Tracking and Data Relay Satellite System

The U.S. Tracking and Data Relay Satellite System (TDRSS, pronounced "T-driss") is a network of American communications satellites (each called a tracking and data relay satellite, TDRS) and ground stations used by NASA for space communications. The system was designed to replace an existing network of ground stations that had supported all of NASA's crewed flight missions. The prime design goal was to increase the time spacecraft were in communication with the ground and improve the amount of data that could be transferred. Many Tracking and Data Relay Satellites were launched in the 1980s and 1990s with the Space Shuttle and made use of the Inertial Upper Stage, a two-stage solid rocket booster developed for the shuttle. Other TDRS were launched by Atlas IIa and Atlas V rockets.

The most recent generation of satellites provides ground reception rates of 6 Mbit/s in the S-band and 800 Mbit/s in the Ku- and Ka-bands. This is mainly used by the United States military.

In 2022 NASA announced that it would gradually phase out the TDRS system and rely on commercial providers of communication satellite services.

To satisfy the requirement for long-duration, highly available space-to-ground communications, NASA created the Spacecraft Tracking and Data Acquisition Network (STADAN) in the early 1960s. Consisting of parabolic dish antennas and telephone switching equipment deployed around the world, the STADAN provided space-to-ground communications for approximately 15 minutes of a 90-minute orbit period. This limited contact-period sufficed for uncrewed spacecraft, but crewed spacecraft require a much higher data collection time.^{[citation needed]}

A side-by-side network established right after STADAN in the early 1960s, called the Manned Space Flight Network (MSFN), interacted with crewed spacecraft in Earth orbit. Another network, the Deep Space Network (DSN), interacted with crewed spacecraft higher than 10,000 miles from Earth, such as the Apollo missions, in addition to its primary mission of data collection from deep space probes.^{[citation needed]}

With the creation of the Space Shuttle in the mid-1970s, a requirement for a higher performance space-based communication system arose. At the end of the Apollo program, NASA realized that MSFN and STADAN had evolved to have similar capabilities and decided to merge the two networks to create the Spacecraft Tracking and Data Network (STDN).

Even after consolidation, STDN had some drawbacks. Since the entire network consisted of ground stations spread around the globe, these sites were vulnerable to the political whims of the host country. In order to maintain a high-reliability rate coupled with higher data transfer speeds, NASA began a study^[when?] to augment the system with space-based communication nodes.

The space segment of the new system would rely upon satellites in geostationary orbit. These satellites, by virtue of their position, could transmit and receive data to lower orbiting satellites and still stay within sight of the ground station. The operational TDRSS constellation would use two satellites, designated TDE and TDW (for east and west), and one on-orbit spare.^{[citation needed]}