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Lunar Surface Stirling Power Systems Using Isotope Heat SourcesFor many years, NASA has used the decay of plutonium-238 (Pu-238) (in the form of the General Purpose Heat Source (GPHS)) as a heat source for Radioisotope Thermoelectric Generators (RTGs), which have provided electrical power for many NASA missions. While RTGs have an impressive reliability record for the missions in which they have been used, their relatively low thermal to electric conversion efficiency and the scarcity of plutonium-238 (Pu-238) has led NASA to consider other power conversion technologies. NASA is considering returning both robotic and human missions to the lunar surface and, because of the long lunar nights (14.75 Earth days), isotope power systems are an attractive candidate to generate electrical power. NASA is currently developing the Advanced Stirling Radioisotope Generator (ASRG) as a candidate higher efficiency power system that produces greater than 160 W with two GPHS modules at the beginning of life (BOL) (~32% efficiency). The ASRG uses the same Pu-238 GPHS modules, which are used in RTG, but by coupling them to a Stirling convertor provides a four-fold reduction in the number of GPHS modules. This study considers the use of americium-241 (Am-241) as a substitute for the Pu-238 in Stirling- convertor-based Radioisotope Power Systems (RPS) for power levels from tens of watts to 5 kWe. The Am-241 is used as a substitute for the Pu-238 in GPHS modules. Depending on power level, different Stirling heat input and removal systems are modeled. It was found that substituting Am-241 GPHS modules into the ASRG reduces power output by about one-fifth while maintaining approximately the same system mass. In order to obtain the nominal 160 W of electrical output of the Pu-238 ASRG requires 10 Am-241 GPHS modules. Higher power systems require changing from conductive coupling heat input and removal from the Stirling convertor to either pumped loops or heat pipes. Liquid metal pumped loops are considered as the primary heat transportation on the hot end and water pumped loop/heat pipe radiator is considered for the heat rejection side for power levels above 1 kWe.
Document ID
Acquisition Source
Glenn Research Center
Document Type
Conference Paper
Schmitz, Paul C.
(Power Computing Solutions, Inc. Avon, OH, United States)
Penswick, L. Barry
(Sest, Inc. Middleburgh Heights, OH, United States)
Shaltens, Richard K.
(NASA Glenn Research Center Cleveland, OH, United States)
Date Acquired
August 24, 2013
Publication Date
July 1, 2010
Subject Category
Mechanical Engineering
Report/Patent Number
AIAA Paper 2009-4578
Meeting Information
Meeting: Seventh International Energy Conversion Engineering Conference (IECEC)
Location: Denver, CO
Country: United States
Start Date: August 2, 2009
End Date: August 5, 2009
Sponsors: American Inst. of Aeronautics and Astronautics
Funding Number(s)
WBS: WBS 138494.04.01.01
Distribution Limits
Public Use Permitted.
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