The Advanced Stirling Radioisotope Generator (ASRG), a high efficiency generator, is being considered for space missions. Lockheed Martin designed and fabricated an engineering unit (EU), the ASRG EU, under contract to the Department of Energy. This unit is currently undergoing extended operation testing at the NASA Glenn Research Center to generate performance data and validate life and reliability predictions for the generator and the Stirling convertors. It has also undergone performance tests to characterize generator operation while varying control parameters and system inputs. This paper summarizes and explains test results in the context of designing operating strategies for the generator during a space mission and notes expected differences between the EU performance and future generators.I. Introduction HE Advanced Stirling Radioisotope Generator (ASRG) continues flight development towards potential use on space missions. A key step in this process was the desi gn and fabrication of an ASRG en gineering Lunt (EU), by system integrator Lockheed Martin Space Systems Company (LM) under contract to the Department of Energy.' The generator assembly was completed in December 2007 and controller integration followed in March 2008. This Lunt underwent a series of system-level tests to qualification level thermal and dynamic environments at LM. These included thermal balance, thermal performance, mechanical disturbance, sine transient. random vibration, simulated pyrotechnic shock. and electromagnetic interference.' Following an internal inspection, LM delivered the ASRG EU to the NASA Glenn Research Center (GRC) on August 28, 2008, for extended operation. The EU underwent inspection followed by integration into a test facility specially designed for it. The ASRG EU began extended operation on November 6, 2008. This test is intended to demonstrate extended operation of an integrated system and to provide additional data from long-tern operation of Stirling convertors. The EU has operated over 11,000 hours to date at NASA GRC.The ASRG EU is the first Stirling generator system tested at GRC that has an integrated heat source, insulation. sealed housing, and controller. Figure 1 shows a cutaway model of the ASRG EU. The EU contains two Advanced Stirling Convertors (ASC-Es) secured together with an interconnect sleeve. An electric heat source (EHS), held against each ASC-E heat collector, provides the heat input. The cold-side adapter flanges (CSAFs) conduct heat rejected from the convertors through the beryllium housing and fins for radiation in a vacuum environment or convection to air. Argon fills the housing, sealed using o-rings and gaskets. A gas management valve allows access to the argon. A pressure relief device (PRD) is provided to vent the argon during launch as the surrounding air pressure approaches the vacuum of space, improving effectiveness of the insulation surrounding the heat source. The controller is mounted to the outside of the housing. Connectors on the end enclosures, housing, and controller ...

Significant progress was made developing the Advanced Stirling Radioisotope Generator (ASRG), a 140-watt radioisotope power system. While the ASRG flight development project has ended, the hardware that was designed and built under the project is continuing to be tested to support future Stirling-based power system development. NASA GRC recently completed the assembly of the ASRG Engineering Unit 2 (EU2). The ASRG EU2 consists of the first pair of Sunpower's ASC-E3 Stirling convertors mounted in an aluminum housing, and Lockheed Martin's Engineering Development Unit (EDU) 4 controller (a fourth generation controller). The ASC-E3 convertors and Generator Housing Assembly (GHA) closely match the intended ASRG Qualification Unit flight design. A series of tests were conducted to characterize the EU2, its controller, and the convertors in the flight-like GHA. The GHA contained an argon cover gas for these tests. The tests included: measurement of convertor, controller, and generator performance and efficiency, quantification of control authority of the controller, disturbance force measurement with varying piston phase and piston amplitude, and measurement of the effect of spacecraft DC bus voltage on EU2 performance. The results of these tests are discussed and summarized, providing a basic understanding of EU2 characteristics and the performance and capability of the EDU 4 controller. Nomenclature FA, FB= Total dynamic force for ASC A, ASC B (N); sum of piston and displacer inertial forces FD

No abstract

No abstract

100 We class Stirling convertors began extended operation testing at NASA Glenn Research Center (GRC) in 2003 with a pair of Technology Demonstration Convertors (TDCs) operating in air. Currently, the number of convertors on extended operation test has grown to 12, including both TDCs and Advanced Stirling Convertors (ASCs) operating both in air and in thermal vacuum. Additional convertors and an electrically heated radioisotope generator will be put on test in the near future. This testing has provided data to support life and reliability estimates and the quality improvements and design changes that have been made to the convertor.The convertors operated 24/7 at the nominal amplitude and power levels. Performance data were recorded on an hourly basis. Techniques to monitor the convertors for change in internal operation included gas analysis, vibration measurements and acoustic emission measurements. This data provided a baseline for future comparison. This paper summarizes the results of over 145,000 hours of TDC testing and 40,000 hours of ASC testing and discusses trends in the data. Data shows the importance of improved materials, hermetic sealing, and quality processes in maintaining convertor performance over long life.