Solar Impulse 2, the pioneering aircraft known for the first round-the-world solar flight, was lost during an uncrewed flight, ending its decade-long journey in the skies. The experimental aircraft crashed into the Gulf of Mexico on May 4 after losing power during an autonomous test flight, according to a report by the National Transportation Safety Board. There were no fatalities or injuries. The loss of the unconventional aircraft marks the end of an inspiring attempt to promote clean energy and push the boundaries of aviation. Around the world Swiss psychiatrist Bertrand Piccard and entrepreneur André Borschberg developed Solar Impulse 2 in 2015 after co-piloting the first non-stop balloon flight around the world. The two aviators set out to complete the first circumnavigation of Earth using only solar power and draw attention to sustainable energy technologies. The carbon-fiber aircraft stretched across 232 feet (70 meters) and weighed only 5,100 pounds (2,313 kilograms).…