The original Excelsior was a physical filming model designed by Nilo Rodis and Bill George and built at Industrial Light and Magic for Star Trek III: The Search for Spock. The model also appeared in The Voyage Home and Star Trek VI: The Undiscovered Country and was relabeled for use in the first two seasons of The Next Generation. The model was again refurbished with entirely new arrangements and details to represent a refit modification, the Enterprise-B, in Star Trek Generations.
The refit modifications were designed by John Eaves under the supervision of Herman Zimmerman. Since the original model was no longer in its original configuration, a new one was built by Greg Jein when the Excelsior appeared in the Voyager episode “Flashback,” if at a smaller scale. This model continued to be reused until a CGI Excelsior was built for later seasons of Deep Space Nine and Voyager.
Although the Enterprise-B had already been established as an Excelsior-class starship, the producers of Generations felt the Excelsior had been seen too many times in previous films. They wanted a brand new design. This presented a challenge to the movie’s art staff. How to maintain continuity while giving the audience a “new” ship?
John Eaves writes in Star Trek: The Next Generation Sketchbook, The Movies (1998) that the Excelsior has always been his favorite starship. “Bill George’s design conveyed power, elegance and beauty, so when the task fell to me to modify the ship, I was both thrilled and concerned.”
Fortunately, Mike Okuda came over to the feature art department to discuss changes that would significantly alter the ship’s appearance while keeping her original lines. […] His focus and direction for the modifications were extremely helpful. So together, we set to work on the details.
First, Eaves took an ILM photo that showed the Excelsior in Spacedock, did a rendering and started putting detail on the ship. Okuda pointed out they needed to design an area that protruded from the ship, so the Nexus energy ribbon could whip out a section while leaving most of the ship intact.
So we built a section of decks extended out from the main body, which tapers gently on the bottom and flares out dramatically on the top. We also did a detail sketch of the area round the deflector disk, designating one area as the reactor room.
The added girth increased the overall size of the vessel, while still retaining the original Excelsior design. We made a few other design changes, such as taking two fins off the top of the saucer, and putting in two major impulse engines, one on either side of the existing impulse engines (we figured these stronger engines would be needed when the saucer detached). As for the nacelles, we added a cap to them, plus a dorsal fin on top and a running fin on the outer edge.
Sources for this story include: John Eaves and J.M. Dillard, Star Trek: The Next Generation Sketchbook, The Movies (1998)