Precise orbits products

ILRS Analysis Centers provide weekly satellite orbit solutions for LAGEOS-1 and -2 and Etalon-1 and -2 to the CDDIS using pre-determined schedules. The orbits are computed using SLR data collected over the previous seven days; their reference frame is the Earth Centered-Earth Fixed (ECEF) realized by the latest SLR reference frame and the IERS Bulletin A EOP series (USNO). The ILRS combination centers retrieve these solutions to produce the ILRS-A and ILRS-B combined product, which is then in turn archived at the CDDIS. These combination solutions are considered the official ILRS orbit products.

The final combined ILRS orbit solutions, consists of weekly orbit files, generated on a weekly basis approximately 10 days after the end of the solution week. All orbit solution files utilize the Extended Standard Product-3 (SP3c) format.

The ILRS orbit products are archived in subdirectories by satellite and date; the date is the end of the 7-day interval spanned by the orbit. Each subdirectory contains the individual AC solutions, the two combined solutions and corresponding summary files.

The starting directory for these files is:

Append the following directory and file names to the starting directory:


as described in the table below.

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CodeAnalysis Center
bkgBundesamt für Kartographie und Geodäesie (BKG) Germany
dgfiDeutsches Geodätisches Forschungsinstitut (DGFI) Germany
esaESA/ESOC, Germany
grgsGroupe de Recherche en Géodésie Spatiale (GRGS) France
gfzHelmholtz Centre Potsdam German Research Centre for Geosciences (GFZ), Germany
ilrsaILRS primary combination solution
ilrsbILRS backup combination solution
afiItalian Space Agency, Centro de Geodasia Spaziale "G. Colombo" (ASI/CGS), Italy
jcetJoint Center for Earth System Technology/Goddard Space Flight Center (JCET/GSFC) Greenbelt, Maryland, USA
ngsfNERC Space Geodesy Facility (NSGF) formely RGO Satellite Laser Ranging Group, United Kingdom

More about ILRS Analysis Centers

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Satellite name
Code Meaning
SATNAMESatellite Name
ACNAME Analysis Center Name
YY2-digit year
MM2-digit month
DD 2-digit day
NN version number
Z Unix compressed file