• mass flow meter
• Hall Thruster
• alternative propellants
• iodine
• propellant management
• spectrophotometry
• Bayesian inference

In Hall thrusters a propellant is ionized and the positive ions are accelerated outside electrostatically by means of a local electric field established in a plasma. This is done by using a transverse magnetic field which can reduce the electron conductivity. This kind of technology is employed to perform satellite attitude control, station keeping and eventually deep space exploration. Currently, Hall Thrusters, as well as most state-of-the-art electric propulsion systems, are designed to operate running on xenon because of the good propulsive performance it is possible to attain with it. However, xenon is rather rare and therefore its price tends to fluctuate. Moreover, high-pressure storage conditions are required for noble gases in general, thus the application of this propulsion system to smaller satellites is limited. To circumvent the issues associated with xenon, research activities are carried out nowadays with the aim of finding new propellants to be used in space electric propulsion. In this context, iodine has been revealed to feature several properties which make it capable of yielding good propulsive performance. Nevertheless, the condensible nature and the reactivity of iodine prevents the use of propellant management systems and components used in noble gas-based systems. In this framework, the University of Pisa is currently developing different prototypes of iodine feeding systems for electric propulsion applications. The process of development and characterization of an iodine feeding system requires methods to measure the mass flow rate of vaporized iodine delivered by the reservoir. So far, the average mass flow rate has been carefully characterized, but there are not experimental results available concerning the short-term behavior of the system. The reason for this is that no mass flow meters are available which are chemically compatible with iodine and capable of operating exposed to high vacuum environment.
The present dissertation is aimed at the theoretical and experimental studies of an absorption-based laser mass flow meter which will enhance the qualification process of iodine-fed propulsion systems. A description of the architectures of both the iodine feeding system and the mass flow meter is provided. A 1-D thermal fluid model is developed to discuss the effects of the geometry of the mass flow meter on the uncertainty of the output measured variable. The experimental activities are carried out with the aim of performing a calibration of the instrument in vacuum environment. The data obtained in the various experimental campaigns have been analyzed both in the frequentist approach and in the Bayesian framework. Moreover, the equivalence between the two methods was proved with the implementation of a uniform prior distribution.