Matt Jefferies had anticipated the need for a flight or hangar deck when he designed the original Enterprise, providing space in the aft section of the engineering hull for just such a location. But when the episode “The Galileo Seven” was supposed to unveil it, there was no way budget would allow for a full-scale set of bay to be built.
Jefferies recalled in an interview with Star Trek: The Magazine (April 2000) years later how the “curved clamshell doors at the back” of the ship “didn’t look too much different from a lot of today’s modern hangars on the inside.” He took care to scale the bay’s design to the shuttlecraft that were supposed to fit in it. “The shuttlebay itself was only in miniature.”
Geoffrey Mandel’s U.S.S. Enterprise Officer’s Manual (1980) puts a flight deck control tower above the shuttlebay doors:
Richard C. Datin was commissioned to build the maquette. Star Trek: Communicator (June/July 2001) quotes him explaining how the starboard side of the miniature was supposed to be removable, so the scene could be filmed from more than one side.
However, for whatever reason, the starboard wall was not made to be removable and filming of the miniature could only be done looking back to the clamshell bay doors.
Hence the familiar scene from “The Galileo Seven.”
The clamshell doors were hand-operated, as were cables that controlled the revolving platform in the center of the set. Footage shot at Dunn’s Film Effects was replicated throughout the rest of the series whenever a scene called for it. The maquette was probably destroyed.
When the episodes of the The Original Series were digitally remastered in 2006, the shuttlebay scenes were replaced with CGI imagery.
Max Gabl did the matte painting, which premiered in the remastered version of “Journey to Babel.” Much more detail can be seen and the access corridors to the sides of the landing bay are extended.
In the remastered version of “The Galileo Seven,” a second shuttlecraft was inserted to make the scene visually more interesting.