The Tracking and Data Relay Satellite System (TDRSS) was declared operational with three (one in the East, one in the West and one spare) Tracking and Data Relay Satellites (TDRS) in geosynchronous orbit (GEO – about 23,000 miles above the Earth) and its ground station in White Sands, New Mexico. Communication coverage for satellites in low Earth orbit (LEO) grew from 15% to over 85% with the three satellites. The remaining 15 percent was referred to as the Zone of Exclusion which was in the middle of the Indian Ocean. By the end of the year, the Spaceflight Tracking and Data Network (STDN) had closed or transferred most its stations; only a handful of sites that supported the Space Shuttle launch and landing were kept open.
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