Absorption-Based Laser Mass Flow Meter for Iodine-Fed Electric Propulsion: Design and Experiments

In electric propulsion for space applications, searching for alternative propellants is increasingly important due to limited resources and economic considerations. Among the candidates, iodine has emerged as promising thanks to its favorable chemical and physical properties for propulsion and its lower cost and simpler storage compared with xenon. However, its corrosive behavior is a drawback, as iodine reacts with many aerospace materials, and its condensable nature prevents using propellant management systems like those for noble gases. At the University of Pisa, activities on fluidics for iodine-fed electric propulsion systems and material compatibility studies led to the development of a mass flowmeter within the “iFACT-MP” Horizon EU project. The device is a spectrophotometric flow meter measuring instantaneous mass flow through a cell in series with the iodine feeding line, upstream of a thermal throttle. A beam splitter directs part of the light to a reference photodiode to compensate for laser intensity variations. Temperature and absorption measurements allow inferring iodine pressure in the cell, while the thermal throttle ensures sonic conditions, enabling correlation with instantaneous mass flow. The mass flow meter shows good behavior and repeatability, especially at low mass flow rates.