It's not just about Scotty knowing what to do, it's about the audience knowing what Kirk is telling Scotty to do. If it's to detach the saucer section and allow the secondary hull to be destroyed, the dialog needs to say that. Kirk could tell Scotty to separate the saucer section, but he doesn't. He says jettison the nacelles.
Now we have to think about what these 1960s writers thought of as "nacelles," not what we fans think of today, in an age Starfleet ships live by a decades-known set of established terms.
In this case, jettison the nacelles was in response to:
This also assumes that the matter and antimatter reactions are in the nacelles, only, and not in the secondary hull. It's always vague with this show.
A couple of years ago I was at The Star Trek Original Series Set Tour for a Shatner event. When I visit my friends there, I love to help out with the guests and stay out of their way. I didn't expect to have a "fist fight" with William Shatner!Normally my friend John Carrigan Does the honor, but John was unable to attend. While waiting outside the entrance to engineering ,out of the way of the guests, I hear my name called! James Cawley came out to meet me and said...You're Fighting Captain Kirk!So there I was standing in front of Mr. Shatner as he explained to the guests how he would Kick my butt!We did it twice that day. The second time Mr. Shatner and I waited for the guests to move on to the bridge.He then said to me, you did a good job. I said thanks! He then said John Carrigan would have fallen on the floor! I said, OK, next time I'll do that! Mr. Shatner looked at me in my full Starfleet uniform and said, No, I wouldn't want you to dirty that tunic...It looks expensive!A great memory! Luck would have it that several of the guests sent me these images as I was too busy acting!To do this, in full uniform, in engineering on the Starship Enterprise, acting a fight scene with William Shatner was a very surreal event indeed!
Separating the saucer section was also mentioned as a possibility in TOS writer's guide, but it would have been expensive to film so they never did. Besides, the saucer would have had no warp drive, so they'd be marooned wherever they were unless they could get a subspace message out, and the engineering hull would lack a transporter room and probably phasers.
The plot of The Enemy Within wouldn't have made sense if they had another one.
If they did, whichever hull had the central gizmo would have been the only one with a working transporter in the event of hull separation.
You're entirely right, but after a hull separation the Connie with multiple Transporters would be no worse off than the Connie with one.
How is being able to escape the ship in a hurry going to be a big advantage? Most of the time, the Enterprise is exploring someplace remote, and there would be no other ship around to pick up escape pods before their air ran out. Eventually they got shuttlecraft, but even with the shuttlecraft packed beyond it's rated capacity it would take many trips, and unless they were incredibly lucky there's not much of any place to go with it that would be safer than the ship.
