Veteran pilot tested to the limit of endurance on record-breaking solar-powered flight across the Pacific, on the eighth leg of round-the-world journey 
 
 A solar plane attempting the world’s first flight around the globe has landed in Hawaii, after breaking the record for the longest non-stop solo flight in history. 
 
 Solar Impulse 2, piloted by the Swiss pilot André Borschberg, took off from Nagoya in Japan at 3am on Monday, for the five-day crossing of the Pacific Ocean, the riskiest leg of its journey. 
 
 At 72 hours into the eighth leg of its 22,000-mile circumnavigation, Borschberg broke the endurance record for a solo flight. 
 
 “The next leg is what I call the moment of truth,” he told the Guardian before departing. “The first time we fly many days, many nights with a solar-powered airplane, the first time that we fly over the ocean, the first time that one pilot flies alone for so long. We are exploring new territories.” 
 
 Borschberg is sharing the round-the-world attempt, completing alternate legs with his co-pilot Bertrand Piccard, who will now fly the single-seater plane on a 100-hour leg to Phoenix, Arizona, in the US. 
 
 Saving power is key to the journey’s success, as the plane – fitted with 17,000 photovoltaic solar cells – must reach heights of 9,000 metres during the day so that it can glide through the night. At top speed, it reaches 87mph. 
 
 “There’s a lot of uncertainty at the end; we cannot know everything,” said Piccard, before the flight took off on Monday. 
 
 During the 5,079-mile leg, Borschberg has spent about four days, 21 hours and 51 minutes in the air and throughout the journey has only been able to rest in 20-minute intervals. 
 
 The 62-year-old veteran pilot and engineer has had to endure temperatures close to 37C (100F) in the cockpit. He said that yoga had been a “huge support” for sustaining a positive mindset and helped to keep him alert. Tweeting throughout the journey, Borschberg said on Thursday that the fourth day of this leg had been tough, after he “climbed the equivalent altitude of Mount Everest four times”. 
 
 The historic journey has been set back multiple times since first taking off from Abu Dhabi in March. 
 
 André Borschberg (@andreborschberg) During the fourth day I felt very tired, having climbed the equivalent altitude of Mount Everest four times pic.twitter.com/N6Wk1vi9ok 
 
 It had been stalled in Nagoya for weeks due to bad weather, waiting for a suitable five-day window of clear weather to complete the journey. The original flight was diverted from China in June. 
 
 On the most recent leg, there were concerns that Borschberg would have problems crossing a cold-weather front before Hawaii, ahead of the home straight over the Pacific archipelago. ||||| 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 
 
 Read or Share this story: http://usat.ly/1LZ4mxU ||||| Editor's Note: Four weeks after the original planned departure, Solar Impulse 2 took off from Nanjing on Saturday, May 30, bound for Honolulu. A dangerous cold front forced pilot André Borschberg to land at Japan's Nagoya Airfield, where the team will wait for better weather conditions to resume the journey across the Pacific. 
 
 On Saturday, a single-seat, solar-powered plane with a wingspan longer than that of a Boeing 747 took off from Nanjing, China, headed for Honolulu. For a normal passenger jet, that's about a 12-hour flight. Solar Impulse 2 , the 5,000-pound plane powered by nothing but sunshine, was supposed to take five days, before the a nasty cold front forced it to abort the flight and land in Japan.^1^ 
 
 This is by far the hardest part of the plane's journey around the world, which started in Abu Dhabi last month, and should finish there in August. Swiss pilots Bertrand Piccard and André Borschberg have been working up to this for 12 years, and they're fully aware of how trying it will be. 
 
 It's very interesting how the human mind can adapt to this type of new situation. Pilot Bertrand Piccard 
 
 "If we are optimistic, we will say that we've done six legs out of 12," Piccard says. "And if we are pessimistic, we will say have have traveled 8,000 kilometers out of 35,000." 
 
 Which is to say, things are going according to plan, but there's much left to do, including the flight to Honolulu, then a 3,000-mile leap over the rest of the Pacific to Phoenix, Arizona. 
 
 The trick to staying aloft for days at a time is straightforward. The solar panels that cover the wings and fuselage of Solar Impulse 2 charge four extra-efficient batteries, which power the 17.4-horsepower motors. You charge up when the sun's out and cruise at up to 28,000 feet. At night, you drop to about 5,000 feet, converting altitude into distance. 
 
 There are two factors that make the Pacific crossing especially challenging: The ocean's size and the pokey speed of the plane (try 20 to 90 mph) mean each pilot will need to spend four or five days and nights aloft to reach land, in a cockpit that resembles a tube hotel in miniature. The second problem is the weather: Solar Impulse 2 needs pretty specific conditions to takeoff, cruise, and land—and that all needs to be planned out five days in advance. 
 
