DUT1 is defined by Wikipedia as follows:

The time correction DUT1 (sometimes also written DUT) is the difference between Universal Time (UT1), which is defined by Earth's rotation, and Coordinated Universal Time (UTC), which is defined by a network of precision atomic clocks.

Its value is relevant when performing conversions between the Earth-fixed frames and inertial frames at epochs identified by a UTC time stamp.

The plot provided by Wikipedia for the evolution of DUT1 is:

DUT1 Graph rom wikipedia

Meanwhile, I've tried to produce a reduced version of this graph with STK, only to find this:

enter image description here

It seems like STK does not update the value of DUT1 outside of the 2012 to 2016 interval, even though the scenario spanned from 2000 until 2019. Why does this happen? How can I be sure that DUT1 is being properly taken into account for frame transformations?

EDIT: When opening STK, going for "Utilities" and then "Data Update Utility" allows the user to download new Earth Orientation Parameters, along with other new data. This is likely the reason why the graph was constant after 2017. The updated picture is shown below.

After updating STK Data

Because this time the data is constant before 2013 instead of 2011, I'm guessing that STK loads valid parameters for this curve only for a period of around 5 or 6 years. Not sure about this, but would be nice if there was a fix for this.


You will see this STK behavior with both UT1-UTC and with polar motion parameters.

In STK, the default Earth Orientation Parameters file EOP-v1.1.txt only goes back 5 years. I'm guessing this is for quick loading. It also goes into the future with predictions by for about 1 year

HOWEVER, STK also has a much larger EOP file that goes all the way back to 1962. It is named EOP-All_v1.1.txt and resides in the same folder.

If you run the Data Update utility, both files are updated with the latest parameters and can be found in this default location: C:\ProgramData\AGI\STK 11 (x64)\DynamicEarthData

To get STK to use the ALL file, go into the properties of your scenario. Under Basic->Earth Data you can change the file that the scenario uses.

  • 2
    $\begingroup$ Yes, this solves the problem =) I was however amazed to see that, as of today, the small EOP file has 230kb, while the full one has 2140 kb. I'm not sure if this size difference is relevant for today's computers. $\endgroup$
    – Mefitico
    Sep 12 '19 at 16:22

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