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A new generation of radioisotope space power systems based on AMTEC (Alkali Metal Thermal to Electrical Conversion) technology is presently being developed. The future application of this technology, as the electrical power system for outer planet deep space missions, is ultimately dependent on it being robust enough to withstand the mission’s operational environments (high temperatures, dynamic loadings, long mission durations etc). One of the critical material selections centers on the cell wall whose physical and chemical properties must provide it with sufficient strength and material compatibility to successfully complete the mission. Niobium-1%zirconium has been selected as the cell wall material for application in the new radioisotope space power system being developed as part of the ARPS (Advanced Radioisotope Power System) program being supported by the U.S. Department of Energy and NASA.

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.