An electric power supply, small enough to be man‐portable, is being developed for remote, terrestrial applications. This system is designed for an operating lifetime of five years without maintenance or refueling. A small Radioisotope Stirling Generator (RSG) has been developed. The energy source of the generator is a 60 watt plutonium‐238 fuel clad used in the General Purpose Heat Sources (GPHS) developed for space applications. A free piston Stirling ENgine drives a linear alternator to convert the heat to power. The system weighs about 7.5 kg and produces 11 watts AC power with a conversion efficiency of 18.5%. Two engine models have been designed, fabricated, and tested to data: (a) a development model instrumented to confirm and test parameters, and (b) an electrically heated model with an electrical heater equipped power input leads. Critical components have been tested for 10,000 to 20,000 hours. One complete generator has been operating for over 11,000 hours. Radioisotope heated prototypes are expected to be fabricated and tested in late 1995. © 1995American Institute of Physics