When Boom Supersonic's XB-1 broke the sound barrier last month, it achieved commercial supersonic flight for the first time since the Concorde. It also did it without an audible sonic boom, which could pave the way for the first cross-country supersonic flights.
Usually, when an aircraft goes supersonic, exceeding Mach 1, the resulting shockwave creates a continuous sonic boom. The explosive sound of sonic booms can startle humans and animals and cause property damage. Sonic booms were a contributing factor in the retirement of the Concorde as countries, including the United States, prohibited supersonic flight over inhabited areas.
The XB-1, however, achieves a "boomless cruise" by utilizing a phenomenon called "mach cut off," where the sound waves are refracted upwards, and the sonic boom never reaches the ground. The idea behind mach cutoff has been around since the 1960s, but the phenomenon only occurs at the correct altitude and speed for atmospheric conditions, requiring computing power unavailable in the Concorde era.
Current regulations do not exempt boomless supersonic flight from the ban on overland supersonic travel. If allowed in the future, Boom promises flights from New York to San Francisco in three and a half hours.
Previously: NASA reveals secret supersonic airplane that quiets the sonic boom to a thump
