Im trying to do terran misson 3, "Argon patrol" and its impossible to do with current ship becouse in Omicron Lyrae sys, theres a gang of unbeatable khaak ships. only did storyline missions, did not trade almost anything.

There are quite many X games and a lot of them have the Kha'ak in them. Which game?
Okay, not so many have the Terrans in them. Are you talking about X4?

If something is impossible with the ship you are flying, just get another ship! In these games you are best served by having a fleet, some ships for your personal use and others for remote control.

In X4 there are khaak, but not the sector Omicron Lyrae or terrans. It can't be X4, but there are still 2 games left, X³: Terran Conflict or X³: Albion Prelude.

Albion Prelude not have Khaak's. X-Rebirth have, but only in the sectors of Home of Light DLC, so need to be Terran Conflict.