Here is the full list of all 50 Battle for Orion 2 achievements.
Complete Aristysus by capturing Usama and Theon before the enemy does
Complete campaign mission 3
Complete campaign mission 2
Complete campaign mission 1
Complete campaign mission 4
Complete campaign mission 5
Complete campaign mission 6
Complete campaign mission 7
Complete campaign mission 8
Complete campaign mission 9
Complete campaign mission 10
Complete campaign mission 11
Complete campaign mission 12
Complete campaign mission 13
Complete campaign mission 14
Completed campaign mission 15
Complete campaign mission 16
Complete campaign mission 17
Complete campaign mission 18
Complete campaign mission 19
Complete campaign mission 20
Complete campaign mission 21
Complete campaign mission 22
Complete campaign mission 23
Complete campaign mission 24
Complete Proteus without losing any fighters
Complete Felix In 5 minutes or less
Complete Teuthida without capturing Tastoumia
Complete Caeli without building research modules
Complete Rattus without building turret modules
Complete Odobenus by capturing Niatov last
Complete Pteromyini without letting Zeta group modules get destroyed
Complete Dasyatis in 16 minutes or less
Complete Tadarida without losing any protectors
Complete Unxys without building any tier 2 modules
Complete Apatura before the transport reaches the Pilg system
Complete Caudata without building any tier 2 turrets
Complete Kavose without losing any ships
Complete Cristella without letting Zeta group modules get destroyed
Complete Dynastes by capturing Vas before destroying any transports
Complete Teralyn in 35 minutes or less
Complete Capra after building a fleet of 70 Disrupters
Complete Latonsys by capturing Pictoris last
Complete Phaethon without capturing Formisc or Alarus
Complete Pecari with 9 Executors built
Complete Solice with one of each solar module
Complete Indri with all upgrades maxed
Complete Orion by siding with the Paxor Corporation
Complete Orion by siding with the Kreidge Empire
Complete Orion by siding with the Zeta Group