Solar Impulse 2, an ambitious plane flying around the world using nothing but solar power, is preparing to take off again today after a nine-month delay.

The aircraft, which has a wingspan of 72 meters (236 feet) and has 17,000 solar cells on its wings, was grounded in Hawaii in July 2015, when the seasonal changes meant there was no longer enough sunlight to continue its journey, in addition to a problem with the plane’s batteries. Today, with the added sunlight of spring and summer, the mission has now resumed.

The project is the brainchild of André Borschberg and Bertrand Piccard, both from Switzerland, who are taking it in turns to fly the single-seater vehicle.

“As we experienced many times with Solar Impulse, obstacles often turn out to be opportunities for improvement,” said Borschberg in a statement. “Ultimately, this time was used to recreate the strong mindset within the team to continue our adventure. It takes sometimes more time to build up the right spirit then to develop new technologies.”

 

 

^{You can watch a live stream from the cockpit above}

Despite its size, the plane is as light as a car, making flying it quite difficult. To complete its round the world trip, the plane has been making pit stops in various countries along the way. It began in Abu Dhabi in March 2015, before visiting Oman, India, Myanmar, China, Japan, and now the United States. The round the world trip has been broken into 12 legs, varying in flight time from several hours to up to five days. 

The aircraft is now beginning one of the most treacherous flights of its journey, a 3-day trek from Hawaii to Mountain View, California. Piccard is expected to touch down on Saturday morning.

Solar Impulse 2 was designed to showcase the possibilities of solar power, in a world that is increasingly realizing the importance of renewable energy. Both the founders believe that solar power can contribute to a clean future on Earth, and they are using this rather lavish public relations stunt to get that point across.

“Thank you to the whole #solarimpulse team all over the world for making my dream a reality!” Piccard, who is flying this leg of the trip, tweeted before take off.

^{Shown are the routes the plane may take. Solar Impulse/Flickr}

The plane itself is a marvel of engineering. Despite its array of solar panels, it has a rather minimal source of power, with a top speed of just 138 km/h (86mph). To take off, it actually needs people on bikes to essentially give it a push start. Any moderate to high wind also makes take-off dangerous, so the team often wait for periods of quiet.

During the flight, the pilots are monitored by a team at mission control in Monaco. Inside, to save on weight (the entire plane weighs just 2.3 tonnes), the pilots operate with very limited resources. There is no autopilot, so the only time to rest that they get are short 20-minute “cat naps," even on the multi-day flights, while a lack of heating means they must keep themselves wrapped up warm. Food comes in the form of pre-packed meals, and going to the toilet involves using a rather unenvious hole in their seat.

The plan is to land in two more locations in the U.S. this year, before a daunting final leg crossing the Atlantic and ending in either southern Europe or north Africa. But despite the delays, the mission will have been a considerable success if and when it is completed.

Here’s hoping it makes it to its final destination safe and sound. You can be sure we’ll be tuning in along the way.

^{Images via Solar Impulse/Flickr}