The Apollo Service Module is the bottom half of the Apollo CSM. You can put any small payload or capsule on it, and the module can act like a second stage. The Apollo Service module is used in various missions and programs such as the Apollo Moon Landings and the Apollo-Soyuz program. This is included in the construction of the Saturn 1B.

The Service Module historically is powered by fuel cells, running off of batteries in the game. The Service Module is a small size in-game, and is the core of the Apollo spacecraft.