Here is the full list of all 54 Sentinel 4: Dark Star achievements.
Kill 500000 enemies
Buy every upgrade in the armoury
Finish the campaign on Psycho difficulty
Reach maximum level with any Commander
Build 1000 turrets
Fully upgrade a turret in the armoury
Fire 1000 Sentinel orbital weapons
Use 1000 Stronghold abilities
Complete mission 5 of the second mini-campaign
Complete mission 4 of the second mini-campaign
Complete level 6 (Alliance) without losing any Xenite defenders
Complete campaign mission 26
Complete campaign mission 25
Complete campaign mission 24
Complete campaign mission 23
Complete campaign mission 22
Complete campaign mission 21
Kill 50000 enemies
Complete campaign mission 20
Complete level 10 (Titan) using only Laser Turrets
Complete level 2 (Fortification) using only path deployable weapons
Complete campaign mission 19
Reach Nexus rank 10
Complete campaign mission 18
Complete campaign mission 17
Complete campaign mission 16
Complete mission 3 of the second mini-campaign
Complete mission 2 of the second mini-campaign
Complete campaign mission 15
Complete campaign mission 14
Complete campaign mission 13
Complete campaign mission 12
Complete campaign mission 11
Complete campaign mission 10
Complete campaign mission 9
Use 100 Stronghold abilities
Fire 100 Sentinel orbital weapons
Complete campaign mission 8
Reach Nexus rank 5
Complete campaign mission 7
Build 100 turrets
Complete mission 1 of the second mini-campaign
Kill 5000 enemies
Fire 10 Sentinel orbital weapons
Complete campaign mission 6
Use 10 Stronghold abilities
Complete campaign mission 5
Complete campaign mission 4
Complete campaign mission 3
Kill 500 enemies
Build 10 turrets
Complete campaign mission 2
Complete campaign mission 1
Kill 50 enemies