Research into minimizing the sonic boom that occurs as an aircraft flies at Mach 1 and beyond is continuing at NASA and commercial aircraft makers. Efforts to modify the N-wave, the shock wave which occurs at speeds in excess of Mach 1, have been ongoing at Gulfstream, in conjunction with NASA. Using a modified F-15B fitted with a telescoping boom flight tests have been promising creating a smaller n-wave which will greatly reduce the noise heard on the ground from “sharp crack to a quiet whisper” according to a presentation which Gulfstream gave to the FAA sponsored Advanced Technologies and Supersonics symposium in 2009. The boom, which can extend to 24 feet from its 14 foot-long retracted position, is constructed using composite materials. According to Gulstream, the Quiet Spike, results ” in a softer sound that is 10,000 times quieter than the Concorde.”
In 2005, Lockheed patented “Passive aerodynamic sonic boom suppression for supersonic aircraft” which also addresses the area of the aircraft’s nose as a way to mitigate the pressure wave propagating from the airframe. A gull wing, as well as modified body form created by pinching the fuselage at the mid-point also is identified to reduce noise.
In 2008, the FAA issued a statement indicating that it would be open to new rules allowing for the operation of supersonic aircraft while over land. This change, would allow supersonic operation of aircraft meeting Stage 4 sub-sonic noise requirements. Currently, supersonic aircraft which meet this noise threshold cannot operate in the US.