Gridded Ion Thruster Mission Life Prediction through Reduced Order Modeling

High power electric propulsion space missions require vacuum facility ground tests to predict in-space life and performance. Gridded ion thruster (GIT) mission life prediction must account for facility effects such as facility induced neutral and sputterant flux, which affect thruster performance and grid erosion, which can obfuscate predictions of grid transparency and electron backstreaming. This work demonstrates a simple GIT Predictive Engineer Model (GIT PEM) that captures these coupled effects. The model uses experimental and computational data from NASA’s NSTAR thruster, though any GIT could be used. The GIT PEM is exercised for key aleatoric and epistemic uncertainties, including those related to life threshold, model estimations, relevant physics, thruster operating conditions, and mission scenarios to characterize model sensitivities and uncertainty quantification. Results show that different life mechanisms dominate depending on imposed assumptions, examined factors, and uncertainties. For example, the most common life mechanism for ion thrusters, electron backstreaming, can exhibit high uncertainty for simplified approximations and is strongly influenced by facility-related uncertainties such as charge exchange collisions and sputter deposition.