Not necessarily. It's hovering there, but its engines are damaged so it can't leave.  Escape pods would go downward to the flag below.  When the Imperials drop to that flag and take it, it's their base (with, say, tanks lifted down from the ship), but it can always be taken back by Rebels (perhaps as a push-map, or even Assault-Lines...?). 

Imps have to take the rest of the map working outward from their 'base' before their ship is destroyed by the rebels...  Alternately, Imps have unlimited tickets until the ship is destroyed.  Or, maybe it's just static and non-destroyable and the Rebels have to conserve their tickets...

Rebels are limited by weaker weapons, so it takes a while to blow up the Carrack. All their fire would be from the ground, so Imperials could see where the attacks are coming from -- they just have to get there, kill the Rebels and take the flags.