Boom’s headquarters, a gleaming white hangar in a suburb of Denver, bustles with activity. In one corner, a team assembles a mock-up of the Overture’s interior, which features wide seats, wood trim, and a locker under each berth instead of an overhead bin. Not far away, engineers stress-test the carbon-fiber horizontal stabilizer—that’s the little winglet on a plane’s tail—of the XB-1 demonstrator. A growing collection of parts, including a pile of Goodyear aircraft tires, fills one room. Here and there you see models of the airliner, ambitiously sporting the liveries of carriers from around the world. At 170 feet long, the jet will be a bit shorter than a Boeing 777. With a pinpoint nose and triangular delta wing that spans just 60 feet, it will look like a dart. A full-size mock-up of the demonstrator, which will carry two people at 1,400 mph, sits in the middle of the hangar.