The goal of this work was the setup of an electric propulsion (EP) sputtering test section as a feasibility study for ground-based sputter testing of spacecraft materials with a radio-frequency ion thruster (RIT). Such experiments deliver valuable data which are scarce but highly desired to model EP-based space missions, for example with SPIS (Spacecraft Plasma Interaction System), in order to predict the performance and lifetime of spacecraft components. This study assessed if sufficient testing conditions can be met to produce reliable experimental material data in the future. Therefore, the thruster was operated at ion energies of 1.5 keV and 1.8 keV, and a quartz crystal microbalance (QCM) was installed to detect sputter deposition rates. Molybdenum (Mo) and silver (Ag) were chosen as sputter targets. Wafer substrates served as a passive sampling method to characterize the composition of sputtered material by Rutherford Backscattering Spectrometry (RBS). Additionally, sputtering simulations matching the experimental conditions were conducted with the software SDTrimSP. We obtained comparable experimental and computational data, as measured sputter deposition rates lie within the simulated order of magnitude and to some extent show the predicted angular dependence. Analysis of deposited sputter material revealed the formation of metal oxides which requires a future adaption of the material specific QCM settings. Furthermore, the cooling system of the QCM sensor head was not sufficient, limiting the comparability of results.

A number of propellant/thruster combinations are under development in recent years that aim to replace the prevailing hydrazine-driven reaction control thrusters with less hazardous substances (“green propellants”). With some of these systems already in orbit, characterizing their contamination potential in a space environment becomes relevant. In this paper we discuss experiments on plume induced contamination from a novel propene/nitrous oxide bipropellant thruster, including high-speed imaging, SEM-EDS analysis, QCM measurements and in-situ mass spectrometry. Additional measurements of combustion chamber pressure complement the overall characterization of the thruster performance in a high vacuum environment. The main findings of this exploratory study are strong indications of solid and liquid phase particles being ejected from the nozzle, which will be investigated in a subsequent phase of the activity.

The induced contamination from two hydrazine-propelled thrusters is studied in the high-vacuum plume test facility for chemical thrusters at DLR Göttingen, STG-CT. A number of representative material samples are exposed to the freely expanding pulsed thruster plume for subsequent in-depth analysis at JPL. The plume gas is monitored in-situ with a mass spectrometer and quartz crystal microbalances, while non-gaseous ejecta are recorded with a high-speed camera setup. With the detailed chemical analysis ongoing we report on the measurements obtained during the campaign and immediate post-test observations.