You mean the retail star motion blurring effect?
It should work automatically, if the mission background has >0 amount of stars specified.
Since stars are increasingly taken care of with starfield texture instead of retail star system, using zero retail stars will result in the loss of the motion blurring as well. However, there have been vague hints at great things in the future regarding shader system improvements and post-processing, which might lead to introduction of a better motion blur effect that would affect not only stars but other things in motion.
I'll probably not use it though. Never appreciated motion blur, never probably will...
