Hey CptPirx, each race has two campaign missions. Once you've completed the first one it becomes unavailable and the second one takes it's place. The 3 first missions you completed were Leave-6 (Vanguard 01), Arcadia Caeleste (Kir'ko 01) and Chimera Glacialis (Dvar 01) and as you can see you now have three other missions available in their place.