That is weird. The abrupt atonality of that transition is so at odds with the melodic portions before and after that is seems Horner had a very specific idea he was trying to convey. I wonder if he had to compose some of the music prior to the finished cut. I recall seeing and interview somewhere where ahorner said he had even less time to score III than he did II. The bridge lighting up is an effects shot -maybe Horner was given a different idea of what the transition would be like? Some ambitious zoom in on space dock from earth with a push in on the Enterprise that got scaled back? Or maybe and older draft of the script gave more detail on what Uhura did after the Mr. Adventure scene. The sequencing of the film was changed in the edit (with the Grissom /genesis into pushed back later in favor of opening with the Enterprise, so I maybe there was talk about doing some pickups to bridge that sequence?
Unfortunately we can’t ask Horner anymore. Wonder if the music editor Robert Badami ever visits the board.
On another note that sequence confused me a lot as a kid - the way the bridge lights came on made it seem to me like they were windows and the light was coming from the inside of the bridge. I kept trying to find those “windows” in the inside of the set, thinking they were up on the ceiling somewhere.
