Death From Above

 is a Fallout 3 quest and achievement that is added to the game in the Broken Steel add-on.

Walkthrough
The player is sent to assist a Brotherhood assault on an Enclave outpost at the southwest corner of the map (west of the Dunwich Building), reached via the Rockland Car Tunnel. The Satellite Relay Station is in a new area altogether and is heavily defended by Enclave Soldiers.

Talk to Scribe Rothchild
After you wake up in the Citadel's clinic, you are greeted by Elder Lyons who gives a short overview of what happened during the two weeks you have been passed out and 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.

Meet Paladin Tristan and support him during 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.

Gather data from the Relay Station
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.

Return the data to Scribe Rothchild
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.

Trivia

 * Liberty Prime's death sequence is a reference to the Overseer in Fallout 1; or of a wounded super mutant in a cut scene if the PC sides with the Master at the end of the same. Another possibility is a reference to Frank Horrigan's death who, after being wounded mortally, dragged his upper torso on the ground with his arms before his head blew off.
 * The final moments of Prime also bear a striking resemblance to the finale of The Terminator, in which the Terminator has lost its legs and pursues Sarah Connor by dragging itself with its remaining hand. Liberty is similarly crippled and moves just the same way.

Bugs

 * At the end of Broken Steel Liberty Prime's head can still be found at the Satellite Relay Station despite being in the Citadel at the same time.
 * As of 30 May 09, the achievement "Death From Above" and the 30 points are working on the 360. On the PC, you can fix this by typing into the console "player.setstage XX000802 200", where XX is the load position for Broken Steel.esm.
 * At the beginning, in the room where you wake up, if Sentinel Lyons is alive she'll be 'unconscious' on a bed with no way to interact with her. But if you shoot her with the Gauss Rifle or Victory Rifle and score a critical hit, knocking her down, she will then get up, even though she is completely unconscious.
 * At the end of the mission, should you choose to retrace your steps rather than leave via the roof, all of the dead Enclave soldiers will respawn without their clothing and fire on you.
 * If you haven't completed Picking Up The Trail and instead go straight to Vault 87 sometimes rothchild will bug and not speak about the quest thus you cannot progress.
 * At the beginning you are to speak with scribe Rothchild who then tells you to "go and take a good look at the map". After that he does nothing thus you can not move forward in that quest.The console command "player.setstage XX000802 20" (with XX being the load position for Broken Steel.esm) will bypass this stage of the quest as complete.
 * After Liberty Prime punches a hole in the wall, the door that leads to the next section of the quest is missing. If you attempt to pass through where the door should be, you will fall and be stuck between an invisible wall and the rocks behind the building. The quest marker showing you where to go leads to (what I presume to be) the exit of the quest, north of the original entrance. This occurred whilst using the 1.7 patch.
 * When told to report to Elder Lyons Lyons does not appear in the citadel, but instead the quest marker is way up north, on the right hand side of the river bank, between Bethesda Ruins and Big Town, on the north side of the bridge. - Confirmed on Xbox 360
 * After being briefed by Scribe Rothchild to meet up with Paladin Tristan, you may arrive at the Rockland Car Tunnel only to find the door is locked and requires a key. Go back to the Citadel and speak with Scribe Rothchild again. It will then show you have completed speaking to him (again) and when you go back to Rockland Car Tunnel the door will not be locked. There is no key to obtain. (confirmed on PC)
 * After talking to Rothchild for the mission briefing during Death from Above he will tell you to follow him over to the map. Walk a few feet away from the map and wait until he walks over to it.  Wait about thirty seconds and then talk to him.  He should ask if you have any questions about the Brotherhood.  Be aware that by doing this Rothchild will skip his whole speech about the Enclave encampments they have located.  Your quest will still update with the map marker for Rockland Car Tunnel.  (unconfirmed)