First search the surface for a dark and deep crater on the moon, then make sure you have blocks to get out of the hole. Jump down the hole when ready. Take some glowstone torches or glowstone blocks with you for lighting up the tunnels of the dungeon. In some rooms of the dungeon there will be mob spawners on the floor. Break them as soon as you can before you are overwhelmed. You will also find rooms with chests in the dungeon with treasures in them, and once you have reached the boss room (a big room with lava pillars in the corners) an Evolved Skeleton Boss will spawn. He will shoot arrows at you, pick you up and throw you at the pillars and he will drop the tier 1 dungeon key when killed. Take this key when you kill him and proceed to the main treasure room. You can identify this room with a red chest in the middle with glowstone pillars in the corners. Right-Click the chest and you will unlock it. Right-Click again to open it up, it should contain a schematic for a tier 2 rocket, the moon buggy, or both.