NASA's early system of tracking satellites in Earth orbit. STDN, operated by the Goddard Space Flight Center (GSFC), established 14 telecommunications ground stations around the world for tracking, although this covered only 14% of a satellite's orbit. Data collected by the stations was relayed to Goddard. STDN was superseded by the Tracking and Data-Relay Satellite (TDRS) system that provides a coverage of 85–100%.