The National Aeronautics and Space Administration (NASA) said its X-59 jet under development has completed its first supersonic flight. The Concorde, an earlier supersonic airliner, was pushed out of the market because it produced explosive booms over land when breaking the sound barrier, but this aircraft made only a noise akin to a distant car door closing during supersonic flight. If the X-59 is commercialized as a "quiet" Concorde, it is expected to fly from London to New York in four hours, cutting flight time in half.
NASA said on the 5th (local time) that the X-59, which took off from Edwards Air Force Base in California in the afternoon, climbed to 13,228 meters and reached 1,147 kph. During the flight, a cockpit monitor displayed "M 1.0777." M stands for Mach, a multiple of the speed of sound. Following its first test flight in Oct. last year, this was the first time it broke the sound barrier.
The United States developed a supersonic aircraft in 1947, and the Concorde, built by France and Britain, began its first commercial service in 1976. But the X-59 is the first supersonic aircraft that does not generate ground-level noise even after breaking the sound barrier. Michael Kratsios, the White House science and technology adviser and head of the Office of Science and Technology Policy, said in a statement that "the X-59's first supersonic flight is evidence of America's continued leadership in science, engineering and aerospace innovation."
◇ Sound of a car door closing at 6 meters
At sea level, the speed of sound is 340 meters per second, or 1,225 kph. The claim that the X-59 broke the sound barrier at 1,147 kph that day is because the speed of sound varies with temperature. At sea level, higher temperatures make sound travel faster. The X-59 will soon attempt 1,490 kph at Mach 1.4 at an altitude of 16,764 meters, the actual mission condition.
NASA said, "This speed and altitude will serve as the standard conditions when future supersonic aircraft fly over land," adding, "We will provide X-59 test data to U.S. and international aviation regulators to help set the noise standards needed for future commercial supersonic flights over land."
The Concorde, a supersonic airliner developed by Britain and France, began commercial flights in Jan. 1976 and roamed the Atlantic for 27 years until it was retired in Oct. 2003. Its top speed was Mach 2.04. But supersonic flight was only allowed over the ocean. That is because the Federal Aviation Administration (FAA) banned supersonic flight over land in 1973.
Supersonic flight was not allowed over urban areas because of the sonic boom, the explosive noise created when an aircraft breaks the sound barrier. When an aircraft flies below the speed of sound, its sound (pressure waves) can be heard before it approaches because sound travels faster than the aircraft. When the aircraft breaks the sound barrier, strong shock waves form as newly generated sound piles onto earlier sound before it disperses.
A sonic boom can reach 110 decibels. That is similar to a loud rock concert, so supersonic flight is banned over densely populated areas. NASA said the noise when the X-59 passes overhead is about 75 decibels, quieter than a car door closing 6 meters away.
◇ Dispersing shock waves with an arrowhead nose reduces noise
The X-59 was developed under NASA's Quiet SuperSonic Technology (QueSST) program. Skunk Works, the advanced aircraft development division of U.S. defense contractor Lockheed Martin, led the project. The name dates to 1943, when Lockheed Martin secretly developed the P-80 Shooting Star fighter and researchers worked in a large tent next to a rubber plant with a heavy sulfur stench. The formal name of Skunk Works is Advanced Development Programs (ADP).
So far, $247.5 million (about 379.1 billion won) has been invested in the X-59's development. The reason the X-59 does not produce a sonic boom even after breaking the sound barrier lies in its unique design. The most striking feature is its long, slender nose. Unlike other jets, the nose accounts for one-third of its 30-meter fuselage. The nose was extended thin and long to disperse, not compress, shock waves. The issue is visibility. The cockpit sits low inside the arrowhead-like fuselage, blocking the forward view.
NASA and Lockheed Martin replaced direct vision with a forward display on the cockpit window. Two cameras capture the outside view for this. A camera on the forward canard (small forewing) detects hazards ahead, and a camera under the fuselage provides the imagery needed for landing. Of course, if the cameras fail, small windows on both sides of the cockpit provide some field of view.
To boost commercialization prospects, the X-59 did not use newly developed materials or engines. For example, its engine is the one used in the Saab JAS 39 Gripen, Sweden's 4.5-generation multirole fighter. Instead, unlike other supersonic jets, the engine is mounted above the wing, not underneath. This also helps reduce the sonic boom, because shock waves generated at the wing go upward rather than down toward the ground.
◇ Goal is twice the speed and altitude of conventional airliners
Director General Jared Isaacman of NASA said on the day of the X-59's supersonic breakthrough, "Since the first flight of the X-59 on Oct. 28, 2025, the research team has made tremendous progress," adding, "We have flown 16 times in the past 90 days, settling into a steady testing rhythm."
NASA's ultimate goal for the X-59 is to reach Mach 1.6, or 1,700 kph, at an altitude of 18,288 meters. That corresponds to twice the speed and cruising altitude of conventional airliners. At sea level, that would be 1,960 kph. If it currently takes about eight hours to fly from London to New York, that could be cut to four hours if the X-59 evolves into a quiet Concorde.
To date, only two supersonic aircraft have entered commercial service. One was the Concorde, and the other was the Tupolev Tu-144, built by the former Soviet Union. Developed by the Soviet design bureau Tupolev, it became the world's first supersonic airliner and completed its maiden flight on Dec. 31, 1968. But due to safety issues, it only operated from 1975 to 1978.
NASA's initial goal was to use the X-59 to persuade the International Civil Aviation Organization (ICAO) and the U.S. FAA to accept overland supersonic flight in the late 2020s. The day is approaching when a quiet Concorde will fly overhead faster than sound.
References
NASA, https://www.nasa.gov/aeronautics/x-59-first-supersonic-flight/
American Institute of Aeronautics and Astronautics (AIAA), https://aerospaceamerica.aiaa.org/features/nasas-boom-buster/