There has been a lot of work on space nuclear reactors, though I don't believe any have used Thorium. It can probably be compared to these older reactors.
Notable uses for nuclear fission reactors include:
- Providing power in the outer planets and beyond where there's not enough sunlight
- In those situations, having hundreds of kilowatts for radio transmissions would enable vastly higher bandwidth comms.
- General purpose power sources as you describe
- Nuclear-electric propulsion -- large reactors provide enough power for ion or other electric plasma thrusters.
- The various improvements that become possible when a large source of power is available.
Check out the SNAP project, and RORSAT.
Note that a reactor is normally placed at one end of a spacecraft, not the middle. This allows one to get away with only shielding one side of the reactor.
You also can make Nuclear Thermal Rockets using nuclear reactors; these have twice the specific impulse of chemical rockets and fairly high thrust. They use very specialized (and insanely high power density) reactors, and I don't think there has been any research in fueling them with thorium.
A number of (non-thorium) nuclear reactors have been flight tested. Ironically, most of them were not in any of the above applications where the use of a nuclear reactor is