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The plug architecture replaces traditional solid exhaust plugs with an elongated design characterized by a hollow interior and a uniformly porous surface. By positioning the plug's crown inside the nozzle, the exhaust travels through a convergent passage up to the crown and a divergent passage past it. In standard solid plugs, shock waves become unsteady at off-design pressure ratios, causing severe acoustic resonance. The porous skin stabilizes localized flow separation and disrupts unsteady shock formation. By doing so, the technology alters complex aerodynamic interactions providing the noise reduction. Translation of the plug provides variable design condition without requiring heavy, maintenance-intensive mechanisms. Sub-scale acoustic testing demonstrates superior noise suppression without sacrificing aerodynamic efficiency. While existing aerodynamic treatments (such as tabs or boundary layer tripping) only mitigate screech or transonic tones, the porous plug represents a breakthrough by eliminating BBSN and EBBN as well as other aberrant noise. Additionally, thrust measurement data indicates this dramatic noise reduction is achieved with minimal impact on the gross thrust coefficient, preserving engine performance within <1% of conventional plugs. While NASA originally developed this porous plug nozzle to help next-generation commercial supersonic aircraft meet strict LTO noise regulations, the technology offers broader aerospace utility. The design can be implemented in high-speed military aircraft to mitigate operational acoustics, or integrated into aerospace inlets and internal ducts to suppress flow noise originating from center-bodies.

The disclosed technology provides a multistage system for evaluating the free-flight behavior of test articles across of the supersonic, transonic, and subsonic regimes. First, a drop platform is lifted to high altitudes using a lifting device, such as a stratospheric balloon. The drop platform houses multiple projectiles, each containing an ejection mechanism, an on-board avionics suit, and an instrumented test article. Upon reaching the target altitude via the lifting device, the drop platform releases the projectiles sequentially. Each projectile accelerates to a target speed and altitude before ejecting its test article into the freestream. The test articles, such as a scaled re-entry capsule, then collect flight data during their descent through the various Mach regimes, providing valuable insights into their flight performance under mission-relevant conditions. This innovative testing system offers several benefits. It enables the simultaneous testing of multiple vehicles, facilitating the evaluation of design variations as well as statistical analyses of vehicle behavior. This system also provides significant cost savings in comparison to other state-of-the-art testing methods, such as ballistic range testing. Additionally, the test articles within each projectile are easily interchangeable through a simple, modular change of a support surface in the ejection mechanism. This flexibility enables the system to accommodate a range of other aerodynamic technologies, including other vehicles, parachutes, propulsion systems, and defense technologies. This system can enhance the efficiency and robustness of reentry vehicle design, testing, and simulation operations through the collection of rich, flight-relevant data.