Title

Lithium Purification System Development for Long-Life Lithium-Fed Lorentz Force Accelerators

Abstract

Lithium is an attractive metal propellant for advanced nuclear-electric propulsion missions because its low molecular weight results in high Isp and high conductivity for advanced MPD thrusters. The ALFA2 NASA program investigated a liquid lithium MPD thruster to support a > 5 year mission. Unfortunately, lithium is corrosive to most metals, leeches elements from alloys, destroys dielectric insulators, and is prone to contamination. Therefore, long-duration deep space missions using lithium will only be possible if these adverse effects can be mitigated or eliminated. For the ALFA2 NASA mission, cathode erosion and work function poisoning due to impurities (notably oxygen) was observed and severely limits lifetime. Using a lithium purification and filtration system with highly porous gettering materials in series with cold trap filters is a possible way of reducing lithium contamination levels; thereby improving thruster lifetime. A proof-of-concept experiment was carried out to examine cold filtering and evaluate several candidate getter materials for purification. The long-term goal is to develop an active filtering and purification system for the ALFA2 thruster, or other lithium/liquid metal fed thrusters, to mitigate contamination effects for long-duration (>5 years) space missions. Starfire Industries successfully demonstrated: (1) reduction in impurity content by filtration, (2) regeneration of the filter assembly, (3) getter operation and regeneration, and (4) established a baseline for designing a prototype for a laboratory-scale thruster. These advances increase the regenerable filtration and gettering concept from TRL 1 to TRL 3. In addition, significant mass reduction is realized when compared to getter-only purification schemes that would likely perform poorer than the described system.

Department(s)

Mechanical and Aerospace Engineering

Sponsor(s)

NASA Small Business Innovation Research

Keywords and Phrases

Cathode Erosion; Nuclear-Electric Propulsion

Library of Congress Subject Headings

Lithium

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2007 American Institute of Aeronautics and Astronautics (AIAA), All rights reserved.


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