A short document summarizes the redesign of a xenon-ion spacecraft thruster to increase its operational lifetime beyond a limit heretofore imposed by nonuniform ion-impact erosion of an accelerator electrode grid. A peak in the ion current density on the centerline of the thruster causes increased erosion in the center of the grid. The ion-current density in the NSTAR thruster that was the subject of this investigation was characterized by peak-to-average ratio of 2:1 and a peak-to-edge ratio of greater than 10:1. The redesign was directed toward distributing the same beam current more evenly over the entire grid and involved several modifications of the magnetic-field topography in the thruster to obtain more nearly uniform ionization. The net result of the redesign was to reduce the peak ion current density by nearly a factor of two, thereby halving the peak erosion rate and doubling the life of the thruster. (Note: NSTAR stands for NASA SEP Technology Application Readiness; SEP stands for solar electric propulsion.)

This work was done by Dan Goebel, James Polk, Anita Sengupta, and Richard Wirz of Caltech for NASA's Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Innovative Technology Assets Management
JPL
Mail Stop 202-233
4800 Oak Grove Drive
Pasadena, CA 91109-8099
(818) 354-2240
E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-43495.

Topics:
Data management Documentation Erosion Mechanical Components Mechanics Spacecraft Spacecraft Sun and solar Vehicles Vehicles
This Brief includes a Technical Support Package (TSP).
Document cover
Increasing the Life of a Xenon-Ion Spacecraft Thruster

(reference NPO-43495) is currently available for download from the TSP library.

Don't have an account?

Magazine cover
NASA Tech Briefs Magazine

This article first appeared in the November, 2007 issue of NASA Tech Briefs Magazine (Vol. 31 No. 11).

Read more articles from the archives here.

Overview

The document titled "Increasing the Life of a Xenon-Ion Spacecraft Thruster" (NPO-43495) outlines a significant advancement in xenon ion thruster technology developed by NASA's Jet Propulsion Laboratory. The primary focus of this innovation is to address the life-limiting issue of grid erosion, which occurs at the maximum ion current density location in traditional ion thrusters, such as the NASA NSTAR thruster.

Xenon ion thrusters are crucial for spacecraft propulsion, but their lifespan is often restricted due to excessive erosion of the grids, particularly in the peak current density region. The existing NASA NSTAR ion thruster experiences a peak-to-average ion current density ratio of 2:1 and a peak-to-edge ratio exceeding 10:1, leading to high erosion rates at the center of the thruster. This erosion limits the throughput to less than 200 kg, which is a significant constraint for long-duration space missions.

The innovative solution presented in this document involves generating an extremely flat plasma profile within the thruster. This uniformity in the plasma profile allows for consistent erosion across the grids, effectively doubling the thruster's life while maintaining the same beam current and thrust levels. The key strategies employed to achieve this include:

  1. Optimizing Magnetic Field Design: This enhances radial ion confinement and increases plasma density near the grid's edge, which helps in achieving a more uniform ionization process.

  2. Even-Numbered Ring Cusp Design: The design features an optimum length-to-diameter ratio that demagnetizes electrons from the on-axis cathode, promoting uniform ionization throughout the thruster.

  3. Magnetic Shim Utilization: A magnetic shim is placed on the inside diameter of the magnet ring at the accelerator, significantly reducing radial magnetic field penetration, which contributes to the flat plasma profile.

As a result of these innovations, the new thruster design achieves a peak-to-average ion current density ratio of 1.08, compared to the previous 2:1 ratio. This advancement effectively cuts the peak erosion rate in half, thereby extending the operational life of the thruster.

Overall, this document highlights a promising development in ion thruster technology that could enhance the efficiency and longevity of spacecraft propulsion systems, facilitating more ambitious space exploration missions.