jeff findley wrote:

Even better would be a dual mode nuclear engine that could produce
high thrust exhaust or electricity. Use the electricity for cruise
mode where something like an ion or plasma engine is more efficient,
but use the high thrust nuclear engine for entering and leaving
the planned planetary orbit (to save time).

One can also design a nuclear engine that produces some electricity
with the propellant itself. There are large unnecessary entropy
producing steps in a conventional nuclear thermal rocket (for example,
when injecting cooler propellant into a hot thrust chamber); it's possible
to design the engine to instead extract additional work. This would not
require external radiators.

One could use this electrical energy in a kind of arc afterburner
downstream of the reactor, to heat the propellant to above the
temperature limit of the reactor's materials.

Paul