Yeah, I had problems with this one when I replayed it recently too. I managed to finish it by looking for the Vasudan ships visually. I can't exactly describe it, but if you set your speed to zero and look visually around for a group of three dots that look "smoother" than asteroids, that's a wing of Vasudan fighters. Fly towards them, kill them, set speed to zero again and repeat three more times. If you're also looking for the Vasudan Ace, repeat the process one more time but look for a single "smooth" dot instead.
And yeah, I know, this isn't exactly a straightforward or easy solution, but it did get me past this mission.
And if you think this is bad, just wait until you get to "As Lighntning Fall" in FS2. Hoy, that was a bastard and a half to finish! At least there, the flashes of the nav buoys are easier to visually find if you take them one at a time.