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I have a serious problem with some satellite state vector I use. I got the cartesian coordinates of ISS (X,Y,Z) but do not know in which frame unfortunately. So I tried to plot them in 3D to check if its ECEF or ECI and got this 3D view... it seems something is wrong as I clearly have an inclined orbit (which seems good) but that seems to rotate around the inclination axis?

Could not find why and how to correct those state vectors I have... or if a different rotation frame than ECI/ECEF is used for those state vectors?

note: 'm using the following link spotthestation.nasa.gov/trajectory_data.cfm and use the txt file to get X,Y,Z. When I plot the coordinates in 3D I get what it seems to be a rotating frame?

3D View 1 of state vectors

3D View 2 of state vectors

3D View 3 of state vectors

3D View 4 of state vectors (full dataset)

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    $\begingroup$ I'd expect they're in ECI (J2K specifically) based on experience with what ISS publishes, but can you link to where you got the data from? The plots aren't super helpful. $\endgroup$
    – Erin Anne
    Commented Oct 14, 2022 at 6:57
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    $\begingroup$ I'm using the following link : spotthestation.nasa.gov/trajectory_data.cfm and use the txt file to get X,Y,Z. When I plot the coordinates in 3D I get what it seems to be a rotating frame ? $\endgroup$
    – StateVect21
    Commented Oct 14, 2022 at 9:46
  • $\begingroup$ I would not expect it to rotate... $\endgroup$
    – StateVect21
    Commented Oct 14, 2022 at 10:03
  • $\begingroup$ That link says " ISS state vectors in the Mean of J2000 (J2K) reference frame". $\endgroup$
    – Greg Miller
    Commented Oct 14, 2022 at 12:44
  • $\begingroup$ Indeed, so I assume I see J2 perturbation effect on the orbital state vector along time ? $\endgroup$
    – StateVect21
    Commented Oct 14, 2022 at 13:10

1 Answer 1

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Top line answer: there is no problem with your plots or the state vectors

More Detail:

Because of the fact that earth is an oblate spheroid and not a perfect sphere, all inclined orbits exhibit some degree of precession, in which the orbital plane will rotate around earth's axis over some degree of time.

The ISS orbit undergoes a full plane precession cycle in approximately two months.

Examining the file you pointed to reveals that the data provided covers approximately two weeks worth of data, which would correspond to roughly 90 degrees of precession, which looks about right for your plots.

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