Science & Environment

Solar Impulse aims for Pennsylvania

Cockpit Image copyright Solar impulse
Image caption This is Bertrand Piccard's last leg before he makes the Atlantic crossing

The sun-powered aircraft Solar Impulse has taken off from Dayton, Ohio, on a 750km flight to Lehigh Valley in Pennsylvania.

The journey is the 13th leg in a quest that started in Abu Dhabi last year to circumnavigate the globe on zero fuel.

Swiss adventurer Bertrand Piccard is in the pilot's seat.

Mission controllers expect the 72m-wingspan, electric plane to complete the stage in about 17 hours.

The aircraft took off from Dayton International Airport just after 04:00 local time (08:00 GMT).

Getting to Lehigh Valley will position the project to make its entry into New York in the coming days.

The "Big Apple" is set to be the base for Solar Impulse as it waits for a weather window to fly the Atlantic.

Deciding when to cross the ocean will be a tricky decision. The slow-moving, ultra-light plane needs benign winds, and the team concedes that the right conditions may not present themselves for several weeks.

Image copyright SOLAR IMPULSE

Wednesday's flight to Lehigh Valley was postponed for 24 hours for checks on the aircraft following a power problem in its mobile hangar.

The air fans that hold up the inflatable structure briefly failed on Tuesday, allowing the canvas to collapse and touch the plane's fuselage and the wings.

Once engineers had concluded that Solar Impulse had not been affected in anyway, they cleared the mission to resume.

It means the plane has departed Dayton just as poor weather approaches from the west.

The hop to New York will likely occur next week, after the Memorial Day weekend.

Although it is a short distance from Lehigh Valley to John F Kennedy Airport, the time taken to complete the leg will be extended by two factors.

One is the desire to fly around the Statue of Liberty to take some pictures; the other will be the wait for air traffic controllers to find a landing slot at one of the busiest airports in the world.

"It's going to be a long flight - more than 26 hours. But it's going to be extraordinary because it will be so symbolic to be at [the Statue of Liberty]," said Andre Borschberg, who will pilot the stage.

"I was just visiting the Wright Brothers museum here in Dayton, and one of the flights he did - I think it was Orville - was the first airplane flight over the Statue of Liberty. He didn't have to deal with co-ordinating the traffic because he knew there was nobody else, no other airplane flying at the time!"

Image copyright SOLAR IMPULSE
Image caption Engineers had to be sure that the mobile hangar had not inflicted any damage

The project has made excellent progress since renewing its global challenge a month ago in Hawaii.

From Kalaeloa in the central Pacific, it flew to Mountain View, California; and from there it reached across to Phoenix, Arizona, then to Tulsa, Oklahoma, before landing in Dayton on Saturday.

In 2015, Solar Impulse flew eight stages from Abu Dhabi to Kalaeloa, including a remarkable 4-day, 21-hour leg over the western Pacific - the longest (time duration) flight in aviation history.

It was damage to its batteries on that stage, however, that forced Solar Impulse to lay up for 10 months, for repairs and to wait for optimum daylight length in the northern hemisphere to return.

LEG 1: 9 March. Abu Dhabi (UAE) to Muscat (Oman) - 772km; 13 Hours 1 Minute

LEG 2: 10 March. Muscat (Oman) to Ahmedabad (India) - 1,593km; 15 Hours 20 Minutes

LEG 3: 18 March. Ahmedabad (India) to Varanasi (India) - 1,170km; 13 Hours 15 Minutes

LEG 4: 18 March. Varanasi (India) to Mandalay (Myanmar) - 1,536km; 13 Hours 29 Minutes

LEG 5: 29 March. Mandalay (Myanmar) to Chongqing (China) - 1,636km; 20 Hours 29 Minutes

LEG 6: 21 April. Chongqing (China) to Nanjing (China) - 1,384km; 17 Hours 22 Minutes

LEG 7: 30 May. Nanjing (China) to Nagoya (Japan) - 2,942km; 1 Day 20 Hours 9 Minutes

LEG 8: 28 June. Nagoya (Japan) to Kalaeloa, Hawaii (US) - 8,924km; 4 Days 21 Hours 52 Minutes

LEG 9: 21 April. Kalaeloa, Hawaii (US) to Mountain View, California (US) - 4,523km; 2 Days 17 Hours 29 Minutes

LEG 10: 2 May. Mountain View, California (US) to Phoenix, Arizona (US) - 1,199km; 15 Hours 52 Minutes

LEG 11: 12 May. Phoenix, Arizona (US) to Tulsa, Oklahoma (US) - 1,570 km; 18 Hours 10 Minutes

LEG 12: 21 May. Tulsa, Oklahoma (US) to Dayton, Ohio (US) - 1,113 km; 16 Hours 34 Minutes

LEG 13: 25 May. Dayton, Ohio (US) to Lehigh Valley, Pennsylvania (US)

LEG 14: June. Lehigh Valley, Pennsylvania (US) to New York (US) and follow me on Twitter: @BBCAmos