Gassler, Carter D. and Durka, Michael J. and Herzog, Natan P. and Barry, Matthew M.
(2025)
Efficient Computational Method for Three-Dimensional Thermally- and Electrically-Coupled Performance Prediction of GPHS-RTG.
Proceedings of Nuclear and Emerging Technologies for Space (NETS 2025).
pp. 256-263.
Abstract
This paper introduces a novel analytic model for thermally and electrically coupled General Purpose Heat Source–Radioisotope Thermoelectric Generators (GPHS-RTGs). The model simplifies the RTG’s complex structure by leveraging symmetry arguments, capturing critical radiative, conductive, and electrical interactions while significantly reducing computational costs. The model includes many segmented unicouples and multi-foil insulation (MFI) sections, which enable it to assess spatial variations in thermal and electrical performance. Results demonstrate that unicouples closer to the RTG’s midspan heat source support exhibit approximately 1\% higher power output than those near the end caps due to radiation view factor disparities. Scaling up the model to a full RTG configuration, the total predicted beginning-of-mission (BOM) electrical power output is 295.5 W, aligning well with the 296 W average reported for the Cassini mission’s RTGs. The model reveals that MFI layers limit heat loss to only 0.1\% of the total heat from the GPHS, ensuring thermal efficiency. The surface temperatures of the GPHS bricks range between 1,310.6 K and 1,311.6 K, with a nearly uniform MFI surface temperature from 1,307.3 K to 1,307.9 K. This framework also provides granular insights into unicouple performance: unicouples on the diagonal relative to the GPHS produce less power due to unfavorable radiation view factors, resulting in slight asymmetries across the RTG’s electrical output. The model’s ability to resolve unicouple-level behavior while maintaining RTG-wide thermal and electrical balances makes it a powerful tool for analyzing RTG configurations.
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