The National Aeronautics and Space Administration (NASA) said its X-59 jet under development succeeded in its first supersonic flight. The Concorde, a past supersonic airliner, was forced out of the market because it created explosive sounds on the ground when breaking the sound barrier, but this aircraft produced only a sound like a car door closing in the distance during supersonic flight. If the X-59 is commercialized as a "quiet" Concorde, it is expected to cover the route from London to New York in four hours, cutting flight time in half.
NASA announced that on the afternoon of the 5th (local time), the X-59 that took off from Edwards Air Force Base in California climbed to 13,228 meters and reached 1,147 kph. During that time, a display reading "M 1.0777" appeared on the monitor in front of the cockpit. M means Mach, a multiple of the speed of sound. Following its first test flight in Oct. last year, it broke the sound barrier for the first time on this day.
The United States had already developed a supersonic aircraft in 1947, and the Concorde developed by France and the United Kingdom began its first commercial service in 1976. But the X-59 is the first supersonic aircraft that does not generate noise on the ground even after breaking the sound barrier. Michael Kratsios, the White House science and technology adviser and director of the Office of Science and Technology Policy, said in a statement that "the first supersonic flight of the X-59 is evidence of America's continued leadership in science, engineering and aerospace innovation."
◇ The sound of a car door closing at 6 meters
The speed of sound at sea level is 340 meters per second, or 1,225 kph. The reason the X-59 is said to have broken the sound barrier at 1,147 kph that day is that the speed of sound varies with temperature. Sea level has a higher temperature, so sound travels faster. The X-59 will soon aim for 1,490 kph at Mach 1.4 at an altitude of 16,764 meters, the actual mission condition.
NASA said, "This speed and altitude are the conditions that will serve as the standard when future supersonic aircraft fly over land," adding, "We will provide X-59 test data to U.S. and international aviation regulators to help establish noise standards needed for future commercial supersonic flights over land."
The Concorde, a supersonic airliner developed by the United Kingdom and France, began commercial flights in Jan. 1976 and crisscrossed the Atlantic for 27 years until it was retired in Oct. 2003. The Concorde's 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 could not be conducted over city centers because of the sonic boom, a deafening noise generated when an aircraft breaks the sound barrier. When you see an aircraft flying below the speed of sound, you hear the sound (pressure waves) before it gets close. That is because sound travels faster than the aircraft. When an aircraft breaks the sound barrier, a strong shock wave is created as newly generated sound piles on top of previously generated sound before it can dissipate.
A sonic boom can reach 110 decibels (a unit of sound level). That is about the level of a loud rock concert, so supersonic flight is banned over densely populated areas. NASA said the noise generated when the X-59 passes overhead is about 75 decibels, quieter than the sound of a car door closing 6 meters away.
◇ Dispersing shock waves with an arrowhead nose to reduce noise
X-59 development proceeded under NASA's Quiet SuperSonic Technology (QueSST) program. Skunk Works, the advanced aircraft development unit of U.S. defense contractor Lockheed Martin, led the effort. The name dates to 1943, when Lockheed Martin secretly developed the P-80 Shooting Star fighter and its researchers worked in a large tent next to a rubber factory with a strong sulfur odor. The formal name of Skunk Works is Advanced Development Programs (ADP).
A total of $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 is its unique design. The first thing that stands out is the long, slender nose. Unlike other jets, the nose accounts for one-third of the 30-meter fuselage. The nose was made narrow and long to disperse, not compress, shock waves. The problem is the view. The cockpit sits low inside the arrowhead-like fuselage, leaving no forward visibility.
NASA and Lockheed Martin, instead of direct vision, put a forward-facing display in the cockpit window. Two cameras capture the outside for this purpose. A camera on the forward canard is used to detect hazards ahead, and a camera under the fuselage provides the images needed for landing. Of course, if the cameras go dark, small windows on both sides of the cockpit allow for some visibility.
To increase commercial viability, the X-59 did not separately develop materials or an engine. For example, the engine is the one used in the JAS 39 Gripen, Sweden's 4.5-generation multirole fighter. Instead, unlike other supersonic jets, the engine was mounted on top of the wing rather than underneath. That also helped reduce the sonic boom. With the engine above the wing, the shock waves generated there travel upward rather than down toward the ground.
◇ Aiming for twice the speed and altitude of existing 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 entered a stable test rhythm with 16 flights over the past 90 days."
NASA's ultimate goal is for the X-59 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 existing airliners. At sea level, that would be 1,960 kph. If it currently takes about eight hours to fly from London to New York, the X-59, if it evolves into a quiet Concorde, could cut that to four hours.
So far, 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. Built by the Soviet design bureau Tupolev, it was the world's first supersonic airliner and succeeded in its maiden flight on Dec. 31, 1968. But due to safety issues, it flew only 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/