...Indeed, the use of "probe" for crewed missions would probably be preferable in TOS "Tomorrow is Yesterday", where Captain Christopher's descendant is credited with leading the first "probe" to Saturn. It's much more glorious if he commands a crewed mission there than if he coordinates an unmanned flight (which by all rights should have taken place much, much earlier in the Trek timeline, and indeed would already have been in planning when the episode was filmed).
Of course, "probe" may also mean an investigation of non-exploration sort. The young Christopher might have been leading a legal inquiry into a badly botched first flight to Saturn, but again it would be less glorious than him commanding a crewed rocket flight there.
Lately I have assumed that Colonel Shaun Christopher led an unmanned probe to Saturn. Mostly because in his lifetime, we should not have been making manned flights that far out.
We don't know how old he was when this mission took place, but we *do* know - now - that the first flights to Mars were in the 2030's ("One Small Step"). The Colonel was obviously not yet born when "Tomorrow Is Yesterday" took place, in the 1960's. So assuming Shaun was born in, say, 1970, that would put him at 60 when the first Mars flights occurred. A manned flight all the way to *Saturn* would of course have to come after that. And wouldn't 60-70 years of age be a bit old for someone who's a Colonel?
Then again, a flight to Saturn would not have to be manned in order to be significant. If it was, say, an automated probe controlled by telepresence from the ground (possibly by the Colonel himself), then that would surely be just as important, wouldn't it?