Here is the full list of all 31 Space Grunts achievements.
Start a zombie outbreak
Survived the game
Survive the game as Captain
Survive the game as Strongarm
Survive the game as Techjunky
Find and use an anomaly
Find the underground cave
Use the hidden ancients gate
Reach the moonbase
Reach the laboratories levels
Reach the radiation zone levels
Reach the other side
Upgrade shell based weapon to the maximum
Upgrade the frag-based weapon to the max
Upgrade the plasma to the maximum
Survive the Daily Challenge
Collect all datacards
Use the Berzerker
Use the Battle suit
Complete a level without shooting the worms
Unlock the Techjunky b-skin
Unlock the Strongarm B-skin
Unlock the Captain B-skin
Call for reinforcement
Survive the game as B-Captain
Survive the game as B-Strongarm
Survive the game as B-Techjunky
Survive the Worm Dimension
Reach the moonbase in a Daily challenges 30 times
Use Gaia
Escape Zombie attack