Historical RTG performance data through 2023

Radioisotope thermoelectric generators (RTG) are the only technology currently available that can provide reliable and consistent electrical power for decades while isolated in extreme environments. RTGs have been, and will continue to be, a critical enabling component in some of humankind's most impressive feats of space exploration in the past (e.g. Cassini), present (e.g. Voyager), and future (e.g. Dragonfly). Power produced by an RTG will slowly decrease over time due to decay of the radioisotope fuel and degradation of the materials within the generator. With over 60 years of history, the technology of RTGs has evolved from producing only a few electrical watts (e.g. SNAP-3B ~3 W) to nearing a kilowatt of total mission power (e.g. Cassini beginning-of-mission 887 W). They also evolved from systems that were only designed to last a few years into systems that are now exploring interstellar space 46 years after launch. Obviously, understanding how the performance of these systems changes over their lifetime is of very high interest to anyone planning a future space exploration mission. This dataset presents all of the power and performance information that is available for all spaceborne RTGs that have been flown by NASA and the US Department of Defense through mid-to-late 2023. Some performance data that has not previously been published is also provided here, including the full lifetime for Galileo and Pioneer 11, as well as a near complete lifetime for Pioneer 10. While all of the available performance data for RTGs is presented here, it should be noted that the context of each mission and RTG design is extremely important in understanding RTG behavior. It is not possible to provide enough context to fully appreciate the behavior of all 29 RTG space missions in a dataset publication, so users are highly encouraged to find the appropriate context in Chapter 8 of the book, The Technology of Discovery: Radioisotope Thermoelectric Generators and Thermoelectric Technologies for Space Exploration (ISBN: 9781119811367).

Methods
UPDATE STATUS: Active missions (except for Voyager) have been updated through mid-to-late 2023.

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Power values were collected from reputable and authoritative sources and organized into a tabular format of time versus normalized power. Normalized power is the power at a given time, divided by the power at the beginning-of-mission (BOM). BOM power for each mission is also provided. Because RTGs can take days to weeks to fully equilibrate with their environment, BOM power is defined here as the maximum RTG power produced over the first 30 days of the mission. For many missions, this will be the first data point.  Other missions (e.g. Curiosity) will reach this maximum power level after several days.

BOM for RTG missions does not have a consistent definition. For deep space or orbital missions, BOM is launch. For missions where the RTG was installed on the surface of an extraterrestrial body, BOM is either the landing date (e.g. Martian landers or rovers) or the date the RTG was installed (e.g. Apollo lunar missions).

Some important pieces of context for each RTG mission are also provided above the table.

Pedigree of the performance data for each mission in this dataset:

SNAP-9A (Transit 5BN-1 and Tranist 5BN-2), SNAP-19B (Nimbus III), SNAP-19 (Viking 1 and Viking 2), SNAP-27 (Apollo), and Transit-RTG were obtained from graphs presented in G.L. Bennett, J.L. Lombardo, and B.L. Rock, “US Radioisotope Thermoelectric Generators in Space,” Nucl. Eng., 25(2), 49–58 (1984).

SNAP-19 (Pioneer 10 and 11) was obtained from an internal memo published by Teledyne Energy Systems, Inc. (courtesy T. Hammel). Teledyne was the design and engineering agency in charge of the SNAP-19.

MHW-RTG (LES 8 and 9) were obtained from the Cassini Final Technical Report (DOE/SF/18852-T97) published by Lockheed Martin. Lockheed was the prime contractor and system integrator for all silicon germanium RTGs (i.e. MHW-RTG and GPHS-RTG) at that time.

MHW-RTG (Voyager 1 and 2) telemetry was obtained courtesy of E. Medina of the Jet Propulsion Laboratory. Due to recent issues with the Voyager spacecraft, a public data drop of Voyager telemetry has not occurred in a while. As a result, Voyager 1 and 2 data only go to August 2021.

GPHS-RTG (Galileo) telemetry was obtained courtesy of R. Gershman of the Jet Propulsion Laboratory.

GPHS-RTG (Ulysses) was obtained courtesy of the Mission Operations Manager N. Angold.

GPHS-RTG (Cassini) performance data was obtained directly from mission control at the Jet Propulsion Laboratory.

GPHS-RTG (New Horizons) telemetry was obtained courtesy of C. Hersman of the Applied Physics Laboratory.

MMRTG (Curiosity and Perseverance) telemetry was obtained courtesy of E. Clarke and L. Rich of the Idaho National Laboratory, as well as S. Bux and S. Pinkowski of the Jet Propulsion Laboratory.

