Radioisotope Thermoelectric Generator

Power source · 1961

Year: 1961
Kind: Power source
Materials: Plutonium-238 oxide, silicon-germanium or lead-telluride thermocouples, an iridium cladding.
Efficiency: 5–7 %.
Used In: Voyager, Cassini, New Horizons, the Mars rovers.
Power Density: A few watts per kilogram, falling as the plutonium decays.
Cycle: None

How It Works

A lump of plutonium-238 gets hot from its own decay; thermocouples across the temperature difference make a small steady current for decades. No moving parts, no sunlight needed — the power supply for wherever solar panels cannot go.

Equations

Thermoelectric Figure of Merit Half-Life Seebeck Effect Radioactive Decay Law

Elements

Silicon Germanium Tellurium Iridium Plutonium

Referenced by

element

Germanium Iridium Plutonium Silicon Tellurium

equation

Half-Life Radioactive Decay Law Seebeck Effect Thermoelectric Figure of Merit

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From the Machines database in Notion, last edited 2026-08-16. This page is the row, rendered by the build; nothing on it is written by hand.