The constructor is required to activate the Guardian which is inside the Forerunner Facility on the North, but you need to face off enemies at Karken Battle Station before getting inside. Let's Checkout another Locke and Fireteam's adventure at the Karken Battle Station in Mission 10: Enemy Lines.
Your Main objective is to retrieve Halsey's Constructor, after reaching the rally point the Arbiter will give you the green signal so Starting with the mission, keep left and jump over the rocks to another side. use your D-pad for help. Head straight until you encounter few Covenant ahead. After defeating them check on the left corner for the Intel.
Head straight to the open area where Arbiter will give a green signal and help you with the clearing out enemies. Now move forward and you'll come across a Huge Staircase which leads you to a new section. You will be attacked by some Grunts and few other enemies so quickly take them down and keep moving.
Once you done with the enemies you'll be asked to bring down the Shield by shooting it. If your out of ammo take a look at the hole in the rock nearby where you can get to the other side and shut down the Shield generator and continue moving. Now look at the right there is few canyon so simply hop on it and lets head towards the Temple Ground which is between the Osiris and the Destination.
As you move forward watch out for the enemies, keep eliminating them and make sure you don't take much damage as too much damage will destroy the canyon. Moving forward you'll have to leave the canyon outside and walk inside the cave until you come across another shield and here you need to use the full power to destroy it. After Destroying the Shield, you see the Temple's entrance.
Keep Eliminating the foes that come in your way, once you're inside the temple find the way to climb up the roof. Use the D-pad to locate the jump. Make use of the set of the Stone ledges to climb up, then scan the Stone Device to open the door which leads us to Dr. Halsey's coordinates. As you head inside the door you'll be attacked by few more Prometheans so take them down, please.
You'll team up with the Arbiter against the Karken's soldiers so Mount on one of the Phantoms and take the Karkens down. Later Tanaka will ask you to land on the Karken and fight these soldiers and find the generator on foot. After hitting the Generator, you need to escape the Karken so quickly find some Phantoms or Banshee and get the hell out of there.
Time to grab the Halsey's coordinates which are inside the Forerunner site. Scan the area and locate the Gate/entry point. Once your inside leave the banshee and start moving forward on foot. Locate the Constructor and break the panel you'll notice the contractor will start following you.
Defeat the enemies coming in your way and head straight towards the base camp where Arbiter has sent the Phantoms for you to pickup. The cutscene will start and end of the Mission 10: Enemy Lines.