Subsonic in-flight temperature and pressure measurements using a scramjet inlet flow sensor

The performance of a scramjet inlet sensor based on tunable diode laser absorption spectroscopy of oxygen in the Aband near 760 nm during a low-altitude, subsonic flight test is discussed. Though the scramjet did not reach the targeted hypersonic flight regime due to the malfunction of the first-stage booster, analysis of the spectral absorption data acquired during the descent flight below 3 kmsuccessfully determined pressure and temperature in the inlet and demonstrated that the system was capable of producing an adequate signal-to-noise ratio to allow temperature, pressure, and velocity measurements under the expected hypersonic flight conditions at altitudes up to at least 30 km. This is the first flight-tested tunable diode laser sensor for a scramjet inlet flow, and the robustness and stability of the sensor design in dynamic load conditions were made evident by the quality of the data recorded after a very unstable and high-g launch scenario.