Fighting Tartarus Without Fighting Brutes
From Halopedia, the Halo wiki
After Sgt. Johnson destroys the door of the Control Room, go inside and activate your Active Camouflage. Then go straight to the door on the right side of the room before it closes. If done correctly, you should skip straight to the cutscene with Tartarus. Also, if you bring a Banshee with you, the Banshee will be sitting in the hallway behind you. If it is not there, throw a Plasma Grenade at the four Brutes, then ride the platform with Miranda Keyes and blast Tartarus with all of the saved ammunition.
On the other hand, if you get a Banshee through the front door, you can boost in the second door, thus skipping the Brute fight and going straight to the cutscene.