Numerical studies were conducted on a small ion engine system called μ1, which was developed for micro-spacecraft propulsion. For its miniaturized application, the μ1 ion engine is very small in size and its beam current and propellant utilization efficiency are lower than those of standard-sized ion engines. As it operates in a low perveance range with a molybdenum two-grid system, the acceleration grid experiences very severe erosion, and the extraction ion beam performance degrades substantially because of the scattering of highly diverted ions and neutrals and the impact of backstreaming charge exchange ions. In this study, the decrease in the propellant utilization efficiency and the lifetime of the μ1 ion engine were firstly assessed using the JIEDI tool, considering the effect of the change in extraction ion beam performance. Lifetime analysis showed that the μ1 grid system can operate over its required lifetime of 10000 h, however, the propellant utilization efficiency decreased significantly from 0.42 at the beginning of life to 0.30 at the grid structural failure of 27000 h. The agreement of grid erosion patterns after the first 150-h of operation between the simulation and the experiment supports the validity of the analysis. In addition to the lifetime assessment, the grid parameters were parametrically searched to achieve both high propulsion performance and long life. One of the strategies is to double the diameters of the screen and accelerator grid holes as well as the accelerator grid thickness, keeping the separation distance between the screen and accelerator grids unchanged.
2014 The Japan Society for Aeronautical and Space Sciences