Mission 3 - Nightfall
There are two data pads to collect in this mission.
Click on the spoiler tag to see the embedded video for this mission:
You will also unlock the following data pad achievement in this mission:
Collecting all 19 data pads will earn you the following:
I've created a playlist which has all individual missions and their data pad locations: https://www.youtube.com/playlist?list=PLspO7pYM5dalFVnsrpbWe...
Note: you can collect the data pad and reload checkpoint/respawn, and you will still receive the credit for this achievement.