Ha, arnaud, that took everyone a long time. I figured out that I need to race 4 laps well, then turn around on lap 5 through the s curves. There is an arrow right before the weapon pad, so all you need to do is turn around after this, drive over the weapon pad and into the arrow which does not allow you to go over it so you are stuck on the pad until you turn around. Then just fire away. You won't pick up any turbos or autopilots since you are in first place already. You can actually destroy every ship I think, but then you need to boogey to the finish.