Image copyright Solar impulse Image caption The plane has a bigger wingspan than a jumbo jet but is incredibly light 
 
 A solar-powered plane has passed the "point of no return" in its second bid at making a record-breaking flight across the Pacific Ocean. 
 
 Solar Impulse took off from Japan's Nagoya Airfield at 18:03 GMT on Sunday. 
 
 The journey to Hawaii is expected to take approximately 120 hours. 
 
 The team spent nearly two months waiting for clear weather to cross the Pacific, and a developing cold front forced the plane to make an unscheduled landing in Japan earlier this month. 
 
 "Andre Borschberg has passed the point of no return and must now see this 5 days 5 nights flight through to the end," Solar Impulse said on its website. 
 
 The pilot now no longer has the option to turn around and return to Japan, if the weather forecast changes. 
 
 Weeks of delay 
 
 The first attempt to fly over the ocean was cut short after a change in the forecast forced an unscheduled landing. 
 
 And another attempt to take off last Tuesday was cancelled at the last moment because of concerns about the conditions. 
 
 If the pilot succeeds, it will be the longest-duration solo flight in aviation history, as well as the furthest distance flown by a craft that is powered only by the Sun. 
 
 The Pacific crossing is the eighth leg of Solar Impulse's journey around the world. 
 
 But this stage has proven to be the most difficult, and has been hit by weeks of delays. 
 
 Image copyright Reuters Image caption The plane had to make an unscheduled landing in Japan after its first attempt to cross the ocean 
 
 Swiss pilot and Solar Impulse co-founder Andre Borschberg, who is flying the experimental single-seater craft, was initially supposed to begin his journey to Hawaii from Nanjing in China. 
 
 But he spent weeks there, with his ground-support team, waiting for the right flying conditions to present themselves. 
 
 He finally took off on the 31 May, but a deterioration in the forecast a few hours into the mission meant that he had to divert to Japan. 
 
 The rainy season in Nagoya has meant another long wait there - but after the false start last week, meteorologists are now confident they have found a weather window to make the five-day, five-night crossing to Hawaii. 
 
 A spokesperson said that the plane would be heading straight out across the Pacific. 
 
 LEG 1: 9 March. Abu Dhabi (UAE) to Muscat (Oman) - 772km; in 13 hours and 1 minute 
 
 LEG 2: 10 March. Muscat (Oman) to Ahmedabad (India) - 1,593km; in 15 hours and 20 minutes 
 
 LEG 3: 18 March. Ahmedabad (India) to Varanasi (India) - 1,170km; in 13 hours and 15 minutes 
 
 LEG 4: 18 March. Varanasi (India) to Mandalay (Myanmar) - 1,536km; in 13 hours and 29 minutes 
 
 LEG 5: 29 March. Mandalay (Myanmar) to Chongqing (China) - 1,450km; in 20 hours and 29 minutes 
 
 LEG 6: 21 April. Chongqing (China) to Nanjing (China) - 1,241km; in 17 hours and 22 minutes 
 
 LEG 7: 30 May. Nanjing (China) to Nagoya (Japan) - 2,852km; in 44 hours and 9 minutes 
 
 Leg 8: 28 June. Nagoya (Japan) to Kalaeloa, Hawaii (USA) - 8,000km; 120 hours (estimated) 
 
 The experimental craft - which has 17,000 solar cells - is powered only by the Sun. 
 
 Once over the ocean, if it fails to soak up enough rays to fully charge its batteries and make it through the night, the pilot could be forced to bail out. 
 
 Mr Borschberg has been trained for that eventuality. 
 
 He has a dinghy and enough supplies for several days while he waits for the team to identify a vessel to go pick him up. 
 
 But, of course, the team hopes none of this will be necessary. 
 
 Mr Borschberg's will spend the duration of the flight strapped into his seat in a cockpit that is about the same size as a telephone booth. 
 
 He will only be allowed to take 20-minute cat-naps, but says he will use yoga and meditation to make his journey more comfortable. 
 
 If this flight succeeds, the plane will continue its journey around the world, with Bertrand Piccard taking the controls for the next Pacific crossing from Hawaii to the US mainland. 
 
 The plane will then continue across North America, before attempting to fly over the Atlantic. 
 
 However, the build-up of delays could impact on the later stages. Ideally, the plane needs to cross the Atlantic before August, when the hurricane season reaches its peak. 
 
