After you wake up in the Citadel's clinic, after completing the "Take It Back!" quest, you are greeted by Elder Lyons, who gives a short overview of what happened during the two weeks you have been unconscious. He then sends you to Scribe Rothchild for a more detailed briefing. Rothchild explains how the Brotherhood systematically attacked Enclave camps with the help of Liberty Prime which has proven to be far more effective than expected. The objective of your mission is to learn how the Enclave are still able to communicate and coordinate their scattered forces, even though Raven Rock has been destroyed. It is believed that the Enclave-controlled Satellite Relay Station might be able to provide answers and you are sent there to assist the assault.
When you arrive at Rockland Car Tunnel, you are briefed by Paladin Tristan. As in Take It Back!, Liberty Prime will take point, with you and other Knights providing support. The first phase of the assault proceeds much like that mission, as the giant robot stomps implacably down a canyon, swatting Vertibirds out of the sky and crushing all "Communist" opposition in its path.
When the Brotherhood force arrives at the relay station, Liberty Prime analyzes it for weaknesses and then punches a hole in its wall, allowing entrance. Soon afterward, however, he warns that an uplink transmission has been detected and that an orbital strike is imminent. If you do not stay back or immediately retreat to a safe distance from the robot, you will be killed.
Liberty Prime is wrecked by the missile strike, managing to drag himself only a few yards with his remaining arm before shutting down. In the process, his head comes off; like Deputy Weld's when Megaton is destroyed, it can be activated to hear some of his anti-Communist phrases, now slurred and garbled.
The surviving Brothers regroup, and Tristan orders you to enter the base and find out what just happened. Assisted by a squad of Paladins and Operations Officer Edwards, you must fight through many Enclave soldiers before finally reaching a computer room. Encrypted codes can be downloaded from the mainframe terminal.
You are told to return to the Citadel and give the codes to Scribe Rothchild for further investigation. After lamenting the robot's fate, Rothchild takes the data and directs the player to Elder Lyons. Talking to him finishes Death From Above and starts the next quest, Shock Value.
Source:
http://fallout.wikia.com/wiki/Death_From_Above