Design and development of iodine flow control systems for miniaturized propulsion systems

Iodine becomes increasingly popular as alternative propellant for electric propulsion (EP) systems offering several advantages over established xenon. However, iodine is also a reactive and corrosive element. Thus, a careful material selection for the EP system itself, but also for components employed on the satellite is required in the light of typical space mission durations of several years. Here, we carefully define an approach for mimicking long-term interaction of material specimens with iodine in a space environment. The space conditions cover typical iodine atmospheres (10− 1 to 10− 4 Pa), which occur in the vicinity of a satellite employing an iodine-fed EP system, and exposure times, which correspond to 10 years of mission duration. The approach is used to expose a wide range of metal specimens commonly used on spacecraft to iodine. Chemical modifications of the surfaces of the treated samples are analyzed by x-ray photoelectron spectroscopy (XPS). The elemental metals Fe, Ti, Al, and Nb chemically react with iodine, whereas the elemental metals Ni, Cr, Ta, W, and Mo are basically inert. The stainless-steel and aluminum metal alloys show the same behavior as the corresponding dominant elemental specimens, i.e., Fe and Al, respectively. Somewhat surprisingly, Cr as constituent in stainless steel reacts with iodine, in contrast to elemental Cr. Nevertheless, our studies reveal that long-term exposure to low-pressure iodine atmospheres is not critical for the macroscopic structural integrity of all tested specimens even over space mission durations of several years. The reaction with iodine is macroscopically a surface effect, which mainly affects the optical appearance.

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Corrosion of metal parts on satellites by iodine exposure in space

Zschätzsch

Benz

Holste

et al. 2022

J Electr Propuls

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Review on the current state of iodine compatible neutralizers

Becke,

Kottke,

Vaupel

et al. 2024

J Electr Propuls

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The rising deployment numbers of electric propulsion systems and the increased price of noble gas propellants have created the demand for alternative propellants. Iodine is a very promising candidate, which has already been successfully demonstrated with a variety of thruster types. The main challenge remains to design an iodine compatible neutralizer for those thruster types requiring neutralization. This review first gives an overview of the most common neutralizer principles and categorizes them according to their efficiency and current generation. Special consideration is given to plasma bridge hot cathodes, as they allow the broadest scaling of the supplied current levels. Different emitter types and materials are then discussed based on their resistance to iodine corrosion. In the final section, the experimental results of neutralizers tested with iodine are compared and the encountered difficulties are reviewed. A summary presents the best candidates, based on the maximum neutralization current and the technological readiness level. The recommended neutralizer technologies for ultra-low currents are filament cathodes, for low currents radio-frequency-cathodes and for high currents plasma bridge hot cathodes. Filament cathodes have already been flight proven in an iodine propulsion system and radio-frequency-cathodes have been tested successfully in a laboratory environment. While possible in theory, a successful long-term test of an iodine-fueled plasma bridge hot cathode has not been achieved so far.

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Analytical model of a Hall thruster

Lafleur,

Chabert

2024

Physics of Plasmas

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Hall thrusters are one of the most successful and prevalent electric propulsion systems for spacecraft in use today. However, they are also complex devices and their unique E×B configuration makes modeling of the underlying plasma discharge challenging. In this work, a steady-state model of a Hall thruster is developed and a complete analytical solution presented that is shown to be in reasonable agreement with experimental measurements. A characterization of the discharge shows that the peak plasma density and ionization rate nearly coincide and both occur upstream of the peak electric field. The peak locations also shift as the thruster operating conditions are varied. Three key similarity parameters emerge that govern the plasma discharge and which are connected via a thruster current–voltage relation: a normalized discharge current, a normalized discharge voltage, and an amalgamated parameter, α¯, that contains all system geometric and magnetic field information. For a given normalized discharge voltage, the similarity parameter α¯ must lie within a certain range to enable high thruster performance. When applied to a krypton thruster, the model shows that both the propellant mass flow rate and the magnetic field strength must be simultaneously adjusted to achieve similar efficiency to a xenon thruster (for the same thruster geometry, discharge voltage, and power level).

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Design and development of iodine flow control systems for miniaturized propulsion systems

Cited by 3 publications

References 9 publications

Corrosion of metal parts on satellites by iodine exposure in space

Corrosion of metal parts on satellites by iodine exposure in space

Review on the current state of iodine compatible neutralizers

Analytical model of a Hall thruster

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