 Follow Rebecca on Twitter. ||||| CLOSE The Solar Impulse 2 landed in Hawaii Friday, successfully completing a world record-setting 4,000 mile solar powered flight. Jasper Colt, USA TODAY 
 
 The Solar Impulse 2, a sun-powered airplane, circles the Kalaeloa Airport, on July 3, 2015, in Kapolei, Hawaii. (Photo: Marco Garcia, AP) 
 
 The record-setting flight of the sun-powered Solar Impulse 2 landed in Hawaii on Friday after the longest, most dangerous leg of its around-the-world journey. 
 
 The plane landed around noon ET at Hawaii's Kalaeloa Airport after an arduous five-day, non-stop flight, according to Solar Impulse's website, which live streamed the event. 
 
 The completed 4,000-mile leg from Nagoya, Japan, to Hawaii was not only the world's longest solar-powered flight both by time and distance, it also set the record for longest solo flight by time. 
 
 "Just landed in #Hawaii with @solarimpulse! For @bertrandpiccard and I, it's a dream coming true," pilot André Borschberg upon his successful landing. 
 
 Borschberg and Bertrand Piccard have been alternating the long solo flights aboard the plane. The flight from Japan to Hawaii was the eighth of 13 legs. 
 
 Borschberg had been stuck in the cramped cockpit of the plane since taking off early Monday in Japan. He was unable to stand and his only rest was the occasional 20-minute nap. 
 
 The Solar Impulse 2 approaches Hawaii with Andre Borschberg at the controls, near Kalaeloa Airport, O'ahu, Hawaii, on July 3, 2015. (Photo: Solar Impulse) 
 
 
 
 "It is delicate to maintain a balance between my energy and the energy of the aircraft," pilot André Borschberg tweeted early Friday. His only rest the past five days has been occasional 20-minute naps. As the flight neared its destination, the Solar Impulse team tweeted images and videos of the plane over Hawaii. Earlier Friday, founder of Virgin Group Richard Branson congratulated the Solar Impulse team on Twitter for beating Virgin's record non-stop solo flight without refueling. In a tweet Thursday, Borschberg reported on the challenges of the flight. "I'm fighting, it's difficult. ... Managing energy level is not easy. I have to find a hole in the cold front." Unlike the first several legs of the flight, which were over land in Asia, this leg was more dangerous because there would be no place to land if something went wrong above the vast Pacific Ocean. Bad weather delayed the trip to Hawaii for weeks. The plane must find clear skies during the day to receive as much solar energy as possible. At night, running on batteries fueled during the day, the plane descends to a lower altitude and slows speed to conserve energy. Part of the plane's mission is to raise awareness about climate change, showcasing what can be done using nothing but renewable energy. "The most important thing isn't to make world records," Piccard told USA TODAY in an interview last month. "It's to show what we can do with clean technologies," he said, ones that could simultaneously reduce carbon dioxide (CO2) emissions and stimulate economic growth. "We will never improve the situation if we continue to speak of climate change as a big and expensive problem, or by asking people to reduce their lifestyle to protect nature," he said. The mission began March 9 with a flight from Abu Dhabi, United Arab Emirates, to Muscat, Oman. Pilots Borschberg and Piccard have alternated the legs of the journey. The plane's mission control is in Monaco, where a team of meteorologists, flight engineers and other experts closely track and monitor the weather and flight conditions. From Hawaii, the plane will continue the ocean crossing to Phoenix as weather permits. From there, Solar Impulse will land at a location in the Midwest, then in New York City. It will undertake two final flights over the Atlantic Ocean and the Mediterranean Sea before landing back at Abu Dhabi. Contributing: Doyle Rice 
 
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– Round two of the Solar Impulse's toughest leg is under way. After the solar plane's first attempt to cross the Pacific was interrupted a month ago, flight engineers spotted what the Japan Times calls a "possible cloudless stretch." That allowed pilot Andre Borschberg to take off from Japan's Nagoya Airfield at 3:04am local time bound for Kalaeloa, Hawaii. The team announced the plane was to depart only an hour before it did so. Borschberg has since "passed the point of no return," meaning he can't return to Japan if he encounters bad weather, according to the project's website, per the BBC. If successful, the leg will be the longest-duration solo flight in aviation history at 120 hours and the furthest distance flown by a strictly-solar aircraft at 4,900 miles. Prior to starting this leg on a trip around the world, the Impulse 2 had flown about 5,000 miles. Co-pilot Bertrand Piccard is next set to fly the plane from Hawaii to Phoenix before the plane eventually arrives on the eastern seaboard. The Impulse 2 will then attempt an Atlantic crossing, though any further delays could seriously hamper the trip. The team optimally needs to traverse that ocean before the peak of hurricane season in August. The plane had been scheduled to take off from Japan last week, but had to cancel at the last moment due to weather. (Discover how Borschberg will cope during the lengthy Pacific flight.)