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ABSTRACTThe room temperature ionic liquid propellant, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMI-Im) is being tested for the NASA DRS-ST7 mission. A capillary thruster configuration is planned for ST7, and time-of-flight experiments have shown that the spray of EMI-Im produces a mixture of primarily droplets and low levels of ions, resulting in a low specific impulse. Recently, pure ion emission was achieved for EMIIm in a wetted needle thruster, suggesting that this propellant, which has passed all spaceenvironmental exposure tests, may also be a candidate for high specific impulse missions. The use of wetted tips raises the question whether electrochemistry at the liquid-metal interface causes significant propellant fouling that will ultimately result in performance degradation due to the significantly longer propellant metal interaction times in comparison with the capillary design and the higher flow rates. Electrochemical fouling can be mitigated through a polarity alternation approach, which adds complexity to the power processing unit.' 15. SUBJECT