Ok Mars/ Exo first, lets move the Exo forward min and take a turn towards the north, however much is required to put its broadside towards the Chaos cruisers. Then bring the Mars just past the Exo and give it a turn towards the north also, same amount. Target the Chaos assault boats with the Mars/ Exo and attempt to destroy them with gunnery fire. Once again any targets that are in range/firearc for the nova should be fired upon (shouldn't be any but could get lucky).
Leave the Dauntless where they are, but move the Retribution up to where it is just slightly closer to the edge of the asteroid field than the southern most Dauntless. That looks like 10-15 cm but its hard to judge. On the Lunars lock on to the Chaos assault boats and move them forward as far as they can go while maintaining arc to the assault boats, you can let them move apart from each other if need be.
Do not launch any ordinance unless the Chaos assault boats are not destroyed by direct fire, if they are not (well there's a lot of really bad rolling going on
) launch only the fighters from the Mars to destroy them.
Move the Imperial assault boats up to just on the Imperial side of the asteroid field, on the Chaos turn if they launch any mixed waves of fighters/bombers or fighters/assault boats go ahead and use the Imperial assault boats to strip as many of the fighters as possible and send any remaining towards the closest Chaos ship. If they launch 6-8 fighters tho attempt to avoid the fighters and attack the closest Chaos ship. Of course if they launch no fighters also attack the closest ship.