Tracking and Data Relay Satellites (TDRS) are the largest, most advanced privately developed communications satellites. TDRS provide global coverage of Earth-orbiting spacecraft. In the past, spacecraft could communicate with Earth only when they were in sight of a ground tracking station, typically less than one fifth of the time. The TDRS system enables spacecraft to communicate with Earth for about 85 to 100 percent of the orbit by having a system of orbiting telecommunication satellites operated from a single ground terminal link. The first TDRS was launched from Kennedy Space Center on April 4, 1983. TDRS is owned and operated by the Technical Services Division of Contel Federal Systems, Fairfax, VA. However, its services are being leased to NASA for a ten-year period.