Ultrasonic measurements of burning rates in full-size rocket motors

A new ultrasonic sounding technique to measure the instantaneous propellant thickness in a solid rocket motor has been developed and was used successfully in the static firing tests with full-size motors. The technique applies a low-frequency ultrasonic wave (50 or 100 kHz) [1, 2]. Sets of transducers were installed in the motor case using magnets, with each set comprising a transmitter/receiver and receivers. Transducer installation required careful setup to maintain good acoustic coupling between each transducer and motor case and to withstand the harsh vibrations of the environment. Time histories were obtained for the propellant thickness at various locations during the burning tests. This paper presents in detail the ultrasonic sounding and installation techniques and the results obtained