clouds http://t.co/JIj9tHK6hl pic.twitter.com/rhiCId5vVV — SOLAR IMPULSE (@solarimpulse) May 31, 2015

Borschberg listened to music while flying and also sent out a tweet praising Solar Impulse's Mission Control Center in Monaco.

Without the Mission Control Center, I would be blind. They see ahead of me, in the future #Pacific pic.twitter.com/CeTTrw3Re9 — André Borschberg (@andreborschberg) May 31, 2015

You can track the flight, live at www.solarimpulse.com.

UPDATED May 31, 4:34 p.m. China time: with more information about ongoing oceanic flight, including its entry into South Korean airspace.