NASA GRC Support of the Flight ASRG Project

Wilson, Scott D.; Wong, Wayne A.

doi:10.2514/6.2014-3859

Cited by 3 publications

(5 citation statements)

References 7 publications

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“…technology, but the ASRG program was later canceled due to budget constraints, leaving the MMRTG as the currently available option (Wilson & Wong, 2014). Considering the US is planned to only produce an estimated 1.5 kg of Pu-238 per year, there would not be enough plutonium to meet the projected demands for the next decade unless production is increased significantly.…”

Section: Overview Of Problem and Its Significancementioning

confidence: 99%

“…shown that even the latest RTG models have not been able to achieve conversion efficiencies much above six percent (p. 8), but NASA has been working on creating an Advanced Stirling Radioisotope Generator (ASRG) with The U.S. Department of Energy and Lockheed Martin in hopes to achieve efficiencies on the order of four times that (Wilson & Wong, 2014). The ASRG was designed to utilize the higher efficiency Stirling cycle by obtaining work from heat-driven pistons rather than TECs, but the program had to be terminated in 2013 for budget reasons (Wilson & Wong, 2014). Despite termination, NASA has still continued research but as of 2015 a flight ready model may not be ready until as late as 2030 due to long-term testing that needs to be completed, whereas an eMMRTG flight system is estimated to be ready by 2022 (Lee & Bairstow, 2015).…”

Section: Lessons From Prior Responses To the Problemmentioning

confidence: 99%

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Enhancing NASA's Multi-Mission Radioisotope Thermoelectric Generator Using Highly Efficient Thermoelectric Materials

Houtmann¹

2020

M:TURJ

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This project proposal aims to enhance NASA’s Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) by identifying and analyzing new material technologies that have been researched for their excellent thermoelectric properties at higher temperatures. By choosing the most efficient thermoelectric material available, the MMRTG’s energy conversion efficiency will be greatly improved as thermoelectric generator efficiencies are largely determined by the properties of the materials within the thermocouple devices used to convert the heat into energy. A project that focuses on enhancing the MMRTG is imperative for the future of space exploration as there is global shortage of plutonium fuel production, limiting future missions to available supplies. A more efficient generator will minimize the use of this fuel while maximizing power output, allowing for increased mission capabilities and better conservation of the scarce plutonium fuel. In this report, lanthanum telluride, Yb14MnSb14, and a multiple-filled skutterudite (SKD) compound are analyzed for their excellent thermoelectric performance. The multiple filled SKD compound is chosen as the ideal material to enhance the MMRTG based on the low cost and low risks associated with the material while producing a nearly identical efficiency relative to the other candidates. Keywords: eMMRTG, MMRTG, thermoelectric materials, thermoelectric generator, efficiency

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Section: Overview Of Problem and Its Significancementioning

confidence: 99%

Section: Lessons From Prior Responses To the Problemmentioning

confidence: 99%

Enhancing NASA's Multi-Mission Radioisotope Thermoelectric Generator Using Highly Efficient Thermoelectric Materials

Houtmann¹

2020

M:TURJ

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“…Accelerated life testing can be, and has been performed, at the component level (Ref. 19). Hot-end materials can be subjected to higher temperature and stress than the convertor operating design point.…”

