Idk about that. I recently played a game as Mongolia with Rome running away with me just to my east. We were neck and neck on space ship progress, so I stacked my modern armors, missile cruisers, and nukes, close to his border waiting, but he beat me to victory before I made the move (by 4 turns I later found out). So I rolled back to a save from 5 turns prior to his winning, and started the assault immediately, dropping 2 nukes on the first turn, and the third nuke on the 2nd turn (I'd imagine by reducing his pop, he suffered production losses). I continued my assault for two more turns and captured Rome (his partially finished spaceship still standing there), while mine blasted off to a "brave new world" about 5 turns later.
So I can't say whether I took completely over his spaceship production by taking his capital, or if I just slowed his production so much that I held out for victory.