The airship would essentialy be carried by Venus' high wind most of the time, so the disk shape works for that. It also had to be inflatible on the spot, and this shape meant easier stowing. And simple geometric shapes are clean and striking.
I was also simultaneously designing the set for the cabin interior. Here are renderings of that.
Main cabin front and side views. The "dog nose" bulge on the front houses a large radar antenna. Those "rails" visible in the front view leading down from the bases of the engine pylons are there so the engines can be folded down for storage during planetary transit.
For plot purposes the airship needed three different hatches for entry and exit. Bottom of cabin, rear of cabin and top of envelope, reacheble through a collapsible tube.
The airship with its base, the Daedalus Platform in the background.