Here is the full list of all 26 Outpost: Infinity Siege achievements.
Save a missing operative.
Defeat a Bomber using melee.
Complete 100 Recovery Days.
Explore 10 different landmarks.
Defeat Crius for the first time.
Complete all research projects.
Have a single round cost of more than 150.
Reach an Outpost value of 100000.
Clear level [Seraph] for the first time.
Exploit Kronos' weakness and make him kneel down.
Defeat Kronos for the first time.
Do not touch the ground for more than 30 seconds.
Defeat 5000 enemies by hitting the weak spot.
Complete recovery after 15 Exploration Days.
Reach an Outpost value of 50000.
Clear level [The Nebulas] for the first time.
Reach level 30.
Unlock all departments.
Clear level [Rescue] for the first time.
Reach an Outpost value of 10000.
Recover items worth 3000R in a single Recovery.
Open a locked container using a lockpick.
Run at the human speed limit.
Clear level [Outpost 11] for the first time.
Deal more than 5000 damage in a single instance.
Clear level [Into the Abyss] for the first time.