In the heady days after the end of World War II, back when NASA was NACA (the National Advisory Committee for Aeronautics), going faster than sound meant finding a willing pilot, building a capable plane, and then tearing up an empty swath of sky over a vast and unpopulated desert.

Chuck Yeager did it first, in a loud NACA plane called the Bell X-1. From there, it was a short leap to jet fighters, the most common form of supersonic craft today.

In the war theaters and training grounds where supersonic fighters operate, their supersonic booms are at most a secondary concern. No one's worried about noise pollution when bombs are falling. But turning that innovation, the ability to travel faster than sound, into a viable, commercial business? That's a harder project, and one far more bound up with problems of noise than it is with the physical limitations of existing craft.