Tracking and Data Relay Satellites (TDRS)

Quick facts

Overview

Summary

Mission Capabilities

The Tracking and Data Relay Satellite System (TDRSS) provides data relay services to NASA and NASA partner satellite missions. To achieve this, each TDRS flight unit carries two single-access (SA) antennas, one multi-access (MA) antenna array, a space-to-ground link (SGL) antenna, and an omni-antenna. The first-generation single access antennas operated in S-band and Ku-band, while the second and third both operate in S-band, Ku-band and Ka-band. All generations of multi-access antennas include a diplexed element for dual transmit and receiving functions, and have a ±13° field of view.

Performance Specifications

The third and most modern generation of TDRS provides SA antenna data rates of up to 23.6 Mbps for return and 14 Mbps for forward data. The Ku-band provides up to 600 Mbps for return and 50 Mbps forward, while the 225 MHz and 650 MHz Ka-bands provide up to 600 Mbps and 1200 Mbps return, respectively. Both Ka-bands provide 50 Mbps forward data. The MA antenna array provides a data rate of up to 7 Mbps for return and 3 Mbps for forward data.

All TDRS satellites operate in geostationary orbit, with the three primary satellites positioned to provide global coverage, and the remainder acting as on-orbit backups for redundancy.

Space and Hardware Components

The first-generation of TDRS used a TRW Aeronautical Systems bus, measuring 17.4 m x 14.2 m on the horizontal plane, with a launch mass of approximately 2100 kg. For power generation, the bus carried two solar arrays with a total area of 29 m2, as well as two 40 Ah nickel-cadmium batteries to provide power during eclipse. The second and third generation TDRS both used the Boeing 601 satellite bus, measuring 2.7 m x 3.2 m x 4.3 m without solar panels, and with a launch mass of 3196 kg. The spacecraft has two bus-mounted silicon solar arrays, providing up to 2300 W of power, with nickel-hydrogen batteries supplying spacecraft power during solar eclipses.

Overview

The NASA Tracking and Data Relay Satellites (TDRS) are the satellite component of the Tracking and Data Relay Satellite System (TDRSS), a space-based communication relay system providing tracking and data acquisition services between satellites in Low Earth Orbit (LEO) and ground-based data processing or spacecraft control facilities. Satellites transmit information to one of three active TDRS units, which relay the transmission to ground stations. TDRSS provides this service to more than 25 active satellite missions, including the Hubble Space Telescope and the International Space Station.

Prior to TDRS, NASA’s ground-based satellite communications network only provided coverage for approximately 15% of a satellite’s orbit. With the introduction of TDRS, this has been increased to nearly 95%, where high-latitude regions are not fully covered due to geosynchronous orbits used by TDRSS. There are three generations of TDRS satellites, with the first consisting of TDRS-A through -F, the second of -H, -I and -J, and the third with -K, -L, and -M. The first satellite, TDRS-A, was launched in April 1983. 1) 2) 3) 6)

Of the 13 satellites in the programme, six are operational as of 2026: TDRS-F and -G from the first generation, TDRS-H from the second generation, and all three third-generation satellites (TDRS-K, -L and -M). As the constellation operates in geosynchronous orbit, only three satellites are required to provide near-global coverage. This service is provided by the three third generation spacecraft, with the remaining four serving as on-orbit spares in the event of a failure. The entire TDRSS or Space Network (SN) consists of the TDRS space component, two colocated ground terminals at NASA’s White Sands Complex (WSC) in New Mexico, remote extensions in Guam and Blossom Point, Maryland, as well as a contingency Telemetry, Tracking and Command (TT&C) station in Alice Springs, Australia. 4) 5) 6)

Spacecraft 

First Generation

The first generation of TDRS uses a TRW Aeronautical Systems bus, specifically constructed for the data relay satellite system. The spacecraft measures 17.4 m x 14.2 m on the horizontal plane, with a launch mass of approximately 2100 kg. The electrical power subsystem consists of two solar arrays with a total area of 29 m2, providing 2 kW of beginning-of-life (BOL) power generation and 1.7 kW at end-of-life (EOL), as well as two 40 Ah nickel-cadmium batteries to provide power during eclipse. The attitude control system (ACS) uses momentum wheels and Earth sensors, and the bus houses a hydrazine propulsion system with 24 4.5 N thrusters. 7) 8)

