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, and the International Space Station. This system was designed to replace a pre-existing worldwide network of ground stations that had supported all of NASA's manned flight missions and unmanned 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, 22,300 miles above the surface of the Earth.
The first seven TDRSS satellites were built by the TRW corporation. The three later versions have been manufactured by the Boeing corporation's Satellite Systems division. Ten satellites have been launched; however, one was destroyed in a launch failure (the Challenger disaster). TDRS-1 was decommissioned in mid-2010. Eight TDRSS satellites are still in service.[1] All of the TDRSS satellites have been managed by NASA's Goddard Space Flight Center.[2] The contract for TDRS versions L & K was awarded to Boeing on December 20, 2007.[3] On November 30, 2011, NASA announced the decision to order an additional third-generation TDRS satellite, TDRS M.[4]
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The first Tracking and Data Relay Satellite was launched in 1983 on the Space Shuttle Challenger's's first flight, STS-6. The Boeing-built Inertial Upper Stage that was to take the satellite from Challenger's orbit to its ultimate geosynchronous orbit suffered a failure that caused it not to deliver the TDRS to the correct orbit. As a result, it was necessary to command the satellite to use its onboard rocket thrusters to move it into its correct orbit. This expenditure of fuel reduced its capability to remain in an untilted geosynchronous orbit, and this TDRS, in orbit for a long time, has been re-assigned to the part-time mission of supporting communications to Antarctic scientific stations.
The second Tracking and Data Relay Satellite was destroyed along with Challenger shortly after launch during the STS-51-L mission in January 1986. The next five TRW-built TDRSS satellites were successfully launched on other Space Shuttles. Three follow-up Boeing-built satellites were launched by Atlas rockets in 2000 and 2002. A NASA Press Release[5] summarized the capabilities of the system as a whole:
"Working solo, TDRS-1 provided more communication coverage, in support of the September 1983 Shuttle mission, than the entire network of NASA tracking stations had provided in all previous Shuttle missions."
The first generation of TDRS are planned to be retired in 2015.[4]
The two TDRSS satellite ground terminals are located at White Sands Test Facility, which is in the Las Cruces area. All radioed commands and received telemetry that go to and from the Tracking and Data Relay Satellites go by way of these terminals at White Sands Test Facility. At first, just one large ground terminal system for the TDRSS was designed and built. However, some years later, due to increased user demand NASA ordered the design and construction of a second ground terminal system just over three miles away. Thus, there are now two functionally-identical and redundant satellite ground terminals there, which are known as the White Sands Complex. Due to a Zone of Exclusion, no user support over the Indian Ocean, a Ground Terminal was built in Guam to support TDRS.[1]
The Bilateration Ranging Transponder System (BRTS) provides tracking support for TDRS spacecraft. BRTS consists of four sites located at White Sands Missile Range (WSC), American Samoa (AMS), Ascension Island (ACN), and Alice Springs, Australia (ALS).[6]
The communications systems of the TDRSS satellites were designed to support multiple missions at the same time. Each satellite has S band, Ku band (1st Gen only), and Ka band (2nd gen only) electronic communication systems hardware that operate at different carrier frequencies and also support various data-rates.[7] The newer Boeing satellites are able to support more communications than the older TRW-built satellites.
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.
| Name | Launch date | Mission name | NSSDC ID No. | Notes |
|---|---|---|---|---|
| TDRS A | April 4, 1983 | STS-6 | 1983-026B[10] | also TDRS 1; first of the first generation of TRW TDRS; Decommissioned in October 2009[11] |
| TDRS B | January 28, 1986 | STS-51-L | TDRSS-B[12] | also TDRS 2; destroyed in the Challenger disaster |
| TDRS C | Sept. 29, 1988 | STS-26 | 1988-091B[13] | also TDRS 3 |
| TDRS D | March 13, 1989 | STS-29 | 1989-021B[14] | also TDRS 4 |
| TDRS E | August 2, 1991 | STS-43 | 1991-054B[15] | also TDRS 5 |
| TDRS F | January 13, 1993 | STS-54 | 1993-003B[16] | also TDRS 6 |
| TDRS G | July 13, 1995 | STS-70 | 1995-003B[17] | also TDRS 7; replacement for the lost TDRS B |
| TDRS H | June 30, 2000 | Atlas IIa | 2000-034A[18] | also TDRS 8; first of the second generation of Boeing TDRS |
| TDRS I | March 8, 2002 | Atlas IIa | 2002-011A[19] | also TDRS 9 |
| TDRS J | December 4, 2002 | Atlas IIa | 2002-055A[20] | also TDRS 10 |
| TDRS K | 2012 (Planned) | Atlas V | to be TDRS 11; first of the third generation of Boeing TDRS | |
| TDRS L | 2013 (Planned) | Atlas V | to be TDRS 12 | |
| TDRS M | Unknown |
TDRS-A was the first of TDRSS multiple satellite tracking system. The system is a concept utilizing communication satellite technology that improves and economizes the satellite tracking and telemetry operations. The base three geosynchronous satellites (one a standby) track and receive data from satellites for relay to a ground station. The two primary active satellites are separated in orbit by at least 130 degrees longitude.
One system is used for tracking satellites with apogees below 2000 km (the great majority of satellites), and the other for those with higher apogees. Use of operating frequencies near 2150 (plus or minus 150) MHz and near 14.3 (plus or minus 0.9) GHz were the initial plan.
TDRSS was originally intended to support satellites with apogees below 12,000 km. Spacecraft in the TDRSS System require only one communications system, since ground-based telemetry stations will be compatible with TDRSS equipment.
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