Advanced Stirling Convertor Durability Testing: Plans and Interim Results

Abstract

The U.S. Department of Energy (DOE), Lockheed Martin Corporation (LM), and NASA Glenn Research Center (GRC) have been developing the Advanced Stirling Radioisotope Generator (ASRG) for use as a power system for space science missions. In support of this program, GRC has been involved in testing Stirling convertors, including the Advanced Stirling Convertor (ASC), for use in the ASRG. This testing includes electromagnetic interference/compatibility (EMI/EMC), structural dynamics, advanced materials, organics, and unattended extended operation. The purpose of the durability tests is to experimentally demonstrate the margins in the ASC design. Due to the high value of the hardware, previous ASC tests focused on establishing baseline performance of the convertors within the nominal operating conditions. The durability tests present the first planned extension of the operating conditions into regions beyond those intended to meet the product spec, where the possibility exists of lateral contact, overstroke, or over-temperature events. These tests are not intended to cause damage that would shorten the life of the convertors, so they can transition into extended operation at the conclusion of the tests. This paper describes the four tests included in the durability test sequence: 1) start/stop cycling, 2) exposure to constant acceleration in the lateral and axial directions, 3) random vibration at increased piston amplitude to induce contact events, and 4) overstroke testing to simulate potential failures during processing or during the mission life where contact events could occur. The paper also summarizes the analysis and simulation used to predict the results of each of these tests. Nomenclature IntroductionThe Thermal Energy Conversion Branch at NASA Glenn Research Center (GRC) has been supporting the development of the Advanced Stirling Radioisotope Generator (ASRG). The ASRG has been identified for potential use on two of the three candidate Discovery 12 missions (Ref. 1). A key element of the ASRG project is providing life, reliability, and performance data for the Advanced Stirling Convertor (ASC). For this purpose, GRC has established a laboratory that is conducting extended operation of several ASCs (Ref. 2). The goal of this effort is to generate performance data over a sufficiently long period of time (tens of thousands of hours) to support probabilistic reliability analyses.Due to the high value of the hardware, ongoing activity at GRC focuses on operation of hermeticallysealed ASCs at nominal operating conditions. The hermetic nature of those convertors makes inspection difficult. The convertors for the durability test feature a removable pressure vessel to allow for partial disassembly of the convertors and inspection of internal components. The purpose of the durability tests is to experimentally demonstrate the margins in the ASC design. The durability tests present the first planned extension of the operating conditions into regions beyond those intended to meet the ASC product specificatio...

Dynamic Power Convertor Development for Radioisotope Power Systems at NASA Glenn Research Center

“…A static acceleration exposure was also performed on an ASC in the 2012 timeframe (Ref. 24). The lab has cultivated a performance tracking methodology to support this long-term operation analysis, one in which the test article parameters are constantly recorded.…”