That production "gutted" one of the Jupiter II filming miniatures, sawing additional "windows" into the upper hull and mounted it upon a column for part of the "city".
I can never forgive them for that!
(And before someone makes the effort to compose and post an overly long essay about the economics of prop, costume and set "recycling", I'm being melodramatic for comedic effect. It's a joke, son!)
That is still a real shame, though! That is the hero ship of an iconic TV show and part of television history!