Solar Impulse 2 flies over the Golden Gate Bridge in San Francisco at the end of its journey from Hawaii, part of its attempt to circumnavigate the globe, on April 23, 2016. #

Engineers work on the carbon-fiber 72-meter-long wing of Swiss sun-powered aircraft Solar Impulse HB-SIB on December 17, 2013 at the former military airport of Duebendorf, near Zurich. #

Swiss scientist-adventurer and pilot Bertrand Piccard sits in a near-exact reconstruction of the cockpit of the sun-powered aircraft Solar Impulse HB-SIB at the beginning of a non-stop 72 hours simulation test flight inside on December 17, 2013. The goal of the experience is to prepare Piccard and pilot Andre Borschberg for their upcoming long-duration round-the-world flights. #

Switzerland's Andre Borschberg (L) and Bertrand Piccard (R), Solar Impulse founders and pilots, present the new Monaco Solar Impulse control center, on February, 10, 2015, in Monaco. #

German test pilot Markus Scherdel lands the new experimental aircraft "Solar Impulse 2", after its first flight at the airbase in Payerne, Switzerland, on June 2, 2014. #

The cockpit of the solar-powered Solar Impulse 2 aircraft, after a training flight at its base in Payerne on November 8, 2014. From left to right instruments are : fuses, throttle, power management, autopilot, motor control, flying instruments and telecommunication. #

"Solar Impulse 2" descends to land in Muscat on March 9, 2015. Two pilots attempting the first flight around the world in a solar-powered plane began the maiden leg of their voyage. The aircraft took off from Abu Dhabi in the United Arab Emirates to start a five-month journey organized to focus the world's attention on sustainable energy. #

From left: Deniz Borschberg, the son of the Swiss pilot flying the Solar Impulse 2, Bertrand Piccard, the initiator, chairman and one of the pilots of Solar Impulse 2 and Solar Impulse mission director Raymond Clerc sit at the Mission Control Center in Monaco on June 1, 2015, as the Solar Impulse 2 makes its landing in Japan. #

Picture taken by Swiss adventurer Andre Borschberg onboard Solar Impulse 2 during the flight from Tusla, Oklahoma, to Dayton, Ohio, shows the Mississippi River at sunset on May 21, 2016. #

The Nagano mountain area is pictured by Swiss pilot Andre Borschberg in the cockpit of the Solar Impulse 2 plane during the 7th leg of the round the world trip in this June 1, 2015 photograph released by Solar Impulse. #

An image shot by pilot Bertrand Piccard of Solar Impulse2 during the flight over the Red Sea during the last leg of the round the World trip prior to landing in Abu Dhabi to finish the first around the world flight without the use of fuel on July 23, 2016. #