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Read Me documentation for USNO Ultra-Rapid Products


  • Files available:

    • GPS-satellite orbit + clock files (IGS .sp3 format)

    • Earth-orientation files (IGS .erp format)

  • Each file provides 48 hours of solutions:

    • 24 hours of post-processed solutions

    • 24 hours of predictions

    • These files are also available via anonymous ftp at

  • File name indicates center date/time of 48-hr span

    • before date = post-processed

    • after date = predict

  • Frequency/latency: produced every six hours, available three hours after center epoch.

  • File names (by example):

    • usu15002_18.sp3: 48-hr orbit/clock file with center date GPS week 1500, day 2 (Tuesday), hour 18 (GPST)

      • general format: usuwwwwd_hh.sp3

    • Similarly, usu15002_18.erp


To learn more about these products, click here.

USNO Master Clock Time
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