Abstract
Full-aperture ion optics simulations have been conducted for the inhomogeneous plasma source of a miniature ion propulsion system (MIPS) to design a high-efficiency accelerator grid that provides high degree of the neutral confinement and absence of direct ion impingement. The designed accelerator grid has flat upstream and smoothly curved downstream surfaces with straight holes for easy low-cost manufacture. The diameter of the accelerator aperture was changed from the nominal value of 0.40 mm to 0.25 mm, which decreased neutral leakage and increased the propellant utilization efficiency from 31 to 50%. The direct impingement of ions caused by decreasing the accelerator aperture diameter was compensated by reducing the thickness of the accelerator grid while taking into account the inhomogeneous ion beam current density profile of the MIPS. An off-design performance simulation was conducted to validate the proposed grid design; the obtained results showed that the ion beam could be accelerated smoothly even during throttling the beam current between 75 and 150%. A grid wear simulation was also performed to compare the changes in the propellant utilization efficiency between the nominal and high-efficiency grids caused by erosion. It was found that the propellant utilization efficiency of the high-efficiency grid was greater than that of the nominal grid within the first 5,000 h of operation and that its lifetime exceeded 10,000 h of the accumulated operation time. By using the proposed high-efficiency accelerator grid and MIPS plasma source, the propellant utilization efficiency was increased, while the accelerator impingement current became negligible.
Highlights
A gridded ion thruster is a form of electric propulsion that provides thrust by expelling high-speed ions electrostatically using a set of multi-aperture electrodes
Ion thrusters are employed in microspacecraft missions; for example, a miniature ion propulsion system (MIPS), which represented an electron cyclotron resonance (ECR) discharge ion thruster, was developed at the University of Tokyo and flight-tested in the PROCYON and Hodoyoshi-4 space missions.[5,6]
The propellant utilization efficiency and the specific impulse of the MIPS are equal to around 30% and 1,200 s, respectively, which are lower than those of the typical gridded ion thrusters
Summary
A gridded ion thruster is a form of electric propulsion that provides thrust by expelling high-speed ions electrostatically using a set of multi-aperture electrodes ( called grids). The propellant utilization efficiency (defined as the ratio of the ion beam flux to the total propellant mass flow) and the specific impulse of the MIPS are equal to around 30% and 1,200 s, respectively, which are lower than those of the typical gridded ion thrusters Both these parameters can be increased by improving the ion production performance in the discharge chamber and reducing the neutral leakage through the grid apertures. It causes severe sputtering and becomes a source of spacecraft contamination. Full-aperture ion optics and grid wear simulations were conducted to consider the highly inhomogeneous beam current and ion velocity distributions of the MIPS discharge plasma source
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