Section: Path To Flightmentioning

confidence: 99%

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

Oriti

Wilson

2018

2018 International Energy Conversion Engineering Conference

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The Thermal Energy Conversion Branch at NASA Glenn Research Center is supporting the development of high-efficiency power convertors for use in radioisotope power systems (RPS). Significant progress was made toward such a system that utilized Stirling conversion during the 2001 to 2015 timeframe. Flight development of the Advanced Stirling Radioisotope Generator (ASRG) was canceled in 2013 by the U.S. Department of Energy (DOE) and NASA Headquarters primarily due to budget constraints, and the Advanced Stirling Convertor (ASC) technology contract was subsequently concluded in 2015. A new chapter of technology development has recently been initiated by the NASA RPS Program. This effort is considering all dynamic power convertor options, such as Stirling and Brayton cycles. Four convertor development contracts supporting this effort were awarded in 2017. The awarded contracts include two free-piston Stirling, one thermoacoustic Stirling, and one turbo-Brayton design. The technology development contracts each consist of up to three phases: design, fabrication, and test. As of May 2018, all contracts have completed the design phase, and each underwent a design review with an independent review board. Three of the contracts are planned to execute the phase 2 option for fabrication. Convertors manifesting from these development efforts will then undergo independent validation and verification (IV and V) at NASA facilities, which will consist of convertor performance and RPS viability demonstrations. Example tests include launch vibration simulation, performance mapping over the environmental temperature range, and static acceleration exposure. In parallel with this renewed development effort, Glenn is still demonstrating free-piston Stirling convertor technology using assets from previous projects. The Stirling Research Laboratory (SRL) is still operating several convertors from previous development projects, which have similarities and relevance to current contract designs. Four of these are flexure-bearing based and another six are gas bearing based. One of the flexure-bearing convertors has accumulated over 110,000 h of operation and holds the current record for maintenance-free heat-engine run time. Another flexure-bearing convertor was recently manually shut down after 105,620 h of operation, then disassembled and inspected. This inspection produced a wealth of information about the effects of this amount of run time on the technology's components. One of the engineering unit flexure-bearing convertors recently underwent a launch simulation vibration test, a static acceleration exposure up to 20 g, and was then placed on extended operation. Among the gas-bearing convertors, the longest running unit has accumulated over 70,000 h of operation. Four high-fidelity gas-bearing convertors from the ASRG project are still operating continuously for which the longest run time has reached 28,000 h.

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“…Stirling cycle applications include cryo-coolers 9,10 , natural gas co-generation units 11,12,13 , solar-dynamic power conversion 14, 15,16 , and nuclear dynamic power conversion 17,18,19,20,21 . They are typically used in applications which have high fuel costs or in systems that require closed-cycle operation.…”

Section: Introductionmentioning

confidence: 99%

“…High efficiency and closed-cycle operation are both requirements of space power systems, making free-piston Stirling engines candidates for these applications. They are a key technology in NASA's Radioisotope Power System program because their high efficiency potentially enables NASA to increase the number of missions it can fly over the coming decades using the limited supply of plutonium-238 20,21,22 . They also trade favorably in low to moderate power level fission power applications because their high efficiency requires less heat input from the reactor and reduces heat rejection requirements, reducing the mass of the reactor shield and the radiators 17,18,19,23 .…”

Section: Introductionmentioning

confidence: 99%

Improving Power Density of Free-Piston Stirling Engines

Briggs

Prahl

Loparo

2016

14th International Energy Conversion Engineering Conference

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Analyses and experiments demonstrate the potential benefits of optimizing piston and displacer motion in a free-piston Stirling Engine. Isothermal analysis shows the theoretical limits of power density improvement due to ideal motion in ideal Stirling engines. More realistic models based on nodal analysis show that ideal piston and displacer waveforms are not optimal, often producing less power than engines that use sinusoidal piston and displacer motion. Constrained optimization using nodal analysis predicts that Stirling engine power density can be increased by as much as 58% using optimized higher harmonic piston and displacer motion. An experiment is conducted in which an engine designed for sinusoidal motion is forced to operate with both second and third harmonics, resulting in a piston power increase of as much as 14%. Analytical predictions are compared to experimental data and show close agreement with indirect thermodynamic power calculations, but poor agreement with direct electrical power measurements.

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NASA GRC Support of the Flight ASRG Project

Cited by 3 publications

References 7 publications

Enhancing NASA's Multi-Mission Radioisotope Thermoelectric Generator Using Highly Efficient Thermoelectric Materials

Enhancing NASA's Multi-Mission Radioisotope Thermoelectric Generator Using Highly Efficient Thermoelectric Materials

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

Improving Power Density of Free-Piston Stirling Engines

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