TDRS Program LogoLocation of TDRS as of March 2019An unflown TDRS on display at the Steven F. Udvar-Hazy Center in Chantilly, Virginia.
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 6Mbit/s in the S-band and 800Mbit/s in the Ku- and Ka-bands. This is mainly used by the United States military.[1]
In 2022 NASA announced that it would gradually phase out the TDRS system and rely on commercial providers of communication satellite services.[2]
Origins
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]
After the study was completed, NASA realized that a minor system modification was needed to achieve 100% global coverage. A small area would not be within line-of-sight of any satellites – a so-called Zone of Exclusion (ZOE). With the ZOE, neither TDRS satellite could contact a spacecraft under a certain altitude (646 nautical miles). With the addition of another satellite to cover the ZOE and ground station nearby, 100% coverage could exist. The space-based network study created a system that became the plan for the present-day TDRSS network design.[3]
As early as the 1960s, NASA's Application Technology Satellite (ATS) and Advanced Communications Technology Satellite (ACTS) programs prototyped many of the technologies used on TDRSS and other commercial communications satellites, including frequency division multiple-access (FDMA), three-axis spacecraft stabilization and high-performance communications technologies.[citation needed]
As of July2009[update], TDRS project manager is Jeff J. Gramling, NASA Goddard Space Flight Center.[4] Robert P. Buchanan, Deputy Project Manager, retired after 41 years at NASA with TDRS as one of final missions. Boeing is responsible for the construction of TDRS K.[5]
The network
TDRSS is similar to most other space systems, whereby it is composed of three segments: the ground, space and user segments. These three segments work in conjunction to accomplish the mission. An emergency or failure in any one segment could have catastrophic impact on the rest of the system. For this reason all segments have redundancy factored in.
Additionally, the WSC remotely controls the GRGT on Guam.
The WSC has its own exit from U.S. Route 70 that is for facility staff only. NASA decided on the location of the ground terminals using very specific criteria. Foremost was the ground station's view of the satellites; the location had to be close enough to the equator to view the skies, both east and west. Weather was another important factor – New Mexico has, on average, almost 350 days of sunshine per year, with a very low precipitation level.
WSGT went online with the 1983 launch of TDRS-A by the Space Shuttle Challenger. STGT became operational in 1994, completing the system after Flight-6's on-orbit checkout earlier in the year. Additionally, after completion of the second terminal, NASA held a contest to name the two stations. Local middle school students chose Cacique (kah-see-keh), meaning leader for WSGT, and Danzante meaning dancer for STGT. These names seem to have been for publicity purposes only, for official NASA documentation use WSGT and STGT or WSC as designators.
WSGT and STGT are geographically separated and completely independent of one another, while retaining a backup fiber-optic link to transfer data between sites in case of emergency. Each ground station has 19-meter dishes, known as Space-Ground Link Terminals (SGLT), to communicate with the satellites. Three SGLTs are located at STGT, but only two are located at WSGT. The system architects moved the remaining SGLT to Guam to provide full network support for the satellite covering the ZOE. Considered a remote part of the WSGT, the distance and location of the SGLT is transparent to network users.
The Guam Remote Ground Terminal (GRGT) 13°36′53″N144°51′23″E / 13.6148°N 144.8565°E / 13.6148; 144.8565 is an extension of the WSGT. The terminal contains SGLT 6, with the Communication Service Controller (CSC) located at STGT's TDRS Operations Control Center (TOCC). Before the GRGT was operational, an auxiliary system was located at Diego Garcia.
NISN provides the data transfer backbone for space missions. It is a cost-effect wide area network telecommunications service for transmission of data, video, and voice for all NASA enterprises, programs and centers. This part of the STDN consists of infrastructure and computers dedicated to monitor network traffic flow, such as fiber optic links, routers and switches. Data can flow through NISN two ways: using the Internet Protocol Operational Network (IPONET) or the High Data Rate System (HDRS). IPONET uses the TCP/IP protocol common to all computers connected to the Internet, and is a standard way to ship data. The High Data Rate System transports data rates from 2Mbit/s to48Mbit/s, for specialized missions requiring a high rate of data transfer. HDRS does not require the infrastructure of routers, switches and gateways to send its data forward like IPONET.
The NCC provides service planning, control, assurance and accountability. Service planning takes user requests and disseminates the information to the appropriate SN elements. Service control and assurance supports functions of real-time usage, such as receipt, validation, display and dissemination of TDRSS performance data. Service accountability provides accounting reports on the use of the NCC and network resources. The NCC was originally located at Goddard Space-flight Center, in Greenbelt, Maryland until 2000, when it was relocated to the WSC.
The MOC is the focal point of spacecraft operations. It will schedule requests for support, monitor spacecraft performance and upload control information to the spacecraft (through TDRSS). MOC consists of principal investigators, mission planners and flight operators. Principal investigators initiate requests for SN support. Mission planners provide documentation for the spacecraft and its mission. And flight operators are the final link, sending commands to the spacecraft and performing the operations.
