“Disrupt Rasputin's defense by shorting out the local servers.”
Head down the tunnel into The Mine. This leads to the second Rasputin Bunker in the Cosmodrome. Head forward and through the doors. When you arrive in the Coolant room you better reload and get ready for a massive wave of enemies.
When things begin, you will face a number of Exploding Shanks that come from the vents in front of you. There are at least four. Take them out quickly because one can easily kill a Guardian at this difficulty level.
Get through the wave and will hear from Ghost. You need to disable Rasputin's defenses. Head to the far end of the room. One member of the Fireteam needs to throw any kind of grenade into the open hatch. This will open the door forward.