The ADS or Asteroid Detection System is a defense station used for tracking and detecting asteroids. It is made up of an ADS Core Module and 2 ADS Sensor Wings. Starting in sandboxes after mission 20, you will see this (pictured right) setup for the ADS.
Missions regarding the ADS so far are 17, 20, 29.
Mission 17 - ADS Core moved to ADS (waypoint)
Mission 20 - ADS Sensor Wings added
In Mission 29, the ADS module is converted to a manned outpost. A Pod, 2 Large Solar Panels, and a Control Room are added to the ADS module. This is the last mission where you visit the ADS and the last mission to add to an existing space station
In sandbox, a Resupply Module is docked to the core module. The ADS serves no current purpose for sandbox, although the gold color of the Sensors is unique in Space Agency