IN-SITU MEASUREMENT OF HYDROCHLORIC-ACID IN ROCKET EXHAUST CLOUDS USING A REMOTELY PILOTED AIRCRAFT

An instrumentation system employing an RPV (remotely piloted vehicle) platform was developed for temporally and spatially resolved air pollu tion measurements, and was used to measure the evolution of gas-phase HCl in exhaust clouds from a solid rocket motor firing and fuel pit bu rns. A thermistor and a sensitive (ppmv-level), rapid-response <0.1 se c) infrared absorption sensor for HCl were mounted in a flow channel i n the RPV, permitting concentration and temperature measurements to be made in the cloud on a several-meter scale. The RPV system was flown in a series of field tests at Thiokol Corporation's Elkton, MD divisio n to evaluate the HCl content of the exhaust products of a new Mg-base d fuel formulation. Measurements were made in the clouds from Al-based and Mg-based solid fuel pit burns and a Mg-fueled motor firing over p eriods of several minutes. Elevated temperatures and HCl concentration s were found to be temporally correlated with video images of the part iculate cloud. Cl originating from the ammonium perchlorate oxidizer a ppeared in the exhaust as HCl in each of the tests. Both the macroscop ic and local cloud parameters indicate that the Mg-based fuel may prov ide some reduction in HCl concentration compared to the standard Al-ba sed fuel.