Rugged, scramjet inlet temperature and velocity sensor: Design and ground test

The design and testing of a gas temperature and velocity scramjet engine inlet sensor based on tunable diode laser absorption spectroscopy of oxygen is discussed. The robustness and stability of the optical design necessitated by the dynamic vibrational and thermal environment were balanced against the need for compact size and very high signalto-noise ratio in a low-pressure, high-altitude flight regime. Test results demonstrated very good mechanical and thermal stability and an adequate signal-to-noise ratio for altitudes up to 30 km with predictedO₂ absorbance peaks greater than the signal standard deviation by a factor of more than 3.