A recent article in Invention & Technology magazine about the Pioneer 10 spacecraft mentions it’s RTG power units. I have never found an adequate explanation of just how these devices function. The heat given off by the decay of plutonium is converted into electricity by thermocouples, but what does this mean exactly? I can understand a heat souce boiling water and using the steam to spin a turbine, but how can “just heat” be converted into electricity that the electronics aboard a spacecraft can use with no moving parts like turbines and generators.
Pioneer 10 has been functioning for almost 30 years! The RTG units seem like a very practical small source of power, why are they not used in any other venue except spacecraft? Radiation dangers?