List of nuclear power systems in space

This list of nuclear power systems in space includes nuclear power systems that were flown to space, or at least launched in an attempt to reach space. Such used nuclear power systems include: Systems never launched are not included here, see Nuclear power in space.
 * radioisotope heater units (RHU) (usually produce heat by spontaneous decay of 238plutonium)
 * radioisotope thermoelectric generators (RTG) (usually produce heat by spontaneous decay of 238plutonium and convert it to electricity using a thermoelectric generator)
 * miniaturized fission reactors (usually produce heat by controlled fission of highly enriched 235uranium and convert it to electricity using a thermionic converter)

Initial total power is provided as either electrical power (We) or thermal power (Wt), depending on the intended application.