I'm a MSC student in computer science. For my thesis I'm using SGP4 tool to propagate a LEO satellite.

If I have understood rightly, the SPG4 returns the two state vectors r and v in TEME format. (celestrak).

Here my problem: I need to obtain the Keplerian orbital parameter from those two vectors but I have some conversion trouble. I can't figure the difference between TEME and ECI. Are they the same? Can I convert from TEME with this method?



1 Answer 1


ECI doesn't have an actual reference time, it's just an arbitrary one that is useful. It works well for rockets and things with limited lifespans, but for satellites it is a bit trickier. As Celestrak states:

What is the reference frame of the resulting coordinates? This question is a bit more technical than most we have covered. To be precise, the reference frame of the Earth-centered inertial (ECI) coordinates produced by the SGP4/SDP4 orbital model is true equator, mean equinox (TEME) of epoch.

There is a whole article on how to properly use the coordinates. Using that article, and the question you linked, you should be able to make the conversion you require.


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