I'm guessing you're not a fan of the Scimitar. This is my favorite Scim mission (Bifrost 2). Since the Salthi and Krant shouldn't give you trouble, so just use your Mass Drivers. Use your two dumbfires against the Jalthis' rear armor. With the Jalthi gone, use your HSs close in against the Gratha, when they arrive. Use your limited gun power well, and your mass drivers will get the job done.