Continuity mistake: When Elaan visits engineering, the close-up shots of Scotty show a security guard wearing a black utility belt standing in the background. But the man is missing in all the full shots. (00:13:15)
Continuity mistake: As Kirk wipes a tear from Elaan's face, both cheeks are wet. A second later, both cheeks are dry.
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