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Retroreflector Standards for GNSS Satellites

ILRS Technology and Engineering Activities

The service collects, merges, analyzes, archives and distributes Satellite Laser Ranging (SLR) and Lunar Laser Ranging (LLR) observation data sets to satisfy the objectives of scientific, engineering, and operational applications and programs. The basic observables are the precise two-way time-of-flight of an ultrashort laser pulse to a retroreflector array on a satellite or the Moon and the one-way time of flight to a space borne receiver (transponder). These data sets are made available to the community and are also used by the ILRS to generate fundamental data products, including: accurate satellite ephemerides, Earth orientation parameters, three-dimensional coordinates and velocities of the ILRS tracking stations, time-varying geocenter coordinates, static and time-varying coefficients of the Earth's gravity field, fundamental physical constants, lunar ephemerides and librations, and lunar orientation parameters.

Recent News

ILRS Governing Board Approves Resumption of Tracking for the Westpac Satellite - The ILRS Governing Board has approved resuming tracking of the WESTPAC mission, originally launched on July 10, 1998, and tracked by the ILRS from 1998 to 2002. The GB believes there is scientific justification for readmitting WESTPAC to the ILRS target list because routine SLR measurements could complement the data from the existing geodetic targets, particularly for gravity field recovery, and could also provide atmospheric and range error information.

The decommissioned geodetic satellite WESTPAC will be returned to the ILRS target list with a low priority, not resulting in a significant burden to station scheduling or impact on other priority targets. In tests led by the ILRS Network and Engineering Standing Committeee (NESC), ILRS stations have demonstrated that with good predictions Westpac can be tracked routinely during the day and night, without a significant impact on the station tracking schedules or at the expense of other ILRS targets.

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The ILRS Monthly Report Cards and Monthly Station Performance Assessment Maps have been updated - The ILRS Monthly Report Cards and Monthly Station Performance Assessment Maps have been updated to include LARES-2 in the geodetic satellite group (LAGEOS-1, LAGEOS-2, LARES). This change was made starting with the January 2025 release.

The ILRS Monthly Report Cards can be viewed at the following links:

Monthly Report Cards:
https://ilrs.gsfc.nasa.gov/network/system_performance/global_report_cards/monthly/index.html
Monthly Station Performance Assessment Maps:
https://ilrs.gsfc.nasa.gov/network/system_performance/monthly_station_performance_maps/index.html

This change was made in light of the plans of the ILRS Analysis Standing Committee (ASC) to include the contribution of LARES-2 in the development of the operational products of the ILRS (both the daily and the weekly solutions for station coordinates and Earth Orientation Parameters). Tests are currently underway, and the ASC will announce after the ASC meeting during the EGU General Assembly 2025, in Vienna, Austria (27 April – 2 May 2025) when this operational change will be made.