Matt Jefferies also designed the K7 space station from the classic Trek episode "The Trouble with Tribbles." (which was re-created for the ST:DS9 episode Trials and Tribble-ations). He did his home-work and studied the then-current cutting edge aerospace design. Close to where he lived in Los Angeles was the the Douglas Aircraft Company, then one of the worlds largest aerospace contractors (Douglas is probably the "D" in "DY-100"). Among the concept models created by Douglas was the so-called "Mexican Hat" inflatable space station.
The K7 space station made a brief appearance as a plastic model.