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International Laser Ranging Service (ILRS)


Governing Board Chair: Toshimichi Otsubo (Japan)
Central Bureau Director: Michael Pearlman (USA)
Central Bureau Secretary: Carey Noll (USA)


The ILRS was organized as one of the IAG measurement services in 1998, with a charter to organize and coordinate world-wide Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) to support programs in geodesy, geophysics, and lunar and planetary science, and to provide the data products (Earth center of mass and scale) important to the maintenance and improvement of the International Terrestrial Reference Frame (ITRF). The basic observables in SLR/LLR are the precise two-way time-of-flight of an ultra- short laser pulse to a retroreflector array on a satellite or on the surface of the Moon, and the one-way time of flight to a space borne receiver (transponder). These observations enable the computation of precision ephemerides, calibration and performance validation to support active Earth sensing and space science missions (e.g. altimetry, gravity, relativity, etc.) and one-way ranging to support extraterrestrial missions with optical sensors.

The ILRS maintains a comprehensive website as its primary vehicle for the distribution of information for both the ILRS and the outside community at http://ilrs.gsfc.nasa.gov/.


Data Products

The ILRS SLR data are made available to the community and are also used by the ILRS Analysis Centers to generate fundamental data products, including: accurate satellite ephemerides, Earth orientation parameters, absolute coordinates and velocities of the ILRS tracking stations, time-varying geocenter coordinates, static and time-varying coefficients of Earth's gravity field, and fundamental physical constants. The ILRS generates a standard product of weekly station positions and daily Earth orientation parameters that are submitted to the IERS, and produces LAGEOS and ETALON multi-year combination solutions for maintenance of the International Terrestrial Reference Frame (ITRF). Lunar Laser Ranging (LLR) data are used to generate lunar ephemerides and librations, lunar orientation parameters, and other parameters to describe Earth-Moon dynamics. LLR has also become one of the strongest tools for testing Einstein's theory of general relativity in the solar system.

See: http://ilrs.gsfc.nasa.gov/products_formats_procedures/ilrs_products_desc.html



The ILRS organization includes the following permanent components:

  • Tracking Stations (38)
  • Operations Centers (2)
  • Global Data Centers (2)
  • Analysis Centers (9)
  • Associate Analysis Centers (14)
  • LLR Associate Analysis Centers (3)
  • Central Bureau
  • Governing Board
  • Working Groups

Details on these functions can be found at: http://ilrs.gsfc.nasa.gov/about_ilrs/index.html


Mission Support

Satellite Laser Ranging (SLR)


ILRS Network includes 38 SLR stations; several additional stations, now being established, plan to join. Approximately 50 targets are presently being tracked at LEO, MEO, GNSS, and synchronous altitudes. Large numbers of GLONASS satellites have recently been added to the roster and many more are expected from the GPS, Galileo, Compass and other planned GNSS complexes. The LAGEOS and ETALON satellites are the reference targets for the ITRF; but other satellites such as Starlette and Stella are being tested for future contribution to the process. 

The network stations provide their data on a routine basis to the CDDIS and the EDC where parallel data files are maintained for access by the users. Stations are expected to meet ILRS data accuracy, quantity, and timeliness standards. Data are regularly analyzed by at least one Analysis or mission-specific Associate Analysis Center. Many of the SLR stations are also now involved with one-way ranging to the Lunar Reconnaissance Orbiter (LRO) and with time transfer activities (e.g., T2L2).

Lunar Laser Ranging


Three laser ranging stations currently range to the five retroreflector arrays on the surface of the Moon. Several additional stations have lunar ranging capability and plan to join the activity. LLR data are collected, archived and distributed under the auspices of ILRS at its data centers, CDDIS and EDC, and made available to users. LLR data have been available on a continuous basis for over 40 years, providing a long continuous time series, albeit from a very limited number of stations.


Publications and Meetings

The ILRS holds its International Workshops on Laser Ranging every two to three years. Workshop sessions cover the applicable and supported science, operations, technology, and software. Seehttp://ilrs.gsfc.nasa.gov/reports/workshop/index.html.

The ILRS holds its General Assembly traditionally at the workshop. The Governing Board meets biannually. The Central Bureau meets monthly.

Many ILRS and related publications and reports can be accessed online through the ILRS website including:

  • ILRS Bi-annual Reports
  • ILRS Governing Board Meeting notes
  • ILRS Working Group Minutes and Reports
  • Science and Engineering References and Reports

See: http://ilrs.gsfc.nasa.gov/reports/index.html for links to these reports.

Content of this contribution provided by Erricos Pavlis.

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