Multi-Hundred-Watt radioisotope thermoelectric generator

Assembled from 18 blocks · 2 evidence · 28 related

1. Story
2. The power source that has kept both Voyagers alive for forty-nine years. Each spacecraft carries three Multi-Hundred-Watt units on a boom; each unit holds spheres of plutonium-238 dioxide whose radioactive decay produces heat, and a bank of silicon-germanium thermocouples turns part of that heat directly into electricity with no moving parts. Together they supplied about 470 watts at launch. Output has fallen ever since, by roughly four watts a year, for two compounding reasons: the plutonium decays with an 87.7-year half-life, and the thermocouples themselves degrade. That decline is the whole operational story of the mission after 1989. It cannot be repaired, it cannot be paused, and it is predictable to the watt — which is why the flight team can plan instrument shutdowns years ahead and argue about them in terms of watts rather than science priorities alone. Not a place.
3. Knowledge
4. Multi-Hundred-Watt radioisotope thermoelectric generator
5. Plutonium-238
6. Connections
7. Voyager 1
8. Voyager 2
9. Plutonium-238
10. Voyager 1 launches
11. Voyager 1's cosmic ray subsystem is switched off
12. Voyager 2's low-energy charged particle instrument is switched off
13. Voyager 1's low-energy charged particle instrument due for shutdown
14. The "Big Bang" power manoeuvre on Voyager 2
15. Multi-Hundred-Watt radioisotope thermoelectric generator
16. Evidence
17. Voyager 1's cosmic ray subsystem was switched off on 25 February 2025 and Voyager 2's low-energy charged particle instrument on 24 March 2025; both spacecraft lose about four watts of generator output per year; three science instruments continued to operate on each; Voyager 1's low-energy charged particle instrument was to run through 2025 and be switched off in 2026, and Voyager 2's cosmic ray subsystem was scheduled for shutdown in 2026, with the plan expected to keep at least one instrument running on each spacecraft into the 2030s. V55 verification basis: the release was not fetched — jpl.nasa.gov and science.nasa.gov are both blocked by this session's network egress proxy — but search results carried these specific figures and dates and attributed them to this release.
18. Each Voyager carries three Multi-Hundred-Watt radioisotope thermoelectric generators fuelled with plutonium-238 dioxide and using silicon-germanium thermocouples, supplying roughly 470 watts at launch and declining by about four watts a year through fuel decay (half-life about 87.7 years) and thermocouple degradation. V55 verification basis: THE PAGES WERE NOT REACHED and only the four-watt annual decline is independently supported, by the March 2025 JPL release. The generator count, launch power, thermocouple material and half-life come from general knowledge and require confirmation.