During the Defenders of Man Insurgency, the Defenders of Man drew the Tal'darim into the conflict by attacking one of their remote outposts, and the Tal'darim Death Fleet met them at Tyrador IX. After clearing landing zones, they warped in four shield projectors, which they used to channel energy into their mothership. Agent Nova Terra, knowing the Tal'darim would kill the civilians the Defenders were protecting, set out to destroy the shield projectors. She was successful, rendering the mothership vulnerable and allowing her forces to destroy it.
Shield projectors are the primary objective of the second section of Trouble in Paradise. They are scattered through the map, and defended by moderate protoss defenses, including photon cannons and oracles for detection. The defenses surrounding them can be either brute forced with a force of marines, siege tanks and goliaths, or bypassed using cloaked banshees to take out areas covered by only a single cannon. Alternatively, nukes can create holes in their detection, allowing banshees to slip in and destroy the projectors.
As long as the shield projectors are active, the mothership is invincible. Destroying one temporarily removes the mothership's invincibility, prompting it to teleport back to base. When all projectors are destroyed, the mothership can be damaged.