T'Girl said:
How did Kirk and company know that Daran Five wasn't the intended destination?
Well, Yonada was on a
collision course with the planet. And there was an obvious discrepancy in the control room:
SPOCK: There seems to be a weakness in one of the eight tubes.
KIRK: Enough to turn it off course?
SPOCK: Yes. Let me check that engine. A very simple problem, easy to correct.
SPOCK: I believe we can attempt the course correction, Captain.
KIRK: Good. Going back to marked headings.
SPOCK: Guidance control's taking over. I believe we can allow this ship to go back to its automatic control.
KIRK: Steadying on course marked in red.
So, there was a definite course specified (in red) and Yonada had deviated from it due to a an equipment flaw. Spock was able to correct the problem (astonishing that it was so 'easy to correct'--wouldn't the control system be more robust not to be tripped up by a simple problem?) and set controls back on course. Automatic guidance takes over afterward.
If Darren 5 was the intended destination, they wouldn't have been off course. And the trajectory would've been correct for an approach that would put them in orbit of the planet... which wasn't the case once the course correction was made.
KIRK: Fabrini descendants are scheduled to debark on their promised planet in approximately three hundred and ninety days. I think that we could manage to be in that vicinity at that time, if you wanted to thank the Fabrini personally.
Well, with that kind of precision, certainly the Enterprise would be able to determine the destination! But alas, no mention of any specific planet. It would've been fascinating to hear something like this:
UHURA: Captain, we double checked the information relayed to us from Mr. Spock. Yonada's destination is Octarius 2, which is in fact a Class-M planet that has no population to speak of; just a few nomadic visitors, probably prospectors.
The Fabrini were highly advanced and must have had some way of scanning the depths of deep space (considering the ship they created, perhaps some kind of probes were sent out). They find a suitable planet that they know is far enough away to take several generations to reach, so they build a world ship to take the people there. I wonder how they were transferred to the ship without knowing where they were going? They didn't appear to have transporter technology, so being ferried into orbit would have given the feelings of weightlessness. Perhaps they were sedated. Clearly, the inhabitants were totally deceived of their situation (being on an enormous ship with a destiny to another world). Even Natira didn't know of the true purpose. I suspect the Oracle would have informed her at the appointed time and then there would be the re-education of the population.