 Borschberg is scheduled to take off from Nanjin on May 7, at the earliest. If the flight goes as expected, he will take five days to make the trip to Honolulu. Then Piccard will make the four-day trip to Phoenix. 
 
 André Borschberg has spent 72 hours at a time in a simulator to prepare for this flight. Niels Ackermann/Rezo.ch/Solar Impulse 
 
 Pilot Preparation 
 
 It doesn't sound like much fun: There's no walking around, or even standing up in, the 135-cubic foot cockpit. The cabin is neither heated nor pressurized, though it is insulated. 
 
 To get used to the cramped conditions, the pilots have spent long stretches in a simulator. They use meditation, breathing exercises, and whatever yoga they can manage to keep their bodies and minds feeling as fresh as possible. 
 
 Piccard and Borschberg will sleep in 20 minute stretches (the aircraft has autopilot functions and there's not much to collide with over the Pacific), six to eight times a day. It's hardly a good night's rest, but it's enough to get by, and the seat fully reclines. They have an alarm set to wake them up, but their bodies have gotten used to the routine, and don't really need it, Piccard says. "It's very interesting how the human mind can adapt to this type of new situation." 
 
 The grub sounds pretty good, especially for air travel: Nestlé made special meals that can survive temperatures from -4 to 95 degrees Fahrenheit. There's mushroom risotto, chicken with rice, and potatoes with cream and cheese. "It's very nice," Piccard says. The toilet, FYI, is built into the seat. 
 
 It may seem difficult to stay focused when you've seen nothing but ocean for days on end, but it's not a major concern to the pilots. "There's quite a lot of things to do," Borschberg says. More importantly, they've been working up to this for more than a decade. They're jazzed. 
 
 Of course, they've got to be ready for things to go wrong. In the event of a sudden catastrophe, like an engine or battery fire, they've trained for bailing. If cloudy weather stops the panels from charging the batteries adequately, Piccard and Borschberg will take their time putting on the dry suit, preparing the parachute, alerting mission control, and switching on an emergency beacon. "You get out very peacefully," Piccard says. 
 
 They key in any situation is getting away from the plane—there's a serious risk of electrocution when you fly a pile of electronics and batteries into the ocean. Then you settle into your life raft, because you're thousands of miles from land, and major shipping lanes, it may take two or three days to be picked up. 
 
 The cockpit of Solar Impulse 2 resembles a tube hotel, in miniature. Solar Impulse/Pizzolante 
 
 The Weather Game 
 
 There's a lot to take into account, says team meteorologist Luc Trullemans. Routes are decided using radar and satellite data, and flight simulations. Equipment from engineering consultancy Altran and a team mathematician lend a hand. Cloudy skies mean the solar panels can't recharge the batteries. Wind conditions are crucial: Tailwinds are best, and the team will tolerate cross tailwinds up to 45 degrees (90 degrees would be blow fully sideways). Headwinds are a problem for a plane with limited power: Between Myanmar and Chongqing, China, Piccard found himself flying backwards at one point. 
 
 The six legs of the Solar Impulse 2 journey already completed have been relatively short affairs, between 15 and 20 hours. That's not so tricky to plan, because at the time of takeoff, you have an excellent idea of what the weather will look like for the whole flight. 
 
 All that gets way more difficult now, because the team can't predict the weather with the accuracy it wants more than three days in advance. "We must be 100 percent certain with our weather forecasts for the first three days of the flight and of course, the takeoff conditions," says Trullemans. After that, the route can always be changed ... on the fly ... but major deviations are best avoided. The plan is to keep a sharp eye on coming conditions. The pilot can fly to the north or south to avoid a cold front, for example. 
 
 Beyond that, you hope for the best: Tailwinds, clear skies, and no need to inflate that life raft. 
 
 ^1^Story updated Monday, June 1 at 12:25 EST to include Solar Impulse 2′ s early landing in Japan.
– A solar plane made aviation history today, and its historic journey is nowhere near over. The Solar Impulse 2, controlled by Swiss pilot André Borschberg, landed in Hawaii after a five-day, 4,000-mile trip over the Pacific Ocean from Japan, reports USA Today. The feat is just one leg on a planned around-the-world trip, but the non-stop stretch over the Pacific was seen as the most difficult, and dangerous, part of the flight. It set the record for the longest solar-powered flight in terms of both time and distance. Waiting to greet Borschberg at the Kalaeloa Airport were his family and his co-pilot, Bertrand Piccard, who will now fly the plane on its next leg, a 100-hour trip to Phoenix. The 62-year-old Borschberg had to make do with 20-minute naps in the cramped cockpit over his five-day trip, and at times, he sweated through 100-degree temperatures, reports the Guardian. He tweeted along the way, crediting yoga for helping his mental and physical stamina, especially yesterday, when he “climbed the equivalent altitude of Mount Everest four times." CNN explains that the aircraft is covered in 17,000 solar cells, which collect the sun's rays during the day and allow the plane to fly through the night on battery power.