Here is the full list of all 22 Orch Star achievements.
Complete the first mission of the campaign
Complete the second mission of the campaign
Complete the third mission of the campaign
Complete the fourth mission of the campaign
Complete the fifth mission of the campaign
Complete the sixth mission of the campaign
Complete the seventh mission of the campaign
Complete the eighth mission of the campaign
Complete the ninth mission of the campaign
Complete the tenth mission of the campaign
Complete the eleventh mission of the campaign
Complete the twelfth mission of the campaign
Rescue the Gray Orchs before the fourth reinforcement wave arrives
Unite with the War Skulls clan, even after attacking them first
Defeat the goblins while each clan has less than 30 ships left
Get to the Tuvali Headquarters within 60 seconds
Stay and defeat all ships at the elven trading post
Defy the Mevorian Empire
Complete a mission after Mevorian reinforcements have been detected
Pursue further understanding of life in space
Control all Techulan stations when capturing the Techulan Core
Complete all optional missions of the campaign