When you reach the bunker in the center of the Launch Pad you'll want to head inside and look for the door in the back. Note that several more soldiers will arrive on the Launch Pad via airlift. And when you go through this door into the Satellite Control Tower, you'll have a lot of hostiles point blank.

Fight your way to the Terminal at the top. Here you can use the Terminal to target an orbital strike against the Mobile Crawler. As soon as you have ordered the strike, turn left.

Head out through the door with the yellow claxon. You'll have to pick the lock, but it's not too difficult.

Shortly after you exit onto the deck a Vertibird will land. It does not mean more enemies, rather it's the Brotherhood of Steel coming to pick you up. After a short chat with Sarah, walk over to the Vertibird and hop on board.

After a short ride you'll stop on the roof of the Control Tower to watch the strike against the Mobile Crawler. Once the fireworks are over, hop back on the Vertibird.

Your next stop is the Citadel where Elder Lyons will talk with you for a minute or two. You'll get the quest complete notification after the conversation. You can now talk with Sarah and Rothchild.