Radioisotope thermoelectric generator
A Radioisotope thermoelectric generator, or RTG, is a form of electrical generator, that relies on the heat generated from decaying elements, such as Plutonium, to power a device approximating a human lifetime, or longer. They were first concieved by Soviet scientists. RTGs are useful in situations where solar cells are impractical, such as deep space, and conventional sources uneconomical. As of 2011, there are 301 scientific RTGs in active service, with 12 in space. There are more, undisclosed amounts in military service. It is believed that the vast majority of Soviet RTGs have decayed to the point of obsolescence, but some, are still believed to be generating power.
Mechanisms behind the RTG
The RTG utilizes decaying atoms of unstable elements, to generate electricity. The decay process releases heat, over long periods of time. Using the thermoelectric effect, usable quantities of electricity can be generated. The specific device used, is the Thermoelectric couples.