Advanced Stirling Radioisotope Generator: Design Processes, Reliability Analyses Impacts, and Extended Operation Tests

Ha, Chuong T.; Fernández, Roque B.; Cornford, Steven L.; Feather, Martin S.

doi:10.1063/1.2845003

Cited by 3 publications

(2 citation statements)

References 4 publications

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“…Despite the promised high power, a mechanical system may not have the longevity for deep space missions . [28][29][30][31][32][33][34][35][36] Figure 1. Comparison of conventional semiconductor-based thermoelectric concept (a) to the new metallic junction thermoelectric concept (b).…”

Section: Introductionmentioning

confidence: 99%

Metallic junction thermoelectric device simulations

Duzik

Choi

2017

SPIE Proceedings

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Thermoelectric junctions made of semiconductors have existed in radioisotope thermoelectric generators (RTG) for deep space missions, but are currently being adapted for terrestrial energy harvesting. Unfortunately, these devices are inefficient, operating at only 7% efficiency. This low efficiency has driven efforts to make high-figure-of-merit thermoelectric devices, which require a high electrical conductivity but a low thermal conductivity, a combination that is difficult to achieve. Lowered thermal conductivity has increased efficiency, but at the cost of power output.An alternative setup is to use metallic junctions rather than semiconductors as thermoelectric devices. Metals have orders of magnitude more electrons and electronic conductivities higher than semiconductors, but thermal conductivity is higher as well. To evaluate the viability of metallic junction thermoelectrics, a two dimensional heat transfer MATLAB simulation was constructed to calculate efficiency and power output. High Seebeck coefficient alloys, Chromel (90%Ni-10%Cr) and Constantan (55%Cu-45%Ni), produced efficiencies of around 20-30%. Parameters such as the number of layers of junctions, lateral junction density, and junction sizes for both series-and parallel-connected junctions were explored.

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Section: Introductionmentioning

confidence: 99%

Metallic junction thermoelectric device simulations

Duzik

Choi

2017

SPIE Proceedings

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“…As the emphasis of this project has shifted to system integration, LMSSC has taken on the leadership for overall reliability, consistent with their role as the system integration contractor responsible for reliability of the integrated generator. 12 GRC and Sunpower continue to play key roles in the efforts coordinated through the ASRG Reliability Working Group. The intent is to mitigate risk and maximize reliability in meeting the 17 year life requirement for the ASRG.…”

Section: A Reliabilitymentioning

confidence: 99%

Supporting Technology at GRC to Mitigate Risk as Stirling Power Conversion Transitions to Flight

Schreiber

Thieme

Wong

2008

6th International Energy Conversion Engineering Conference (IECEC)

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Stirling power conversion technology has been reaching more advanced levels of maturity during its development for space power applications. The current effort is in support of the Advanced Stirling Radioisotope Generator (ASRG), which is being developed by the U.S. Department of Energy (DOE), Lockheed Martin Space Systems Company (LMSSC), Sunpower Inc., and the NASA Glenn Research Center (GRC). This generator would use two high-efficiency Advanced Stirling Convertors (ASCs) to convert thermal energy from a radioisotope heat source into electricity. Of paramount importance is the reliability of the power system and as a part of this, the Stirling power convertors. GRC has established a supporting technology effort with tasks in the areas of reliability, convertor testing, high-temperature materials, structures, advanced analysis, organics, and permanent magnets. The project utilizes the matrix system at GRC to make use of resident experts in each of the aforementioned fields. Each task is intended to reduce risk and enhance reliability of the convertor as this technology transitions toward flight status. This paper will provide an overview of each task, outline the recent efforts and accomplishments, and show how they mitigate risk and impact the reliability of the ASC's and ultimately, the ASRG. Nomenclature

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Extending time-series models for irregular observational gaps with a moving average structure for astronomical sequences

Ojeda

Palma

Eyheramendy

et al. 2023

RAS Techniques and Instruments

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In this study we introduce a novel moving-average model for analyzing stationary time series observed irregularly in time. The process is strictly stationary and ergodic under normality and weakly stationary when normality is not assumed. Maximum likelihood estimation can be efficiently carried out through a Kalman algorithm obtained from the state-space representation of the model. The Kalman algorithm has order O(n) (where n is the number of observations in the sequence), from which it is possible to efficiently generate parameter estimators, linear predictors and their mean squared errors. Two procedures were developed for assessing parameter estimation errors: one based on the Hessian of the likelihood function and another one based on the bootstrap method. The behavior of these estimators was assessed through Monte Carlo experiments. Both methods give accurate estimation performance, even with relatively small number of observations. Moreover, it is shown that for non-Gaussian data, specifically for the Student’s-t and Generalized error distributions, the parameters of the model can be estimated precisely by maximum likelihood. The proposed model is compared to the continuous autoregressive moving average models (CARMA), showing better performance when the moving average parameter is negative or close to one. We illustrate the implementation of the proposed model with light curves of variable stars from the OGLE and HIPPARCOS surveys and stochastic objects from ZTF. The results suggest that the iMA model is a suitable alternative for modeling astronomical light curves, particularly when they have negative autocorrelation.

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Advanced Stirling Radioisotope Generator: Design Processes, Reliability Analyses Impacts, and Extended Operation Tests

Cited by 3 publications

References 4 publications

Metallic junction thermoelectric device simulations

Metallic junction thermoelectric device simulations

Supporting Technology at GRC to Mitigate Risk as Stirling Power Conversion Transitions to Flight

Extending time-series models for irregular observational gaps with a moving average structure for astronomical sequences

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