Revealing mistake: As Spock carries the crewman, the second spear hits a rock. As it does, you can see the Styrofoam chips fly up.
Revealing mistake: After Spock finds Gaetano's body he carries him back to the shuttle, and in the interior shot as McCoy and Boma carry Gaetano's body to the back, we can see though the shuttlecraft's doorway the top of the set's blue backdrop.
Revealing mistake: The stuntman playing Latimer is obvious when he falls after being hit in his back with the creature's spear.
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