The Department of Energy (DOE) and the NASA Glenn Research Center are developing a Stirling converter for an advanced radioisotope power system to provide spacecraft onboard electric power for NASA deep space missions. This high-efficiency converter is being evaluated as an alternative to replace the much lower efficiency radioisotope thermoelectric generator (RTG). The current power requirement (six years after beginning of mission (BOM) for a mission to Jupiter) is 210 W(sub e) (watts electric) to be generated by two separate power systems, one on each side of the spacecraft. Both two-converter and four-converter system designs are being considered, depending on the amount of required redundancy.Juhasz, Albert J. and Tew, Roy C. and Thieme, Lanny G.Glenn Research CenterSPACECRAFT POWER SUPPLIES; POWER CONVERTERS; SYSTEMS ENGINEERING; RADIOISOTOPE BATTERIES; RESEARCH AND DEVELOPMENT; STIRLING CYCLE; SPACE MISSIONS; THERMOELECTRIC GENERATORS...