In Skirmish, you advance tech levels by purchasing the next level of each station. In GC, there are no true tech levels. Instead, you research the ship designs and advanced models of the ships you want. For reference on how to get to which ships, you can check out the tech tree images included in the mod folder.
Each Space Station level is associated with different size ships.
Level 1: Fighters/Bombers/Transports
Level 2: Corvettes/Freighters
Level 3: Frigates/Cruisers
Level 4: Destroyers/Capitals
Level 5: Dreadnaughts
The more of one Space Station level you build, the faster those types of ships build.
k thanks thats really really nice to know...