Temperature Measurement of HEK-X Expansion Tube Flow by Laser Absorption Spectroscopy

An expansion tube is a promising facility to simulate atmospheric entry conditions, although its fl ow conditions have not been completely characterized mainly owing to its short operation time. In this study, laser absorption spectroscopy was applied to diagnose HEK-X expansion tube fl ow in the Kakuda Space Center. The target is an absorption line of an oxygen molecule at 763nm. To increase the sensitivity, optical path length was extended by fi ve times using mirrors. Con-sequently, an absorption pro fi le with a fractional absorption of 2.4 « 0.3% was detected at a shock velocity of 7.65 « 0.05km / s. The estimated translational temperature from the Voigt fi tting was 2750 « 450K.