Will this Thruster Get Us to Europa? Modeling Ion Engine Erosion and Quantifying Lifetime Margins and Uncertainty

Solar electric  propulsion  (EP) is a key technology for human and robotic space missions, and is part of NASA’s vision for  expanding  human presence beyond  low  earth  orbit.  The  high specific impulse but  at  the price of EP enables reductions in propellant mass, of long burn times. Deep space missions require operating times of many 104 hours. Demonstrating that the thruster meets this requirement is a challenge. Multiple life tests of the full  mission duration are  not practical. The  life capability  must  be demonstrated  by  combining physics‐based modeling and short duration testing.

JPL developed the CEX2D and CEX3D codes to model erosion of ion accelerator systems in ion engines, a dominant failure mechanism. The codes model a primary ion beamlet, and charge exchange (CEX) ions from the beamlet. Impingement of main, beamlet, and CEX ions on the grids then determine erosion rates. The models  predict time‐to‐failure, but  key questions include: What is the uncertainty in those estimates? How much margin is needed to account for the uncertainties? Estimating uncertainty in experiments is routine, but the modeling community is still developing techniques for estimating errors. In this talk we discuss the physical processes of ion engine grid erosion, how they are modeled, and methods for quantifying model uncertainty and required life margins.