Story related and unmissable. On the missions screen on Athena, story missions are marked by a star in the top-right opposite the risk rating. Completing these missions progresses the story and brings you to a point where you can unlock this achievement (details in spoiler).
Story missions do not always appear - you may need to do a regular mission or two before they show up. You'll want to do some non-story missions anyway, to level up and unlock more powerful gear for your crew and ship as you go.