A general question: is the Orekit TEME frame “of epoch” or “of date?”
Thanks!
Good question!
There are no official consensus here, it is a well known ambiguity.
In the Orekit implementation, it is “of date” as shown by TEMEProvider.java line 114.
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Thanks for your reply Luc!
The link you provided references the equation of the equinoxes, which is the difference between mean and apparent sidereal time (and perhaps mean and true equinox, or TEME vs TETE) at a specific time and date. The SGP4 issue of “of epoch” vs “of date” is the difference between the mean equinox of epoch and the mean equinox of date, or the difference between the position of the mean equinox at the time (or epoch) of the TLE that produced the ephemeris, and the time (or date) of each ephemeris point. I don’t dwell on the subject of reference frames too often so I easily forget the details, but I don’t think the reference you provided indicates that Orekit SGP4 ephemeris is “of date.” I have compared Orekit SGP4 ephemeris with ephemeris produced by the official Astro Standards and they agree out to the seventh decimal place in km–Astro Standards SGP4 claims to be “of epoch.” Is there a method in Orekit that will transform TEME from one arbitrary time to another?
Thanks
Denis
I am not sure. May be you could try to use Frame.getFrozenFrame() to freeze the TEME frame at epoch.