Here is the full list of all 15 Escape From Tethys achievements.
Finish the game in Normal Mode in under 45 minutes.
Find all the ammo upgrades.
Find all the health upgrades.
Explore every area on Tethys.
Find every upgrade.
Unlock the high-security gate.
Finish the game on Normal Mode.
Defeat the IRI Assassin for the last time.
Destroy the missile frigate.
Finish the game on Easy Mode.
Defeat the IRI Assassin for the second time.
Destroy the reef guardians.
Put the rogue scientist to rest.
Defeat the rock creature in the caverns.
Encounter the IRI Assassin.