Plus you can fortify just one planet, and use phase stablizers to quickly reinforce your main fleet. Anyways, if vasari could build ships on the move...THE STRIPPED TO THE CORE RUSH WOULD BE UNBEARBLY BROKEN.
They can. It's called Spawn Phase Stabilizer. It's an ability on the Vorastra. The spawned planetmodule allows the VL player to spawn combat ships, support ships, and capitalships.