NASA adds two retired F-15s to support X-59 quiet‑supersonic testing

NASA has incorporated a pair of former Air Force F-15 fighters into its Armstrong Flight Research Center fleet to strengthen support for the X-59 low‑boom program. One airframe will be upgraded with mission systems and sensors to serve as a dedicated research and chase platform while the second will provide parts to keep the fleet serviceable. These additions were handed over in December 2025 and are timed to sustain the X-59’s upcoming flight campaign phases. The X-59’s test regime operates at stratospheric altitudes, with the demonstrator cruising near 55,000 feet; modified F-15 capability to operate roughly 60,000 feet will allow closer, higher-fidelity measurements. NASA plans to employ the fighters for sensor carriage, high-speed visual documentation and Schlieren photography techniques that reveal pressure disturbances in the air column behind the demonstrator. That instrumentation suite, combined with close-proximity observation, addresses gaps in remote sensing where wake and shock details are most sensitive to geometry and atmospheric layering. Operationally, having an in-house chase asset reduces reliance on external contractor aircraft and simplifies logistics for long-duration test sequences over sparsely populated test ranges. From an engineering standpoint, the decision balances cost and capability: retrofitting an existing high-altitude jet is faster and cheaper than certifying a new platform for chase duties. For policy and commercialization prospects, improved empirical data from these flights will feed the noise models regulators use to consider lifting preexisting bans on supersonic overland operations. However, converting a fighter to a research role carries integration challenges — avionics coupling, data latency, and electromagnetic compatibility tests must be resolved before routine deployment. Longer term, sustained chase capability and parts availability could accelerate the X-59 program’s timeline for delivering definitive community-response data on perceived noise. If the collected evidence supports lower-than-expected annoyance levels, aerospace manufacturers will gain a clearer path to productizing low‑boom transport. For now, the F-15 additions are a pragmatic, near-term investment in flight-test infrastructure that tightens measurement fidelity and lowers operational risk for critical phases of the X-59 campaign.