Forty-four years ago over Oklahoma City, the US government conducted a curious experiment. During a six-month period, Air Force planes produced 1,253 sonic booms during daylight hours to observe the noise effects on populated areas. At the time, supersonic airliners were promised as the next big thing in civil aviation, and the goal of the tests was to determine if people could grow accustomed to the loud bangs produced by aircraft breaking the sound barrier on a daily basis.
The tests didn't go well. Though residents were amenable at first — city officials had campaigned to be the test region — complaints and damage reports exploded after the first few weeks and the program ended six months early. Public opposition to sonic booms only grew from then on, leading aviation giants like Boeing to abandon plans to build supersonic aircraft. Though the Anglo-French Concorde did make it off the drawing board, regulations against sonic booms over land ultimately limited the aircraft to flying only over the Atlantic Ocean when it began carrying passengers in 1976.
But come this November, NASA will reopen the booming debate as part of its partnership with Lockheed Martin to build a test aircraft that'll fly with a quieter sonic boom. Though the Low-Boom Flight Demonstrator (its official designation will be the X-59 QueSST) won't fly until 2022, November's tests will use an existing F/A-18 to produce a sonic boom similar to the predicted sound level of X-59 QueSST.
During the tests, which'll be held over the Gulf of Mexico off Galveston, Texas, the F/A-18 will dive from almost 50,000 feet and go briefly supersonic before leveling off at about 30,000 feet. The sonic boom produced from the dive should sound more like a car door slamming (NASA calls it a "sonic thump") as opposed to the thunderous noise produced by existing supersonic aircraft.
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The agency will gauge the noise level from the boom using sensors on the ground and collect responses from public volunteers. In a press release Friday announcing the tests, NASA said it hopes to get a different response from what happened in Oklahoma. "The result [of the tests] in that area: a pair of quiet sonic booms — soft thumps, really — which people on the ground, including those NASA researchers and resident volunteers, might barely notice, if they hear anything at all."
NASA and Lockheed Martin say the X-59 QueSST's shape — it has a long pointed nose, sharply swept wings and raked canards (small wings positioned forward of the main wings) — will ensure that the individual pressure waves the airplane produces at speeds faster than Mach 1 never converge and cause a traditional sonic boom. If the design is successful (NASA also will test the X-59 QueSST over additional US cities) NASA hopes aircraft manufacturers will the use technology to bring supersonic flight back to the public.
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