You land nearby the entrance to the vault of glass itself. Summon your sparrow and make your way from the landing point toward the front of the Vault. There are a number of Vex in the area. Until you reach the entrance to the Vault of Glass, they will be trying to kill you.
When you make it to the front of the Vault, you will see those are just standing there ... waiting. Ghost will remark on this. Just let the Vault door open. You do not need to destroy any of these Vex units.