English: Diagram of the Multihundred-Watt Radioisotope Thermoelectric Generator (RTG) units included on the spacecrafts Voyager 1 and Voyager 2. In this diagram of the RTG, the shell and the heat-to-electricity conversion couplings are displayed.
(The Inner Heat Source Unit is generating about 2400 Watts of thermal power at launch time - which is the decay heat of the containing plutonium-238 oxide. It is surrounded by 312 silicon-germanium (SiGe) thermoelectric couples, which are used to produce about 470 watts of electric power (at launch time), the remainder being dissipated as waste heat over the cooling-ribs or -fins)