A Status Update on the eMMRTG Project

Abstract

NASA has employed Radioisotope Thermoelectric Generators (RTGs)to power many missions throughout the past several decades. The Multi-Mission RTG (MMRTG)used on Mars Science Laboratory is the most recent generator developed, and the only spaceflight-qualified system currently available. The enhanced Multi-Mission RTG (eMMRTG)would be an upgrade of the MMRTG using the most current thermoelectric (TE)technology, and would provide the space community with a system that would have substantially higher end-of-design-life (EODL)power. The NASA RPS Program recently instantiated an eMMRTG system development project, evolving from an ongoing technology maturation effort at JPL to a project designed to mature and transition the skutterudite (SKD)TE couples and technology into an operational RTG. The project has made significant advances in maturing SKD technology for use in the eMMRTG, and is looking ahead to potential RTG system development. Mini-module and couple life tests have produced substantial performance data that has helped refine the couple design and support lifetime performance predictions. Additional strength and thermoelectric properties tests have been performed to verify the design specifications and robustness of the candidate TE couples. Replacing the current MMRTG couples with SKD also necessitates system design changes that must be well understood. Recent systems engineering studies have focused on minimizing risk associated with updating the flight-proven MMRTG design. Upgrading the module insulation has been shown to result in 98% lower levels of CH4/H2 outgassing products. Performance analysis has been completed using the most recent TE couple sizes in order to understand the maximum acceptable power degradation rate to achieve the required eMMRTG power of 77 W at EODL. This paper provides an update on recent SKD technology maturation efforts and the results of several systems engineering tasks that continue to pave the way for successful system development.