Attack of the Moon Zombies

In the year 2048 the Nation Space And Exploration (NSAE) team landed on the moon in hopes of colonizing the desolate environment. Three months after they first landed on the moon, the NSAE team encountered complications with their newly structured dome city on the surface of the moon. The team came up with a new plan to colonize under the surface for better protection against the hard environmental conditions. Two years after sustainable a colony under the surface NSAE found people were starting to disappear and that strand unexplainable deaths were happening. No one really knew what was going on. Everyone thought that people were just making mistakes and opening rooms without air or walking in areas that civilians shouldn’t be in. They were wrong.
Now the colony is under attack! Zombies have evolved and survived on the moon and now are starting to attack the colony. The only way into the colony is through a five foot diameter sewer main on the surface.
Your are a level eight NSAE moon warrior and your mission is to guard the sewer at all costs while the rest of the team searches other parts of the moon for zombie colonies. Use your NSAE certified Machine Gun, Rocket Launcher and Sniper Rifle to keep the zombies away!