We started doing sketches based on [Paul Christopher's Discovery concept and the '70s Ken Adam & Ralph McQuarrie Enterprise design], but the first thing Bryan [Fuller] said when he saw them was that he didn't want to see any round nacelles on any Starfleet ships! That became a huge concern for all of us, because we were all thinking, "No round nacelles, what are we going to do now?"
Since everyone knew our timeframe took place between Enterprise and the original TV series, round nacelles would really sell the timeframe without question, so having to alter them on all our starships was strange.
We were probably 90% of the way there in the first month or so, but the nacelles became a big holdup. It ended up being a battle for easily five months, just trying to figure out what kind of nacelles we were going to do, and we tried every shape possible.
(Pages 183-184)