Iridium catalyst detection by laser induced breakdown spectroscopy

Monopropellant catalytic thrusters have been used for decades in space systems due to their simplicity and reliability. However, the degradation or loss of the catalyst is a major lifetime limiting effect, both for hydrazine fueled systems as well as for newer hydrazine-replacement fueled systems. Currently there is no in-situ diagnostic technique to measure the health status of the catalyst in such devices. Herein, we report a gas-phase diagnostic technique for measuring iridium, a common catalyst material for monopropellant thrusters. Laser induced breakdown spectroscopy was employed to quantify iridium in the gas phase by thermally vaporizing various organometallic iridium compounds to known concentrations within a test cell and observing the resulting iridium optical emission lines that had no interfering lines in the region from other possible emitting species (such as nitrogen, oxygen, and carbon). A limit of detection for the iridium was determined to be 6.21 μmol/L (197 ppm by volume), and this, to our knowledge, is the first report on the quantitative analysis of gas-phase iridium by laser induced breakdown spectroscopy.