And what Probert had to tell Drexler about the design:
This whole idea came about when a fan suggested that I design a new Starfleet Deep SpaceTug & Repair Ship for the calendar a couple of years ago. I already was into another idea at the time but started playing around with the idea because it intrigued me. As time went by, I continued to sketch up various concepts but nothing looked quite right. I eventually expanded it’s roll to lifeboat rescue (the four docking ports on top) added a shuttle bay, a mid-hull cargo section, and more clearly defined the ‘service deck’ (flat area on the “bottom”) which incorporates an inverted gravity field within it’s two decks. That allows those working on repairing & servicing smaller ships that have “landed” on that surface to have a ‘heads-up’ orientation to that surface. Incorporating it’s own exterior gravity plates, ships and personal could use it as an Earth-bound strip of tarmac. With flexible side ‘arms’ extending from the sides, that same surface may also be used to store large (or segments of) ships for transport to a repair base. Two tractor beam emitters are mounted at the rear for towing, with cable winches available as tangible backups. Finally, there are the obligatory phaser strips as a security measure.You can see lots more sketches of the tug on the Drex Files.
UPDATE: A cross section of the tug has been added to the original article, check out the inverted gravity: