NASA is preparing to launch the second in a series of three, third generation advanced Tracking and Data Relay Satellites, known as TDRS. This latest addition to the fleet of eight, TDRS-L will augment a space communications network that provides the critical path for high data-rate communication to the International Space Station, Hubble Space Telescope, human occupied spacecraft and a host other spacecraft.

Source: “NASA | TDRS: The Network That Enables Exploration”, NASA Goddard, 1/21/2014