Here is the full list of all 30 Gemini Wars achievements.
Defended Saruni system from an Alliance offensive
Helped the USF forces on Korvus
Destroyed the Alliance forces on Giomos
Protected Dogar Prime's evacuation
Meet Admiral Ragnar
Defeated the Gark at Quelatrix
Protected Galileu's scientific teams
Used an orbital super cannon
Destroyed Roarke's stronghold
Boarded a Gark station
Completed the infiltration mission on Ngaxu
Rescued Admiral Robertz
Protected the wounded on Heromon
Destroyed the Gark Planet Destroyer
Destroyed the Gark Stargate
Complete the Gemini Campaign
Destroy 100 enemy ships
Destroy 500 enemy ships
Destroy 1000 enemy ships
Control 10 Fighter squadrons
Train 150.000 marines in a single mission
Build 10 colonies
Controls 5 Battlesihips at the same time
Extract 100.000 Crystals
Extract 500.000 Crystals
Destroy 5 Colonies
Destroy 100 Gark Ships
Destroy 500 Gark ships
Use a battleship special ability
Build 100 Heavy Turrets