saving Ternie - semi spoiler-

[Falcon0]

Well the first thing you should do is pick up a mercanary squadron a system or two back (they hand out around a station).

When you mothership gets disabled you have no choice but to continue with the mission, and your fighters just have to be good enough to clear out the grey forces. First kill all the fighters at the southern base, then head up to the pirate base and trigger the cutscene (you get a new mothership).