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Radioisotope Thermoelectric Generators (RTGs) are highly reliable solid state devices that produce electricity through the flow of heat generated by the decay of a radioisotope, primarily plutonium-238, through a device called an unicouple. RTGs have been used for over thirty years to provide electrical energy to satellites and deep space probes. The three most recent deep space missions are being powered by the General Purpose Heat Source (GPHS) RTG, which utilizes 572 unicouples to produce 300 watts of electricity, nominal. Each of these unicouples has a C-seal, which is designed to prevent air from entering the interior of the RTG. This is necessary because oxygen degrades the performance of the unicouples and the multi-foil insulation embrittles at the continuous high temperatures in the interior of the RTG. Despite maintaining a positive pressure of argon in the RTG, oxygen will slowly back diffuse past the C-seals and gradually degrade the interior components.