The goal of this mission is to simply protect the freighters until they enter hyperspace (which takes around 13 minutes or more). The key is to intercept or fire missiles at the fighters and bombers, and to press "I" to target any incoming enemy missiles, and shoot them down (for me at least, it's far easier to hit them with lasers than with missiles). But you can't get too close to the enemy capital ship, which is armed to the teeth.
