When the Justice League originally formed, they set up their headquarters inside Mount Justice. Unfortunately, when the team became more public to the world at large, the League's enemies located their base and attacked. As a result, the League was forced to relocate. In order to create a better public image, the League built the Hall of Justice in Washington DC, which would act faux headquarters and public front. In truth, the League designed the orbiting Watchtower as their real base which could be accessed through alien portals.
Watchtower is an orbiting satellite that is the true headquarters of the Justice League. League members are transported to the Watchtower from the Hall of Justice. The Watchtower has sensors that can detect energy surges on the surface of the planet, like the Bialyan desert.