Gnome Stew has an interview that gives more information about STA.

Interview With Chris Birch About Star Trek Adventures

Chris Birch (CB): At the moment we’re thinking of one core book, but there will be Division books that expand character generation, say for more detailed science adventures, as well as providing the GM with loads more relevant support, plot seeds, etc. We’ll also have books for each Quadrant that introduce other playable races, empires, etc.

KG: Your website mentions that “the core rulebook will focus on playing human and alien Starfleet characters.” Can you tell us which Starfleet aliens will be playable on launch?

CB: We haven’t decided yet–of course there’s lot of them so we’ll focus on the more popular ones, then add more in each of the Quadrant books.

KG: Do you expect to publish setting material in books divided by era (original series, next generation, etc.), or combining those in the same books?

CB: We intend to include the material in the same books–so the Division books will cover different equipment by era (we’re really focusing on two–the Original Series and the Next Generation Era) and the Quadrant books will cover key events and changes in technology or empires between the two main eras.