For tracking purposes, there are two types of space objects—cooperating and noncooperating. Normal civilian satellites and some military satellites use beacons and radar reflectors to assist ground stations in keeping track of satellite locations. Beacons are transmitters that broadcast a simple radio signal that, in essence, tells the Earth-based tracking radar, "Here I am. Here I am. Here I am." Radar reflectors are simply the normal parts of satellites that effectively reflect the radar signal. Examples of radar reflectors are solar panels and heat radiators.

Flight controllers monitor pre-docking operations between the space shuttle Atlantis and the International Space Station at the Mission Control Center in Houston.

How Objects Are Tracked

The U.S. Space Command has primary responsibility for keeping track of everything in orbit. Information from radars, optical systems, and space-based sensors are integrated by the Space Control Center, which is...