Let That Be Your Last Battlefield - S3-E15
Revealing mistake: Stock footage strikes again when Kirk orders the red alert. A shot of the bridge and view screen, with Kirk standing in front of his chair, once more switches Kirk out for a stand in, and Chekhov has gone and is replaced by what looks like from behind like a young woman or a man with a long neck. Also the central display between navigator and helm is now different from that earlier. (00:11:15)
Let That Be Your Last Battlefield - S3-E15
Continuity mistake: The planet Cheron is blue the first two times we see it on the view screen, but when the Enterprise enters orbit, and every time we see it thereafter, the planet has mysteriously turned red. (00:44:05 - 00:46:00)
Character mistake: Elaan says "If I have to stay here for ten light-years..." A light year is a measure of distance. (00:24:03)
Let That Be Your Last Battlefield - S3-E15
Revealing mistake: As Kirk turns all the way around to look at the newly arrived Bele, the shadows of the stage wiring is easily spotted at the top of the screen.
Chosen answer: If they're in orbit, they're being pulled along by the planet's gravity well, therefore, impulse engines would only be used for minor corrections and would be "on standby" while in orbit, but not active. (Like keeping your car idling without revving the engine and creating plumes of exhaust).
Captain Defenestrator
Thank you for the info.
Movie Nut