The MMFD lab provides flight project and tracking network support. Flight project support consists of orbital and attitude determination and control. Orbital parameters are traced through the actual orbit of the mission spacecraft and compared to its predicted orbit. Attitude determination computes sets of parameters that describe a spacecraft's orientation relative to known objects (Sun, Moon, stars or Earth's magnetic field). Tracking network support analyzes and evaluates the quality of the tracking data.
Space segment
TDRSS satellite
The space segment of the TDRSS constellation is the most dynamic part of the system. Even with nine satellites on orbit, the system provides support with three primary satellites, while using the rest as on-orbit spares capable of immediate usage as primaries. The original TDRSS design had two primary satellites, designated TDE, for east, and TDW, for west and one on-orbit spare. The surge in user requirements during the 1980s allowed NASA to expand the network with the addition of more satellites, with some being co-located in a particularly busy orbital slot. See Tracking and Data Relay Satellite for more details on the satellites.
User segment
The user segment of TDRSS includes many of NASA's most prominent programs. Programs such as the Hubble Space Telescope and LANDSAT relay their observations to their respective mission control centers through TDRSS. Since crewed space flight was one of the primary reasons for building TDRSS, the space shuttle and International Space Station voice communications are routed through the system.
Operations
South Pole Tracking Relay-2
The TDRSS system has been used to provide data relay services to many orbiting observatories, and also to Antarctic facilities such as McMurdo Station by way of the TDRSS South Pole Relay. The US-built sections of the International Space Station (ISS) use TDRSS for data relay. TDRSS is also used to provide launch data relay for expendable boosters.[which?]
Military applications
As early as 1989, it was reported that an important function of TDRSS was to provide data relay for the Lacrosse radar imaging reconnaissance satellites operated by the National Reconnaissance Office.[8]
Almost twenty years later, on November 23, 2007, an on-line trade publication noted, "While NASA uses the (TDRSS) satellites to communicate with the space shuttle and international space station, most of their bandwidth is devoted to the Pentagon, which covers the lion's share of TDRSS operations costs and is driving many of the system's requirements, some of them classified."[9]
Note: while a TDRSS satellite is in the manufacturing process it is given a letter designation, but once it has successfully achieved the correct geosynchronous orbit it is referred to with a number (for example, TDRS-A during development and before on-orbit acceptance, and TDRS-1 after acceptance on orbit and put into operational use). Thus, satellites that are lost in launch failures or have massive malfunctions are never numbered (for example, TDRS-B, which was never numbered due to its loss in the Space Shuttle Challenger disaster).
A spacecraft is a vehicle that is designed to fly and operate in outer space. Spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, planetary exploration, and transportation of humans and cargo. All spacecraft except single-stage-to-orbit vehicles cannot get into space on their own, and require a launch vehicle.
STS-8 was the eighth NASA Space Shuttle mission and the third flight of the Space Shuttle Challenger. It launched on August 30, 1983, and landed on September 5, 1983, conducting the first night launch and night landing of the Space Shuttle program. It also carried the first African-American astronaut, Guion Bluford. The mission successfully achieved all of its planned research objectives, but was marred by the subsequent discovery that a solid-fuel rocket booster had almost malfunctioned catastrophically during the launch.
STS-26 was the 26th NASA Space Shuttle mission and the seventh flight of the orbiter Discovery. The mission launched from Kennedy Space Center, Florida, on September 29, 1988, and landed four days later on October 3, 1988. STS-26 was declared the "Return to Flight" mission, being the first mission after the Space Shuttle Challenger disaster of January 28, 1986. It was the first mission since STS-9 to use the original Space Transportation System (STS) numbering system, the first to have all its crew members wear pressure suits for launch and landing since STS-4, and the first mission with bailout capacity since STS-4. STS-26 was also the first U.S. space mission with an all-veteran crew since Apollo 11, with all of its crew members having flown at least one prior mission.
STS-43, the ninth mission for Space Shuttle Atlantis, was a nine-day mission whose primary goal was launching the TDRS-E satellite (TDRS-5). The flight also tested an advanced heatpipe radiator for potential use on the then-future space station and conducted a variety of medical and materials science investigations.
Landsat 4 is the fourth satellite of the Landsat program. It was launched on July 16, 1982, with the primary goal of providing a global archive of satellite imagery. Although the Landsat Program is managed by NASA, data from Landsat 4 was collected and distributed by the U.S. Geological Survey. Landsat 4 science operations ended on December 14, 1993, when the satellite lost its ability to transmit science data, far beyond its designed life expectancy of five years. The satellite housekeeping telemetry and tracking continued to be maintained by NASA until it was decommissioned on June 15, 2001.
