You need to walk right up to the door to trigger the opening mechanism. I experimented with bigger trigger volumes but it turned out to be more annoying than useful. There are two doors in the project that should automatically open for you, The entrance to the NGA and the office door with the glass panel inside the NGA. Please let me know if the doors don't open when you walk right up to them. You can see here in this video at the 28:21 minute mark how the doors should open for you...