If you are trying for an "S" rank, take the time to use Allied Attack and Cover to take out some of the UAVs that Pasternak uses to attack you and your squadron. After you have killed about five of the UAVs, concentrate your fire on Pasternak. He is always visible with ESM. This should give you an advantage. Later his ESM will disappear. Pay attention to your radar and use the Right Analog-stick to look around for him. If you are not trying for an "S" rank, use Allied Attacks directly on Pasternak so that your squadron keeps him busy while you take the shots on him. He always stops to fire his ADMMs; use that as an advantage to your Allied Attacks and missile attacks.