Second Generation

The second generation of TDRS uses the Boeing BSS-601 satellite platform. The spacecraft bus, excluding solar panels, has dimensions 2.7 m x 3.2 m x 4.3 m, with a launch mass of 3196 kg. Each BSS-601 platform consists of two modules, with the first holding launch vehicle loads and the propulsion system, and the second housing communications equipment, electronics and battery systems, and isothermal heat pipes. Solar arrays, as well as the mission antenna and reflector package, are mounted on the first module. The BSS-601 bus for the second generation of TDRS uses an electronic propulsion system, the Xenon Ionic Propulsion System (XIPS), which reduces the required propellant mass by 90% compared to chemical propellant systems. BSS-601 uses the 13 cm XIPS model which provides 18 mN of thrust and 2350 s of specific impulse, operating at 450 W. The spacecraft has two bus-mounted silicon solar arrays, providing up to 2300 W of power, with nickel-hydrogen batteries supplying spacecraft power during solar eclipses. 7) 9) 10)

Third Generation

The three third-generation TDRS use a near-identical Boeing 601 bus to the second generation models, with the only significant change being the relocation of the Multiple Access Return (MAR) beamformer. 7)

Launches

All TDRSS flight units operate from geosynchronous orbit, at an altitude of 35,786 km. With the beginning of the second generation, TDRS used Atlas II and V rockets, as opposed to the Challenger Space Shuttles used to launch the first generation satellites.

Mission Status

• April 10, 2026: NASA issued a draft solicitation for Project NEXUS, which aims to develop a commercially owned Ka-band satellite relay service to replace TDRS. NASA is in the process of gradually retiring TDRSS and moving new missions to commercial communications services. 27)
• August 13, 2024: NASA’s Flight Dynamics Facility (FDF) successfully completed a series of end of mission operations for TDRS-J. The procedure consisted of orbital manoeuvres and fuel depletion operations, in preparation for the satellite’s deorbiting. 26)
• January 5, 2023: TDRS-I, the ninth spacecraft of the programme, was retired after surpassing its 15-year life expectancy. The satellite had been experiencing intermittent connectivity issues since August 2022, and an assessment concluded that it would not be able to continue relaying data reliably. 12)

• January 13, 2013: The first third generation TDRS unit was successfully launched from the Cape Canaveral launch facility in Florida. The launch used an Atlas V rocket.
• May 1, 2012: TDRS-D, after 23 years in orbit, was passivated and turned off. The satellite had well exceeded its original 10-year life expectancy, and one of its three batteries had failed, with the other two experiencing reduced capacity. 13)
• June 27, 2010: TDRS-A, the first spacecraft of the TDRS programme, was retired after 27 years of service. Decommissioning started on June 5, 2010, with passivation completed on June 27. TDRS-C was repositioned to replace TDRS-A. 14)
• June 30, 2000: The first of the TDRS second-generation satellites, TDRS-H, was successfully launched using an Atlas IIA launch vehicle from NASA’s Cape Canaveral facility in Florida. 2)
• February 23, 1995: NASA’s Goddard Space Flight Centre selected Boeing Systems to build three next-generation TDRS satellites to replace the ageing first-generation constellation. The contract was valued at USD $481.6 million and included the upgrade of the two TDRS ground stations at White Sands, New Mexico. 18)
• January 28, 1986: TDRS-B was destroyed in the launch failure of the STS-51-L mission, the final launch of the Space Shuttle Challenger. The disaster resulted in the deaths of the seven crew members of the shuttle, 73 seconds after liftoff. An investigation attributed the disaster to an O-ring failure in the right solid rocket booster, aggravated by extreme cold conditions in Florida. 11)

• April 4, 1983: TDRS-A, the first satellite of the programme, was successfully launched from the Kennedy Space Centre aboard the Space Shuttle Challenger STS-6 mission. The second solid rocket motor used by the Inertial Upper Stage (IUS) suffered an attitude control failure, resulting in TDRS-A being released into a lower orbit than initially planned. However, it was eventually raised into its planned geosynchronous orbit using the onboard attitude control system. This adjustment resulted in a higher inclination orbit than originally planned, which allowed the spacecraft to cover higher latitudes. 5) 14)

Sensor Complement

All three generations of TDRS carry a combination of single-access (SA), multiple-access (MA), and space-to-ground link (SGL) antennas.

First Generation TDRS Antenna Package

The first generation includes two SA antennas, one MA antenna array, one SGL antenna and one omni-antenna.

