> if we had not already launched several nuclear reactors into space.
AFAIK, we haven't. What we have launched several of are RTGs, which other than using nuclear fuel, are a completely different technology, one which is much easier to completely shield. IIRC, there have even been cases where a rocket containing a RTG failed, and the RTG was found intact and could even be reused.
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"
"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)"
Sure, but the (perceived) popular resistance is to the risks of launching nuclear material, and that is no less for RTGs than for "real" reactors.
Nobody would be all that upset about launching an unfueled reactor, since that is basically just a collection of pumps and turbines not fundamentally different from anything we already shoot up. You could/should even launch the fuel and reactor in different rockets, so that you have more mass budget for wrapping up the fuel rods extra safely.
I think you're assuming a false premise, that everything nuclear in space is an RTG.
It's always possible I've been reading misinformation, but allegedly the major source of radioactive debris in orbit is defunct nuclear reactors that collided with something, and they also interfere with gamma-ray observations.
So if it is indeed true there are many satellites powered by reactors, it couldn't be obscure, many people must be aware.
