Dr. Lou Povinelli talked about the state of NASA fundamental high-speed research. Although America was the home to the first manned supersonic flight since 1947, there are still no commercial aircraft speeding over our heads today. In fact, one cannot even find such flights occurring anywhere in the world currently. If such a technology could deliver a person from coast to coast in less than 4 hours and effectively make the globe even smaller, why does it not exist today? The reason one does not see such supersonic transports in the U.S. or any other country is mostly based on the current ban on supersonic flight over land in the United States. The sole endeavor into supersonic commercial flight, the Concorde, was partially doomed due to the prevention of any New York-to-Los Angeles flights. The law exists due to the unnerving nature of hearing a supersonic boom on the ground.
Current research being conducted amongst all of the NASA aeronautics Centers, hopes to mitigate the sonic boom effects through specialized designs that could result in tolerable sound levels for overland flight. Most of the work is in creating Computational Fluid Dynamics (CFD) tools which can simulate the shock structure and noise characteristics created by aircraft body, as well, as the engine exhaust jet. The overall idea of minimizing apparent ground noise for such an aircraft is to overlay the paired expansion that goes with each shockwave on top of another shock to minimize its effect. Comparison between old supersonic designs such as the Concorde and newer designs currently under development on by NASA can be seen in the pressure rise illustrated in the figure below.
As can be clearly observed, the pressure rise and subsequent fall do not have the same magnitude and, also, do not occur as sharply as in previous designs in which minimal effort was made to limit the boom.
NASA has long-term goals set for the supersonic aviation industry over the next 20+ years. In the next three years, NASA expects the introduction of a supersonic business jet, which is not out of the question, considering that Gulfstream has been working on supersonic projects for the last 15 years. After that, one expects a small airliner capable of carrying 35-70 passengers by 2020 and a large transcontinental airliner is expected by 2030. These are bold goals, but NASA is taking all the right steps to push the frontiers of science on these goals to become a reality.