We have ways of...well you know the rest.
I got the "We have info that the Rebels are planning an offensive, and we want to plan a counter-offensive" mission on Luna, and I've been all over the dad-blasted known galaxy looking for the Rebel Fleet (and even hired a few Kestrel escorts, even though the guy who gave me the mission told me expressly NOT to engage the fleet when I find it, just to see what happens), and haven't found hide nor hair. Apparently I keep raising my reputation in Rebel systems, too, because I'm attacked by at least one or two Pirate Argosies or Corvettes in each system, and I'm not sure if making the Rebels "friendly" is screwing up the mission. For that matter, is the fleet moving around as I do?