NASA has pushed back the first flight of the X-59 low-boom supersonic demonstrator to 2024 after a series of subsystem issues encountered during check-out tests at Lockheed Martin’s Skunk Works facility in Palmdale, California, late this summer proved harder to solve than expected.

“We want to fly as early as possible, but we want to fly safely,” says the agency, which—together with Lockheed Martin—has been troubleshooting a variety of drop-out and safety system redundancy problems across several subsystems.

First reported in August, the issues are related to the flight-control computer and hydraulic system and were encountered during structural coupling tests at Palmdale. The coupling tests were designed to evaluate the interaction between the airframe and the flight-control system, and to ensure freedom from any aeroelastic and aeroservoelastic instabilities. 

Developed by Lockheed for NASA’s Quiet Supersonic Technology program, the almost 100-ft.-long X-59 was originally due to fly in 2021. However, the latest systems-related delays add to a series of hold-ups which have included workforce hiring issues, the pandemic and technical challenges related to wiring and final systems integration. Up until recently the agency still hoped to make the first X-59 flight by year-end with a transition shortly after to the nearby NASA Armstrong Flight Research Center at Edwards AFB, for follow-on envelope expansion.

Commenting on the delay, NASA says: “This one-of-a-kind experimental aircraft requires unique, complex engineering, and its team encountered several technical challenges over the past year. The X-59 is currently in the integrated testing phase, which must be completed to help ensure safe, successful flights. NASA plans to release a more specific timeline for first flight when the flight readiness review is completed, following integrated testing.”

The X-59 has been designed to collect community-response data on the public acceptability of reduced sonic booms. The data will be used by U.S. and international authorities to determine whether a boom standard can be set that will enable lifting of the prohibition on civil supersonic flight over land which has been in place since the 1970s.

However, to achieve low-intensity booms at the X-59’s design speed of Mach 1.4, the aircraft is configured with a sharply swept delta wing and extended cantilevered nose section which makes up more than one-third of the vehicle’s length. Specifically designed with stiffness for high-speed testing, rather than strength for payload capability, the long, slender shape therefore poses significant aeroelastic challenges.