Testing to Characterize the Advanced Stirling Radioisotope Generator Engineering Unit

Abstract

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 ...

Advanced Stirling Convertor (ASC-E2) Characterization Testing

“…These numbers are similiar to the numbers from the AC bus voltage variation test conducted with the ASRG EU, which had a hot-end temperature sensitivity of -73 to -81 C/V and a piston amplitude senstivity of 0.23 to 0.30 mm/V (Ref. 4). The difference between the operating points may account for some of the differences in the two sets of numbers.…”

Terrestrial applications of extreme environment stirling space power systems

“…A second concept demonstration engine was developed that is a hybrid configuration of a thermo-acoustic and free-piston Stirling engine. It was developed using similar technology as is currently used in the Advanced Stirling Radioisotope Generator (ASRG) [3], but it is designed to prevent the displacer from moving through the hot-end region of the engine. It also achieved over 30% efficiency with a hot-end temperature of 650°C and cold-end temperature of 30°C at 96 Hz (see Fig.…”

U.S. Space Radioisotope Power Systems and Applications: Past, Present and Future

“…A cold gas is passed over the EU to maintain proper thermal operating conditions. The EU is planned to demonstrate 14,000 hours of operation in validating the design's viability for flight on a NASA science mission (Lewandowski and Schreiber, 2010). The EU has achieved over 11,000 hours (April, 2011) with a prototypical flight controller.…”