“Descend into the Cosmodrome tunnels and use Ghost to link to the information hub.”
Turn to the nose of the ship. Look to the right from there to see the first beacon that will start you toward the information hub. Head around the building. Be careful though as there are a number of Fallen patrolling on the left-hand side of it. The problem is the left-hand side of that building has the entrance you are looking for. You can either engage these Fallen or just slip past them:
Once inside the building head straight for the back. Take the stairs down to the right. Head on through the door just ahead of you. After that go through the door in front of you and follow the passage to the left. Just head across the next room. You will find the room you're looking for:
Head over to the map of the area. Here you'll be able to Deploy your ghost to access the network for the first time.