(The following work should not be regarded as part of the Star Trek canon.)
This is my design for a TOS-era cruiser (TOS = The Original Series for those not familiar with trekkie lingo). It has the same basic design as the Constitution class heavy cruisers such as the Enterprise, but is slightly smaller and more compact. The lead ship of the class, pictured here, is the USS Paul Dirac.
The class is intended to look as though it was built a little after the Constitution class, so it has a few early elements of TMP-era design (TMP = The Motion Picture, but you probably already figured that out). You can see this in the shape of the bridge for example, and in the way that the main deflector has been pulled back into the secondary hull. I also tried to give it a bit of an Excelsior-like look, most obviously in the shape of the saucer and design of the neck.
The biggest difference with the Enterprise is that this class has much greater accommodation for shuttlecraft and other small craft. In fact the secondary hull has two flight decks (shuttlebays), a smaller upper deck and a larger lower deck. The doors for the upper deck are on the upper starboard side immediately below the back end of the neck, while the doors for the lower flight deck are in the lower aft end of the hull. In an emergency the two decks could be used to launch and recover craft simultaneously, making this vessel similar to a through-deck cruiser (about which more later).
The upper aft end of the secondary hull, from the warp nacelle pylons and back (i.e. where the shuttlebay is in the Enterprise), is occupied by main engineering. The warp core eject mechanism is visible as a circular hatch with yellow and black markings in the tail end of the ship.
These ships would not be capable of the kind of extended five-year missions that the Constitution class is designed for; rather they would be used for shorter missions of maybe six months, or a year at the very most. I imagine the crew complement would be about 300. I decided to name the ships after prominent physicists, a convention that would seem to fit well with Starfleet's research and exploration brief. (Plus which, I studied physics at university and I've always had bit of a soft spot for Dirac.)
The inspiration for this design was the Coronado class through-deck cruiser described in Ships of the Star Fleet Volume 1 (published in 1987 by Mastercom Data Center), and pictured below. I ended up making a lot of changes though. While I liked the basic concept, I didn't like the way the warp engine pylons clearly intruded into the flight deck, nor the fact that the main deflector was missing. The Dirac class is my attempt to address these issues.
