Stirling convertor extended operation testing and data analysis at GRC

Abstract

Extended operation of Stirling convertors is essential to the development of radioisotope power systems and their potential use for long-duration missions. To document the reliability of the convertors, regular monitoring and analysis of the extended operation data is particularly valuable, allowing us to better understand and quantify long-life characteristics of the convertors. Furthermore, investigation and comparison of the extended operation data to baseline performance data provides an opportunity to understand system behavior should any off-nominal performance occur. Glenn Research Center (GRC) has tested 16 Stirling convertors under 24-hour unattended extended operation, including four that have operated in a thermal vacuum environment and two that are operating in the Advanced Stirling Radioisotope Generator Engineering Unit. Ten of the sixteen convertors are the Advanced Stirling Convertors (ASC) developed by Sunpower, Inc. with GRC. These are highly efficient (conversion efficiency of up to 38% for the ASC-1), low-mass convertors that have evolved through technologically progressive convertor builds. Six convertors at GRC are Technology Demonstration Convertors from Infinia Corporation. They have achieved greater than 27% conversion efficiency and have accumulated over 185,000 of the total 265,000 hours of extended operation at GRC. This paper presents the extended operation testing and data analysis of free-piston Stirling convertors at NASA GRC as well as how these tests have contributed to the Stirling convertor's progression toward flight.