When André Borschberg started flying as a 15 year old, he didn’t worry about how much fuel he had to burn to get and stay aloft. These days, it’s pretty much all he thinks about. It has been three years since Borschberg and Bertrand Piccard completed an around-the-world journey in Solar Impulse 2, the sun-powered plane that could stay aloft for days at a time. That aircraft was remarkable but impractical: It had the wingspan of a Boeing 747, but maxed out around 90 mph and its cockpit was so cramped that the pilots (who alternated legs of the journey) used a toilet built into the seat.