A tracking and data relay satellite (TDRS) is a type of communications satellite that forms part of the Tracking and Data Relay Satellite System (TDRSS) 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. This system was designed to replace an existing worldwide network of ground stations that had supported all of NASA's crewed flight missions and uncrewed satellites in low-Earth orbits. The primary system design goal was to increase the amount of time that these spacecraft were in communication with the ground and improve the amount of data that could be transferred. These TDRSS satellites are all designed and built to be launched to and function in geosynchronous orbit, 35,786 km (22,236 mi) above the surface of the Earth.
The Inertial Upper Stage (IUS), originally designated the Interim Upper Stage, was a two-stage, solid-fueled space launch system developed by Boeing for the United States Air Force beginning in 1976 for raising payloads from low Earth orbit to higher orbits or interplanetary trajectories following launch aboard a Titan 34D or Titan IV rocket as its upper stage, or from the payload bay of the Space Shuttle as a space tug.
The Manned Space Flight Network was a set of tracking stations built to support the American Mercury, Gemini, Apollo, and Skylab space programs.
Space Network (SN) is a NASA program that combines space and ground elements to support spacecraft communications in Earth vicinity. The SN Project Office at Goddard Space Flight Center (GSFC) manages the SN, which consists of:
The Near Earth Network provides orbital communications support for near-Earth orbiting customer platforms via various ground stations, operated by NASA and other space agencies. It uses a number of different dishes scattered around the globe. The antennas must be able to move fast for tracking of objects in low Earth orbit (LEO). The NEN and Space Network (SN) combined were previously referred to as the Spaceflight Tracking and Data Network (STDN).
TDRS-B was an American communications satellite, of first generation, which was to have formed part of the Tracking and Data Relay Satellite System. It was destroyed in 1986 when the Space ShuttleChallenger disintegrated 73 seconds after launch.
TDRS-1, known before launch as TDRS-A, was an American communications satellite, operated by NASA as part of the Tracking and Data Relay Satellite System. It was constructed by TRW and launched by Space ShuttleChallenger on its maiden flight, STS-6.
The Merritt Island Spaceflight Tracking and Data Network station, known in NASA parlance as MILA, was a radio communications and spacecraft tracking complex located on 61 acres (0.25 km2) at the Kennedy Space Center (KSC) in Florida. The name MILA was an acronym for the "Merritt Island Launch Annex" to Cape Canaveral Air Force Station, which was how the site was referred to when spacecraft launches were primarily originating from the adjacent military installation. MILA's arrays of antennas provided various communications and data services between spacecraft and NASA centers, as well as tracked and ranged moving spacecraft. In its final years, it served as the primary voice and data link during the first 7½ minutes of Space Shuttle launches, and the final 13 minutes of shuttle landings at KSC. Though it occupied land at KSC, MILA was operated and managed by the Goddard Space Flight Center.
TDRS-4, known before launch as TDRS-D, is an American communications satellite, of first generation, which was operated by NASA as part of the Tracking and Data Relay Satellite System from 1989 until 2011. It was constructed by TRW, based on a custom satellite bus which was used for all seven of the first generation TDRS satellites.
TDRS-6, known before launch as TDRS-F, is an American communications satellite, of first generation, which is operated by NASA as part of the Tracking and Data Relay Satellite System. It was constructed by TRW, and is based on a custom satellite bus which was used for all seven first generation TDRS satellites.
The European Data Relay System (EDRS) system is a European constellation of GEO satellites that relay information and data between satellites, spacecraft, UAVs, and ground stations. The first components were launched in 2016 and 2019.
The NASA (Ground) Communications System (NASCOM) manages terrestrial communications between ground stations, mission control centers, and other elements of spacecraft ground segments. Established in 1964, NASCOM provides worldwide, near real-time, transmission of commands, telemetry, voice, and television signals. It is managed out of NASA's Goddard Space Flight Center in Greenbelt, Maryland.
A ground segment consists of all the ground-based elements of a space system used by operators and support personnel, as opposed to the space segment and user segment. The ground segment enables management of a spacecraft, and distribution of payload data and telemetry among interested parties on the ground. The primary elements of a ground segment are:
Tianlian also known as CTDRS, is a Chinese data relay communication satellite constellation. The constellation serves to relay data from ground stations to spacecraft and rockets, most significantly China's crewed spaceflight program. The system currently consists of seven satellites in two generations, with the first satellite being launched in 2008.
Differenced one-way doppler (DOWD) is a method of spacecraft navigation. The process uses two TDRSS communications relay satellites receiving the same telemetry broadcast from a satellite. The Doppler shifts experienced by both TDRS satellites can be processed using ground equipment to generate trajectory estimates without the need for onboard GPS solutions. The Flight Dynamics Facility at GSFC provides this trajectory processing for NASA missions, though commercial software can also be used.
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