This mission is unfinishable. I shoot like 100 hearthbringer bomb and do only 50% damage!!

I've had better luck flying a fighter and keeping the friendly bombers alive long enough.
You should visit Hard Light Productions and download Silent Threat: Reborn. Assuming that you also have FreeSpace 2.

i forget what you had to do in that mission. I remember finisheing but i can't remeber the objectives.

I finally do it take me 1h30 of shotting on a cruiser...