Each of the SA antennas is a 4.9 m-diameter molybdenum wire mesh antenna, used for Ku-band and S-band links, and capable of left or right-hand circular polarisation. These are two-axis steerable, and can communicate with a single spacecraft at a time. These antennas provide data rates of up to 23.6 Mbps for return and 14 Mbps for forward data in S-band, and up to 600 Mbps return or 50 Mbps forward in Ku-band. They have a rectangular field of view covering ±22° E-W and ±28° N-S. 15) 16) 17)

The MA Antenna Array is an S-band phased array consisting of 30 fixed helix antennas and is electronically steerable. Twelve of these helices are diplexed for transmission, while the rest can only receive. The array can receive data from up to 20 spacecraft at a time, and transmit to just one. The first-generation TDRS MA system provides data rates of up to 525 Kbps for return and 300 Kbps for forward data. The array has a ±13° conical field of view. 15) 16) 17)

The SGL Antenna is a 2 m parabolic antenna operating in Ku-band, providing the communications link between the TDRS satellites and the ground. The SGL antennas are perpendicular linear polarised, and used for all customer data as well as TDRS tracking, telemetry and control (TT&C) signals. Each antenna is two-axis gimballed. 15) 16)

The Omni-Antenna is a conical log spiral used solely during the deployment phase and as a backup in case of emergency. This antenna operates in S-band. 15) 16)

Second and Third Generation TDRS Antenna Package

The second and third generations also include two SA antennas, one MA antenna array, one SGL antenna and one omni-antenna.

The  SA Antennas are pointable 4.9 m-diameter graphite mesh reflectors providing tri-frequency communications in S-, Ku-, and Ka-band, with left- or right-hand circular polarisation. 17) 18) 19) 20)

The second- and third-generation MA array consists of 32 receive antenna elements, with 15 diplexed for transmitting. The MA array operates in S-band between 2.0-2.3 GHz with left-hand circular polarisation and a ±13° field of view. Beamforming is done onboard by the spacecraft, and the array provides a data rate of up to 7 Mbps for return and 3 Mbps for forward data. 17) 18) 19) 20)

The SGL Antenna is a 2.4 m Ku-band antenna, with perpendicular linear polarisation, providing a ground station link for TDRS satellites. The second and third generations of TDRS use a modified frequency plan for the SGL antennas. 18) 19) 20)

The second and third generations also carry a single conical log spiral omni-antenna, operating in S-band and used as a backup and for TT&C during deployment. 18) 19) 20)

Ground Segment

The TDRS ground segment primarily consists of the control station and data processing facility at White Sands, New Mexico, which houses two colocated ground terminals, the White Sands Ground Terminal (WSGT) and the Second TDRSS Ground Terminal (STGT), located 3 km to the North. STGT was opened in April 1994 as a backup to WSGT, to ensure continuous service in the event of outages or planned servicing. The ground segment also has remote extensions in Guam and Blossom Point, Maryland, as well as a contingency Telemetry, Tracking and Command (TT&C) station in Alice Springs, Australia.

From 2025 to 2027, the White Sands facility has undergone a series of upgrades under the Space Network Ground Segment Sustainment (SGSS) programme, with General Dynamics as the key contractor. SGSS entails the modernisation of the White Sands ground station and the Terminal at the Guam Remote Station, as well as the construction of a third ground station at Blossom Point, Maryland. This modernisation process will overhaul the architecture and function of the TDRS ground station while retaining some existing hardware, including the three 18.3 m dish antennas at the White Sands complex. 21) 22) 23) 24) 25)

References  

1) Gunter’s Space Page, “TDRS 1, 2, 3, 4, 5, 6”, URL: https://space.skyrocket.de/doc_sdat/tdrs-1.htm

2) Gunter’s Space Page, “TDRS 8, 9, 10”, URL: https://space.skyrocket.de/doc_sdat/tdrs-8.htm

3) Gunter’s Space Page, “TDRS 11, 12, 13”, URL: https://space.skyrocket.de/doc_sdat/tdrs-11.htm

4) Spaceflight Now, “The TDRS-J Satellite”, URL: https://www.spaceflightnow.com/atlas/ac144/021201tdrs.html

5) NASA, “Tracking and Data Relay Satellites”, URL: https://www.nasa.gov/missions/tdrs/tracking-and-data-relay-satellite-tdrs-generations-of-spacecraft/

6) NASA, “TDRS: Continuing the Critical Lifeline”, URL: https://www.nasa.gov/wp-content/uploads/2022/04/tdrsfactsheet_3.pdf?emrc=6963433c6aab5

