The US banned supersonic flight in 1973, partly because of the noise, partly because US plane builders had decided they didn’t want to compete with Concorde. However, NASA kept working on the boom problem, developing new understanding of how sonic booms form and propagate, and in turn technologies which might mitigate these.Last week Boom Supersonic announced they wanted to get the FAA rules modified to be based on sound levels, rather than sound speeds, and now NASA is gearing up to fly their X-59 Quiet supersonic test aircraft.