Three RTG units, electrically parallel-connected, are the central power sources for the mission module. Each RTG is made up of a radioisotope heat source, a thermoelectric converter, a gas pressure venting system, temperature transducers, connectors, a heat rejecting cylindrical container, and bracketry. The RTGs are mounted in tandem (end-to-end) on a deployable boom as part of the MM.
The heat source radioisotopic fuel is Plutonium-238 in the form of the oxide Pu02. In the isotopic decay process, alpha particles are released which bombard the inner surface of the container. The energy released is converted to heat and is the source of heat to the thermoelectric converter.