Improving the Total Impulse Capability of the NSTAR Ion Thruster With Thick-Accelerator-Grid Ion Optics

Abstract

The results of performance tests with thick-accelerator-grid (TAG) ion optics are presented. TAG ion optics utilize a 50 % thicker accelerator grid to double ion optics ’ service life. NSTAR ion optics were also tested to provide a baseline performance for comparison. Impingement-limited total voltages for the TAG ion optics were only 0-15 V higher than those of the NSTAR ion optics. Electron backstreaming limits for the TAG ion optics were 3-9 V higher than those for the NSTAR optics due to the increased accelerator grid thickness for the TAG ion optics. Screen grid ion transparencies for the TAG ion optics were only about 2 % lower than those for the NSTAR optics, reflecting the lower physical screen grid open area fraction of the TAG ion optics. Accelerator currents for the TAG ion optics were 19-43 % greater than those for the NSTAR ion optics due, in part, to a sudden increase in accelerator current during TAG ion optics ’ performance tests for unknown reasons and to the lower-than-nominal accelerator aperture diameters. Beam divergence half-angles that enclosed 95 % of the total beam current and beam divergence thrust correction factors for the TAG ion optics were within 2º and 1%, respectively, of those for the NSTAR ion optics.