Two-photon Absorption Laser Induced Florescence of Krypton Fueled Resistojet Thruster - Interactions with Ambient Neutrals*

Environmental effects during thruster testing result in discrepancies between laboratory performance and actual performance in space. Specifically, the buildup of ambient neutrals in the test chamber affects measurements of thruster performance. Testing conditions, such as operating pressure, also result in discrepancies in reported performance by different groups. Therefore, measurement of the distribution of ambient neutrals across a large range of operating pressures in the test chamber is required to fully assess thruster performance. Non-invasive, spatially localized neutral diagnostics for thruster test chambers are rare. Here, we use two-photon absorption laser-induced fluorescence (TALIF) to excite neutral ground-state krypton non-invasively. The spatially resolved neutral number density and velocity in the exhaust plume of a krypton-fueled resistojet thruster and chamber is presented and the effect of ambient pressure on thruster performance is investigated. Fluorescence is captured using an Andor iStar iCCD fast-gated camera. A novel image processing algorithm is used to derive exhaust plume velocities from raw image data. The novel algorithm decreases processing time of data by using a full dataset fitting method and the analysis time scales linearly with pixel count. We present TALIF measurements of the interaction between a krypton-fueled resistojet exhaust and neutrals. The novel image processing algorithm and how it compares to standard pixel by pixel approaches is also discussed.