While not reactors technically, many of our long-range spacecraft use RTGs: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator https://en.wikip

While not reactors technically, many of our long-range spacecraft use RTGs: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...