7) NASA, “Tracking and Data Relay Satellite (TDRS) Characteristics”, URL: https://web.archive.org/web/20210408025455/https://www.nasa.gov/directorates/heo/scan/services/networks/tdrs_characteristics

8) Astronautix, “TDRS”, URL: http://www.astronautix.com/t/tdrs.html

9) Space Systems Forecast, “Boeing-601”, URL: https://www.forecastinternational.com/archive/disp_pdf.cfm?DACH_RECNO=306

10) William G. Tighe et al., “XIPS Small Ion Thrusters for Small Satellite Applications”, URL: https://digitalcommons.usu.edu/cgi/viewcontent.cgi?params=/context/smallsat/article/1459/&path_info=SSC07_III_11.pdf

11) NASA, “STS-51-L”, URL: https://www.nasa.gov/mission/sts-51l/

12) NASA, “NASA’s Tracking and Data Relay Satellite-9 Reaches End of Mission”, URL: https://www.nasa.gov/general/nasas-tracking-and-data-relay-satellite-9-reaches-end-of-mission/

13) NASA, “Tracking and Data Relay Satellite 4 (TDRS-4) Retired”, URL: https://www.nasa.gov/image-article/may-2012-tracking-data-relay-satellite-4-tdrs-4-retired/

14) NASA, “NASA Retires First Data Relay Satellite After Stellar Career”, URL: https://web.archive.org/web/20161226145727/https://www.nasa.gov/home/hqnews/2010/jun/10-154_TDRS_Retirement.html

15) NASA, “Tracking and Data Relay Satellite (TDRS) First Generation Capabilities”, URL: https://web.archive.org/web/20211020060808/https://www.nasa.gov/directorates/heo/scan/services/networks/tdrs_first_gen

16) P.B. Phung et al., “Tracking and Data Relay Satellite System (TDRSS) Range and Doppler Tracking System Observation Measurement and Modeling”, URL: https://ntrs.nasa.gov/api/citations/20180003065/downloads/20180003065.pdf

17) NASA, “Three Generations of Tracking and Data Relay Satellite (TDRS) Spacecraft”, URL: https://ntrs.nasa.gov/api/citations/20160007352/downloads/20160007352.pdf

18) NASA, “Three Newly Designed Tracking and Data Relay Satellites To Help Replenish Existing On-Orbit Fleet”, URL: https://web.archive.org/web/20090319003124/http://www.nasa.gov/centers/goddard/pdf/97440main_TDRS_fs_9.18.pdf

19) NASA, “Tracking and Data Relay Satellite (TDRS) Second Generation Capabilities”, URL: https://web.archive.org/web/20211011051847/https://www.nasa.gov/directorates/heo/scan/services/networks/tdrs_second_gen

20) NASA, “Tracking and Data Relay Satellite (TDRS) Third Generation Capabilities”, URL: https://web.archive.org/web/20200208014952/https://www.nasa.gov/directorates/heo/scan/services/networks/tdrs_third_gen

21) SpectrumWiki, “NASA Tracking and Data Relay Satellite System (TDRSS)”, URL: https://www.spectrumwiki.com/wiki/DisplayEntry.aspx?DisplyId=233

22) General Dynamics Mission Systems, “Space Network Ground Segment Sustainment (SGSS)”, URL: https://gdmissionsystems.com/satellite-ground-systems/space-network-ground-segment-sustainment

23) General Dynamics Mission Systems, “Tracking and Data Relay Satellite System (TDRS)”, URL: https://gdmissionsystems.com/satellite-ground-systems/tracking-and-data-relay-satellite-system

24) J. Donaldson et al., “Commissioning of NASA’s 3rd Generation Tracking and Data Relay Satellites (TDRS KLM)”, URL: https://arc.aiaa.org/doi/pdf/10.2514/6.2018-2359

25) NASA, “The Tracking and Data Relay Satellite System”, URL: https://ntrs.nasa.gov/api/citations/19870000738/downloads/19870000738.pdf

26) NASA, “NASA’s Flight Dynamics Facility Completes Critical End-of-Mission Operations for TDRS-10”, URL: https://web.archive.org/web/20260316213428/https://etd.gsfc.nasa.gov/etd-featured-stories/nasas-flight-dynamics-facility-completes-critical-end-of-mission-operations-for-tdrs-10/

27) SpaceNews, “NASA seeks proposals for commercial TDRSS replacement”, URL: https://spacenews.com/nasa-seeks-proposals-for-commercial-tdrss-replacement/