I have an EARTH ORIENTATION PARAMETERS (EOP) DATA file taken from CelesTrak to convert data from ECI to ECEF. The same file used by STK for the Scenario to be clear.

However its predictions stop at April 2023. I want to extend those values for the next years in the same way STK does. How can I do that?

I've tried by interpolation, the linear interpolation is the one that suits best currently, but when I compare the satellite position e velocity computed by STK in ECEF with mine obtained converting STK's values in ECI to ECEF, the maximum absolute error is of about 20 m.

Thanks in advance!


1 Answer 1


Any predictions of the Earth Orientation Parameters that go beyond a few months to a year into the future are more or less worthless. What you can do, and I suspect what STK does (I don't use that tool), is to set dUT1, the coordinates of the pole, and the celestial pole offsets to zero. You'll still have precession and nutation.

The International Earth Rotation and Reference Systems Service (IERS) provides predictions of dUT1 and coordinates of the pole about a year into the future. For the celestial pole offsets, the predictions are just a few months into the future. But unless you're doing milliarcsecond astronomy, you can ignore those celestial pole offsets.

If you are a programmer, I would recommend using the Standards Of Fundamental Astronomy library. The SOFA is freely distributed and has the right kind of software license for almost any use. There are cookbooks that describe how to use the library for time, Earth attitude, and other items.

  • $\begingroup$ IERS Bulletin A's e.g. most recent example have prediction formulae and a table going out 12 months for the $x, y$ pole position and for $UT1-UTC$ along with estimated uncertainties. $\endgroup$ Commented Oct 13, 2022 at 22:32

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