In the Space Frontier booth, you will come to the Launched In Space mini game. Zerg appears in the center planet. But only when shoot all the green and red balls on the rotating rings around the planet. After, there will be four planetoids that will pop from the bottom. Hit all of those to make the plant split open and reveal Zergs head. You can do this at any point of the level. The sooner the better. You might have to do this twice during the level to get a total of 30 hits. But its very doable in attempt. Holding down will rapid-fire continuously.