放射性同位素热电发生器（Radioisotope Thermoelectric Generators, RTG）是目前唯一可在极端孤立环境中，长期稳定提供可靠电力的技术。长期以来，RTG都是、也将持续成为人类多项标志性太空探索壮举的关键支撑组件——从过往的卡西尼号（Cassini）、当前的旅行者号（Voyager），到未来的蜻蜓号（Dragonfly）均是如此。

由于放射性同位素燃料的衰变以及发生器内部材料的老化劣化，RTG的输出功率会随时间缓慢下降。历经60余年的发展，RTG技术已从仅能输出数瓦电力（如SNAP-3B约3瓦），演进至可提供近千瓦级的任务总功率（如卡西尼号任务初始功率为887瓦）；其设计寿命也从最初的数年，延长至如今可在发射46年后仍探索星际空间。显然，对于规划未来太空探索任务的人员而言，掌握这类系统全生命周期的性能变化规律具有极高的研究价值。

本数据集收录了截至2023年中后期，由美国国家航空航天局（NASA）与美国国防部（US Department of Defense）发射的所有星载RTG的全部可用功率与性能信息。此外，数据集还包含此前未公开的部分性能数据，例如伽利略号（Galileo）与先驱者11号（Pioneer 11）的完整全生命周期数据，以及先驱者10号（Pioneer 10）近乎完整的全生命周期数据。尽管本数据集收录了现有全部RTG性能数据，但需注意：各任务背景与RTG设计细节对于理解RTG运行行为至关重要。受限于数据集出版物的篇幅，无法为29项星载RTG太空任务逐一提供足够的背景信息以完整阐释其运行特性，因此强烈建议用户参考《探索技术：太空探索用放射性同位素热电发生器与热电技术》（ISBN: 9781119811367）一书的第8章获取相关背景。

方法
更新状态：截至2023年中后期，除旅行者号外的现役任务均已完成更新。

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功率数据均来自权威可信的来源，并整理为「时间-归一化功率」的表格格式。归一化功率指特定时间点的功率除以任务初始功率（beginning-of-mission, BOM）。各任务的任务初始功率亦已提供。由于RTG需要数天至数周才能与环境完全达到热平衡，本数据集将任务初始功率定义为任务首30天内RTG输出的最大功率。对于多数任务而言，该值即为首个数据点；而部分任务（如好奇号（Curiosity））则需经过数天才能达到该最大功率水平。

RTG任务的任务初始功率并无统一定义：对于深空或轨道任务，任务初始功率指发射时刻；对于将RTG安装在地外天体表面的任务，任务初始功率则指着陆时刻（如火星着陆器或火星车）或RTG安装时刻（如阿波罗（Apollo）月球任务）。

表格上方亦提供了各RTG任务的部分重要背景信息。

本数据集各任务性能数据的来源如下：
SNAP-9A（用于Transit 5BN-1与Transit 5BN-2）、SNAP-19B（用于Nimbus III）、SNAP-19（用于海盗1号与海盗2号）、SNAP-27（用于阿波罗任务）与Transit-RTG的数据均来自G.L. Bennett、J.L. Lombardo与B.L. Rock发表于《Nucl. Eng., 25(2), 49–58 (1984)》的论文《US Radioisotope Thermoelectric Generators in Space》中的图表。
SNAP-19（用于先驱者10号与先驱者11号）的数据来自Teledyne能源系统公司的内部备忘录（由T. Hammel提供），该公司曾负责SNAP-19的设计与工程工作。
MHW-RTG（用于LES 8与9）的数据来自洛克希德·马丁公司发布的《卡西尼最终技术报告（DOE/SF/18852-T97）》，该公司当时是所有硅锗RTG（即MHW-RTG与GPHS-RTG）的总承包商与系统集成商。
旅行者1号与旅行者2号的MHW-RTG遥测数据由喷气推进实验室的E. Medina提供。由于近期旅行者号航天器出现相关问题，其遥测数据的公开更新已有较长时间未进行，因此旅行者1号与2号的数据仅更新至2021年8月。
伽利略号的GPHS-RTG遥测数据由喷气推进实验室的R. Gershman提供。
尤利西斯号（Ulysses）的GPHS-RTG数据由任务运营经理N. Angold提供。
卡西尼号的GPHS-RTG性能数据直接来自喷气推进实验室的任务控制中心。
新视野号（New Horizons）的GPHS-RTG遥测数据由应用物理实验室的C. Hersman提供。
好奇号与毅力号（Perseverance）的MMRTG遥测数据由爱达荷国家实验室的E. Clarke、L. Rich，以及喷气推进实验室的S. Bux与S. Pinkowski提供。