In the Into The Black campaign, Searchlight is the nickname given to the massive United Nations space station in geosynchronous orbit 30,000km above New London. The nickname is due to the fact that the station appears as a bright star from the ground.
It is roughly 10km long from end to end (much of that distance being massive solar collector arrays), and consists of dozens of apartment-building-sized structures connected by scaffold and "elevator" shafts. It is connected to Eridani Prime by a space elevator on the outskirts of New London. Spaceships are built here, and a substantial portion of the station is spaceport-related.
12,000 people are generally working in the station at any given time.