here we are

Rear nacelle view of second pilot Enterprise on soundstage, 1965 (by birdofthegalaxy):

A blue screen soundstage shot showing the details of the “grid pattern” at the rear of the nacelles used for the large eleven foot Enterprise model during its first full episode filming for the second pilot, “Where No Man Has Gone Before.” […] (this pattern would only exist for this second pilot and the stock photography done on the model, during the filming version it was replaced by a sphere like shape).