The NASA Glenn Research Center has been supporting development of a Stirling Radioisotope Generator (SRG) by the Department of Energy (DOE), with Lockheed Martin Civil Space Systems (Valley Forge, PA) as the system integrator under contract to the DOE. The generator will utilize free-piston Stirling power-conversion technology to produce electrical power from a plutonium-238 heat source and will be capable of operation in deep space or in gaseous atmospheres such as on Mars. The first generator version was designed to produce 110 W from two Infinia Corp. convertors and was titled SRG110. The project has been redirected to increase efficiency and specific power by using Advanced Stirling Convertors (ASCs) from Sunpower, Inc. After this redirection, the generator title was changed to Advanced Stirling Radioisotope Generator (ASRG). Both Stirling power convertor designs make use of noncontacting, moving parts to eliminate wear mechanisms and enable long life.
Glenn has been supporting Lockheed Martin and the ASRG project by providing key data in the areas of performance enhancement and risk mitigation. Glenn tasks include extended-duration convertor testing, heater head life assessment, structural dynamics testing and analysis, organics assessment, and reliability analysis.
The purpose of extended testing is to provide independent validation and verification of the conversion technology as well as to demonstrate life and reliability. To accomplish this, several convertors have been put on extended, around-the-clock operation. The Stirling research lab at Glenn comprises six test stands for in-air operation and one for thermal vacuum operation. Each test stand can maintain a pair of convertors in unattended mode. Five of the stands can sample the convertor working fluid via a residual gas analyzer and ultra-high-vacuum system. The gas analysis capability allows for the detection of contaminants entering the convertor working fluid, either through pressure vessel flange o-rings or by outgassing of internal components. Three pairs of flight-prototype convertors, known as Technology Demonstration Convertors (TDCs), have accumulated over 92,000 hr total of operation with no failures. These units, manufactured by Infinia Corp. are prototypes of the units intended for integration into the SRG110. TDCs #13 and #14 have accumulated 24,000 hr of operation, and TDCs #15 and #16 have accumulated 10,000 hr. TDCs #5 and #6 were set up in a thermal vacuum environment to simulate operation in deepspace and have accumulated over 10,000 hr.
Test setup of TDCs #15 and #16.
TDCs #5 and #6 configured for thermal vacuum extended operation.
Preparations have been made to begin extended operation of six Sunpower, Inc., ASC convertors in air and thermal vacuum environments. The ASC testing will support Lockheed Martin’s development of the ASRG. This effort is supported by NASA’s Science Mission Directorate, Radioisotope Power Systems.
| TDC Pair |
Extended operation time, hr |
|---|---|
| #13 and #14 | 24,000 |
| #15 and #16 | 10,000 |
| #5 and #6 | 10,016 |
Find out more about the research of Glenn’s Thermal Energy Conversion Branch: http://www.grc.nasa.gov/WWW/TECB/
Glenn contact: Jeffrey G. Schreiber, 216-433-6144, Jeffrey.G.Schreiber@nasa.govLast updated: October 19, 2007
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