Solar Impulse 2: round-the-world trip on hiatus

The adventurers' plane, the Solar Impulse 2, took off from Abu Dhabi on March 9. The plan was for 12 legs with a total length of about 35,000 kilometers. They wanted to complete it in 25 days. But upon landing on the Hawaiian island of Oahu, the pilots discovered the plane's solar batteries had overheated and were severely damaged. The repair work will take several months.

The plane is stuck at Kalaeloa airport, from where Piccard and Borschberg hope to continue their journey in April 2016. It's not the first unplanned stop. In June a cold front forced the pilots to interrupt their flight from Nanjing in China on day two of their seventh leg. For weeks, they had to wait for better weather in Nagoya, central Japan, before they could cross the Pacific to Hawaii.

Piccard (left) is actually a psychiatrist, according to his university degree. And Borschberg is an engineer. For the longer stretches taking the two over entire oceans, they have had to come with strategies, like yoga for instance.

In contrast to modern airliners, Solar Impulse 2 is not exactly weather-proof - as the explorers experienced. The plane can only start once the green light has been given by a control center set up in Monte Carlo. Sand storms, heavy rain and winds, snow or a cold front like the one they encountered in Japan can bring the project down.

A stream of information from the plane keeps the team in Monte Carlo in the loop. Ground control knows how the batteries and the two pilots are doing at all times.

Solar Impulse 2, as the name suggests, is the second attempt by Piccard and Borschberg. This time around, the pilots have more room in the cockpit, and the plane has a more modern, lighter construction and more innovative solar tech.

Solar Impulse 1, at a weight of 1.6 tons, had a tiny cabin for only one pilot. Each wing had a surface area of around 64 square meters (688 square feet). Its successor weighs 2.3 tons. That seems heavy in comparison, but an Airbus 340 weighs more than 125 tons.

The immense wingspan of the SI2 - 72 meters or 236 feet - has its advantages: around 17,000 solar cells have been installed. They provide the plane's four motors and propellers with power to reach top speeds of 140 kilometers (87 miles) per hour, at a maximum height of 8,500 meters or almost 30,000 feet.

The overarching goal of the mission is to promote green energy around the world, says Piccard. He's certain that one day solar-powered planes will revolutionize the aviation industry - carrying hundreds of passengers per flight.