The tracking network includes 31 radar and optical units at 16 sites worldwide. This is the network that the GAO report says can't meet either NASA or defense needs. Debris of all sizes can be dangerous. A paint fleck can gouge a shuttle window. NASA has had to replace more than a dozen shuttle windows in the past few years.
Controllers sometimes have to put spacecraft through an orbital two-step.
Space shuttle crews also have had to duck. During the Hubble telescope repair mission last February, Discovery fired thrusters to avoid an upper-stage rocket fragment from a commercial Pegasus launcher. THE NRC's recent report and a report a year ago on space-station safety each say these strategies aren't good enough. The earlier report calls for more shielding, especially in the poorly protected Russian module. Both reports urge a stronger international effort to minimize creating new debris.