The Tracking and Data Relay Satellite System

The Tracking and Data Relay Satellite System is a communication signal relay system which provides tracking and data acquisition services between spacecraft in low-Earth orbit and spacecraft control, or data processing, facilities.

The TDRSS space segment consists of seven on-orbit Tracking and Data Relay Satellites (TDRSs) located in geosynchronous orbit. The spacecraft constellation is distributed to provide global coverage.

The TDRSS ground segment is located near Las Cruces, New Mexico and consists of two functionally identical ground terminals collectively known as the White Sands Complex. Commands and data for Swift are uplinked from the MOC to the TDRSS and then from the TDRSS to Swift. Return data are downlinked from Swift via the TDRSS to the MOC at PSU.

• TDRSS is used to track the spacecraft and to transmit State of Health telemetry for the spacecraft and its instruments from Swift to the ground.

• TDRSS is used to send burst alert messages to the ground. Swift will be in nearly-constant contact with the TDRSS so that burst alerts can be received when Swift is not in contact with its ground stations. The TDRSS link is used to download BAT localizations of transient sources approximately 12 seconds after initial detection by the BAT, XRT localizations (approximately 90 seconds after the initial detection), and an optical finding chart (approximately 300 seconds after the initial detection).

• TDRSS can also be used to upload commands that allow Swift to observe ToOs. This capability is intended to allow Swift to rapidly observe transients that occur outside the field of view of the BAT, but are detected by other satellites.