The full article truncates the reference to the flight altitude, which can be important. For a high enough altitude and a low enough supersonic Mach number, the temperature profile of the atmosphere can cause the shockwave to become subsonic (and vanish) before it reaches the ground.
Once upon a time, in the misty past of the 1970s, on a spring day on campus, a fellow student and I noted a distant contrail proceeding at what seemed a very high speed relative to what we were used to seeing. We assumed it was a military flight, not a commercial one, which suggested an altitude of about 50,000 feet. By doing our best to estimate the angular motion rate, we calculated the speed to be about Mach 3, which would have been consistent with an SR-71. No sonic boom. If you are high enough, the shockwave overpressure diminishes with distance. Ever since then, I have wondered whether the problem of the supersonic transport sonic boom results from too low a cruise altitude.
The full article truncates the reference to the flight altitude, which can be important. For a high enough altitude and a low enough supersonic Mach number, the temperature profile of the atmosphere can cause the shockwave to become subsonic (and vanish) before it reaches the ground.
Once upon a time, in the misty past of the 1970s, on a spring day on campus, a fellow student and I noted a distant contrail proceeding at what seemed a very high speed relative to what we were used to seeing. We assumed it was a military flight, not a commercial one, which suggested an altitude of about 50,000 feet. By doing our best to estimate the angular motion rate, we calculated the speed to be about Mach 3, which would have been consistent with an SR-71. No sonic boom. If you are high enough, the shockwave overpressure diminishes with distance. Ever since then, I have wondered whether the problem of the supersonic transport sonic boom results from too low a cruise altitude.