In a mission of Freespace 2, I'm asked to destroy all four of the Sathanas' beam turrets before it engages its subspace drives to go attack the Colossus. This is very difficult. Even when I constantly fire both guns at the tips of the turrets and use up all of both my Helios and other missiles, I'm only able to destroy at most three of them, and this is heavily dependent on whether or not my Helios missiles do 30% damage or 87% damage, influenced by a factor I do not understand. Is there something I'm missing here? How do I destroy all four of these beam turrets, and how do I inflict maximum damage with my Helios missiles to ensure this happens?
Step 1) Call for a rearm ship right away so it follows you around for reload.
Step 2) Fly at the Sathanas so it is moving towards you, however stay on the outside of the ship, flying to the front-centre will get you hit with the flak guns.
Step 3) A double Helios shot will take out the turrets, or bring them low. Follow up with your Trebs
Step 4) Fly away from the Sathanas towards the jump node, turn around, do it again.
Step 5) Stop, let the rearm ship refuel you, when it is done call for a rearm again just in case.
Step 6) Keep doing this over and over, you should be able to take out all four. However, only two are required to complete the mission.
Step 7) You'll be asked to destroy extra turrets on the Sathanas, this doesn't carry over to the next mission, so instead just get clear of the Sathanas so you don't get hit when it jumps.
After that, rearm again as a Demon-class destroyer comes in to play, I'll let the mission tell you the rest.
If I remember correctly, those turrets require double helios missles to kill. What you should do is dive straight at it with afterburners on, shoot off double missiles, then pull out. Before making a second run, make a call for a resupply ship as you make a run at the second turret. After taking care of that one, immediately resupply (as the ship should be following you at that point), and attack the last two turrets.
The Sathanas mounts a pair of long range flak on a ledge on the front "face" of the ship. Due to the trajectory of the Trebuchets, dual Trebs don't really impact correctly to kill them off. Others may have better luck.
The long range flak are not really damaging (DPS wise). Divert more energy to the shields and they won't cause much problems. (the resupply ship may have greater problems though!)
IIRC, there is LRed beam at the rear of the ship, which you can take out if you have time (HLP people claim it is possible).