Preparation is the key. Equip ACB-0710 "add back booster" for extra speed, the best non-AA OB you have and two KIKU blades. Make sure your flame is light and speedy, then start the mission. Immediately hit your OB and head for the AF. Supplement your OB with forward QBs if you have enough EN. Once you're close to the AF, blade it anywhere on the structure. If you did it quick enough, the Sol Dios cannons won't have a chance to launch and will be destroyed along with the rest of the AF. It's an S-rank every time.

Source: http://www.trueachievements.com/a25256/af-sol-dios-orbit-achievement.htm