posted
I notice two additional items not mentioned, to the best of my knowledge on this board or other boards, in the opening credits.
First, Mercury Capsule. In one of the blueprints shown, there is the drawing of an Atlas rocket with the Mercury Capsule snuggled in at the top. The words "MERCURY CAPSULE" are readable.
Second, unknown ship towards end of credts. This ship which has been discussed before I think is the immediate predecessor to the Enterprise NX-01. Both ships feature up-swept pylons, a supporting structure between the nacelles, and a forward primary hull. I think the large engines seen in the center of this ship are the impulse engines, which are later placed more to the side on the later ship. This is to make room for the weapons module.
posted
I'd think the difference between these big round rocketlike impulse engines and the arbitrary-shape, typically narrow impulse nozzles of NX-01 should count for something, too. LaForge says in "Relics" that impulse engines haven't changed much in the past 200 years, meaning the last major change took place in the mid-22nd century. Perhaps we could nail it down as having happened between these two ship types?
After this opening-credit vessel, I don't think we have seen that many or that large impulse nozzles in other designs. The NX-01 is an intermediate step, after which three separate nozzles becomes plenty, and four (as in Akira) is something like the absolute maximum.