>AFAIK, we haven't From Wikipedia, there are (or were) over 30 reactor (not RTG) powered satellites. One program was called "US-A" and another "SNAP-10A". Thes

>AFAIK, we haven't From Wikipedia, there are (or were) over 30 reactor (not RTG) powered satellites. One program was called "US-A" and another "SNAP-10A". These were launched at least from the 1960s through the 1980s, by multiple countries. "The US-A programme was responsible for orbiting a total of 33 nuclear reactors" "Normally the nuclear reactor cores were ejected into high orbit (a so-called "disposal orbit") at the end of the mission, but there were several failure incidents, some of which resulted in radioactive material re-entering the Earth's atmosphere." "The higher-orbiting TOPAZ-containing satellites were the major source of orbital contamination for satellites that sensed gamma-rays for astronomical and security purposes, as radioisotope thermoelectric generators (RTGs) do not generate significant gamma radiation as compared with unshielded satellite fission reactors" https://en.wikipedia.org/wiki/US-A https://en.wikipedia.org/wiki/US-A "The [SNAP-10A] reactor measures 39.62 cm (15.6 in) long, 22.4 cm (8.8 in) diameter and holds 37 fuel rods containing 235U as uranium-zirconium-hydride fuel.[15] The SNAP-10A reactor was designed for a thermal power output of 30 kW and unshielded weighs 650 lb (290 kg)" https://en.wikipedia.org/wiki/SNAP-10A https://en.wikipedia.org/wiki/SNAP-10A