In the "Disable Pulse Generators" mission, you have to disable four Pulse Generators. After you have disabled the first two Pulse Generators (in the first part of the structure), get to the second part or the other side. When you get there, ignore the Raven that you are facing and disable the third Pulse Generator. It is located all the way at the bottom. Note: You should be on the other side, where the other Raven is located. Then, get to the fourth Pulse Generator. This Pulse Generator is in one of the doors with the air vents. Once you are in the room where the fourth pulse generator is located, destroy the vents on the top. Look up to find it. When you get to it, do not disable it. Look up again to see that there are air vents that are already open. Go to it and turn left to find the Stealth extension part.