Each of the two Voyager craft gets its electrical power from a miniature nuclear generator, which consists of three metal cylinders, each 17in (430mm) long and 13in(330mm) wide, connected end to end. The cylinders are packed with plutonium dioxide, a radioactive substance.
Surrounding the core of each cylinders are hundreds of thermocouples. There are miniature electric circuits, consisting of a piece of silicon and a piece of germanium. One end of each thermocouple is heated by the decaying plutonium; the other faces outwards into the cold of space.
The difference in temperature between the two ends of the thermocouple causes an electrical current to flow through it. When electron in the silicon are distributed by heating, free electrons will tend to move to the germanium, creating a current.
When each Voyager was launched, in 1977, the three cylinders together produced 475 watts of electric power. But the power decreases by 7 watts per year, as the plutonium decays.
Picture Credit : Google
