Mission 18 is a very no-frills level where you pretty much only have to point and shoot. You're immobile, and your turning is slow, but your firepower is vastly better than your regular ship.

The key to completing this level easily is to shoot at your target when its targeting box turns bright yellow momentarily. That indicates that they are within range, and you have a few seconds until they break off and start flying all over the place. Just point squarely in the center of the box, and hold your fire button, and it'll make short work of them.

After the ships with the directional charges come in, make sure to get rid of the Aldebaran ships first, as they're the closest and will break off the earliest. Fire at the cariers constantly, and if a ship comes into range pick it off. Make sure to prioritize the directional charges over the fighters.

If a ship breaks off, ignore it unless no other ships are coming into range. If the ship is going around the edges of your turn area, wait a while for it to come back while working on other targets. The key to getting rid of those ships is to fire ahead of them, not straight at them.