QUESTION: Why are there two booms when the Shuttle re-enters? ANSWER from Jenny Lyons on August 12, 1997: Sonic booms are created by the shock waves that form when an aircraft passes through the sound barrier (in other words, when its velocity is greater than the speed of sound). During its descent from space, as the Orbiter goes from supersonic speeds (greater than Mach 1) to subsonic speeds (less than Mach 1), shock waves are formed due to the air being compressed along the wing leading edges. These shock waves produce the noise of a sonic boom. As I understand it, the reason the Orbiter creates a double sonic boom when it's flying at such speeds is because of the shape and sweep of its wings. It's specific delta wing configuration creates two shock waves instead of just one; and therefore two sonic booms.