There's also a harvester to kill on that level by an archeological dig. After you blast the turrets - don't go in the research building, but go back the way you came. Walk up the hill and over the stone arch. As soon as you see the mobile artillery, turn left and follow the passage. You'll see a harvester - blast it for a tertiary objective credit then go in the archeological site for armor and lots of weapons. But you gotta fight your way back out hehe so get ready...Then go back to research facility.