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takeoffs are optional; landings are mandatory
It's probable the engineering was moved during the pre-TMP refit. There was probably more evidence, but i am tired today and cannot remember.
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Gene: "I AM Star Trek"
Yvonne: "You can't sum yourself up in so small a package."
Gene: "SMALL?!!"
- Gene Roddenberry: The Last Conversation
While there are hints in TOS that engineering was in the saucer, other hints exist for a secondary hull location. The energy entity in "Day of the Dove" leaves engineering through the secondary hull skin, as seen in an exterior view. Turbolifts run vertically inordinately long to reach engineering (although sometimes a trip from bridge to deck 2 can take an eternity, too!). Not only impulse power but also warp power is manipulated through the engineering facility. And Scotty does go "down to engineering" when he leaves his bridge station.
Timo Saloniemi
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takeoffs are optional; landings are mandatory
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The Starship Encyclopedia
There could of course be two or more engineering stations on the ship, but it seems awfully odd that the "impulse engineering" station would feature the dilithium crystal holder thingamabob in the middle of the floor - or that the "warp engineering" station would have the same tubes behind the red grille that are associated with the impulse engine in some episodes.
Having the engineering in its ST:TMP location would help keep that refit a bit less extensive. Having it in the saucer aft rim would help explain why Khan was able to cut off "lower decks" yet preserve access to engineering (although one could also say that the diagram next to the turbolift, with color-coded interiors, shows us that there was a narrow region running through the vessel and isolated from the rest of the ship).
Timo Saloniemi
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Dane
"...and there was war in heaven..." The Bible, Revelation 12:7
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"If you attempt to return the device to the store, and you are missing one single peanut, the store personnel will laugh in the chilling manner exhibited by Joseph Stalin just after he enslaved Eastern Europe."
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takeoffs are optional; landings are mandatory
I looked at my tape of "The Enemy Within", and there are two shots of the evil Kirk as he crouches atop some machinery. The camera shoots up at him, and you can see the ceiling - and it indeed is curved. It looks like the top of the secondary hull.
Also, in the previous scene, Spock asks Kirk where he'd hide to elude a mass search, and Kirk answers, "The lower levels. The engineering deck." Obviously, lower levels must refer to the secondary hull and not the saucer. We could interpret his statement as meaning the engineering deck that is located in the lower levels... not that the only engineering deck on the ship is located there.
The engineering deck where they search for the evil Kirk looks quite different from the engineering section used in the second and third seasons, which was much larger and had an upper level. I would postulate that the larger section with the upper level is located in the saucer adjacent to the impulse engines, while the other is down in the secondary hull.
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The Starship Encyclopedia