Not really a mission. After completing mission 3 you get into this camp and run around and talk to a bunch of people. Then you have to jump into a cargo Pelican and when you land and mission 5 begins. So no fighting in mission 4.
Datapad locations are
Intel #1: You can find this one on the right side of station’s interior gate
Intel #2: You can find this one near the vending machine
Intel #3: You can find this one on a bin near the water tower
Intel #4: You can find this one on the top of Medical Unit building
Intel #5: You can find this one at top of water tower
Intel #6: Atop the supply shed near the water tower
Intel #7: You can find this one near the far gate
Intel #8: You can find this one near the Pelican
Datapad location source:
http://gameswiki.net/halo-5-guardians-all-intel-locations-gu...Edit: there is no skull in mission 4.