Absorption-based Laser Mass Flow Meter for Iodine Feeding System for Electric Propulsion

Iodine came up recently as a feasible alternative to xenon and krypton to be used in space electric propulsion applications. Iodine presents good ionization properties and a high atomic mass, which allow it to yield a good propulsive performance. Iodine is stored in a solid state, allowing to achieve higher storage densities, useful in volume-constrained applications. Nevertheless, the condensible nature and the reactivity of iodine prevents the use of propellant management systems and components used in noble gas-based systems. The University of Pisa is developing an iodine feeding system for electric propulsion applications, which controls the mass flow rate through the thermal control of the sublimation process and a thermal throttle. The article presents the main results of an ongoing activity aimed at the development of a laser-based mass flow meter to be used in the feeding system. The device measures the light absorbance of the iodine flow in a region upstream of the thermal throttle. Upon an integral-measurement calibration procedure, the spectrophotometric device allows to infer the mass flow rate instantaneous value. The measurement procedure and the underlying theory are described, as well as the calibration methodology and experimental setup.