Development of Integrated Control and Diagnostics Architecture for an Iodine Feeding System for Electric Propulsion

Xenon has generally been the propellant of choice for spacecraft electric propulsion systems but, recently, due to its higher storage density, lower cost and comparable performance, iodine has gained attention as a valid alternative, especially in volumeconstrained applications. However, because of its high reactivity, iodine imposes requirements on material-compatibility, preventing the use of propellant management systems typically used with noble gas-based systems. The University of Pisa is currently developing an iodine feeding system for generating a controlled iodine vapor flow, for use as a propellant in plasma propulsion systems, such as Hall or gridded ion thrusters. The architecture of the feeding system consists of several subassemblies that allow to generate and regulate the flow of iodine using only thermal controllers. The feeding system is composed by a PTFE tank, a sublimation body, which heats up and regulates the temperature at which iodine vapour is generated, an on-off valve, a laser-based mass flow meter, which measures the light absorbance of the iodine flow allowing to infer the instantaneous mass flow rate, and a thermal throttle, which allows to perform a fine mass flow rate control. Two prototypes of this type of iodine feeding system have been built and underwent extensive characterization campaigns. As part of the development of the iodine propellant management technologies, a third improved prototype is currently under development considering form factors within the CubeSat Standard. Within this improvement, the development of an integrated management and control electronic system has been proposed. The system makes use of Arduino microcontroller boards to manage and perform the different control and diagnostics functions, as well as to communicate with the external computer (either laboratory or spacecraft on-board computer). Besides the thermal regulation of the different components, the system controls the activation of the valve, the control and acquisition of the mass flow meter data, as well as failure detection and system health monitoring. The present article presents the propellant management systems developed at UniPi, details the mass flowmeter architecture and presents preliminary results from the experimental characterization of the system in a rough vacuum environment.