By Leo Kelion, Technology reporter, BBC Neal Stephenson is thinking big – 20km (12.4 miles) big, to be precise. That’s how high the tower he has proposed building will soar if the project ever comes to fruition. Such a structure would make it cheaper to launch objects into space, he says, thanks to fuel savings. It’s a lofty goal. But creating a building more than 24 times taller than Dubai’s Burj Khalifa and not far off double the height commercial aircraft fly at is no easy task. “It ends up being all about ...