As most of us have seen in the teaser for JJ Abram's upcoming Trek movie, the original Enterprise was obviously -to some extent- built on Earth, namely at the famed
San Francisco Naval Shipyards. Now, I have seen some fans complain that this was, in fact, not canonical to see it depicted as such.
Is that true? Well, let's examine some examples:
1. Ships are regularly built planetside, as shows this image of
Utopia Planitia 2.
According to The Making of Star Trek, the Enterprise was built on Earth but assembled in space.
Source3. It has never been established on-screen that the original Enterprise was completely constructed and assembled in space.
4. It would make sense to construct the ship planetside but assemble it in orbit. Why you ask?
Well, it's quite simple, actually: Having assembling crews in a zero-g environment construct each and every component
by hand in EVA-suits would be way too impractical to actually pull it off. Instead just assembling the bigger
components in low orbit would even profit from the low gravity and could be done by worker bees or somesuch.