A tracking and data relay satellite is a type of communications satellite that forms part of the Tracking and Data Relay Satellite System used by NASA and other United States government agencies for communications to and from independent "User Platforms" such as satellites, balloons, aircraft, the International Space Station, and remote bases like the Amundsen-Scott South Pole Station.

The U.S. (TDRSS, pronounced "T-driss") a network of American communications satellites (each called a tracking and data relay satellite, TDRS) and ground stations used by NASA for space communications.