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Given a Keplerian Orbit description such as that in here:

[
  {
    "CCSDS_OMM_VERS": "2.0",
    "COMMENT": "GENERATED VIA SPACE-TRACK.ORG API",
    "CREATION_DATE": "2022-12-22T18:47:50",
    "ORIGINATOR": "18 SPCS",
    "OBJECT_NAME": "TBA - TO BE ASSIGNED",
    "OBJECT_ID": "",
    "CENTER_NAME": "EARTH",
    "REF_FRAME": "TEME",
    "TIME_SYSTEM": "UTC",
    "MEAN_ELEMENT_THEORY": "SGP4",
    "EPOCH": "2022-12-22T09:47:18.097440",
    "MEAN_MOTION": "12.95271318",
    "ECCENTRICITY": "0.00298554",
    "INCLINATION": "90.2548",
    "RA_OF_ASC_NODE": "337.7299",
    "ARG_OF_PERICENTER": "225.6432",
    "MEAN_ANOMALY": "134.2241",
    "EPHEMERIS_TYPE": "0",
    "CLASSIFICATION_TYPE": "U",
    "NORAD_CAT_ID": "270288",
    "ELEMENT_SET_NO": "999",
    "REV_AT_EPOCH": "12946",
    "BSTAR": "0.00171121940000",
    "MEAN_MOTION_DOT": "0.00000489",
    "MEAN_MOTION_DDOT": "0.0000000000000",
    "SEMIMAJOR_AXIS": "7658.811",
    "PERIOD": "111.174",
    "APOAPSIS": "1303.541",
    "PERIAPSIS": "1257.810",
    "OBJECT_TYPE": "UNKNOWN",
    "RCS_SIZE": null,
    "COUNTRY_CODE": null,
    "LAUNCH_DATE": null,
    "SITE": null,
    "DECAY_DATE": null,
    "FILE": "3719197",
    "GP_ID": "221188557",
    "TLE_LINE0": "0 TBA - TO BE ASSIGNED",
    "TLE_LINE1": "1 T0288U          22356.40784835  .00000489  00000-0  17112-2 0  9990",
    "TLE_LINE2": "2 T0288  90.2548 337.7299 0029855 225.6432 134.2241 12.95271318129469"
  }
]

How would I calculate the parameters needed to use the teme_eci function in David Vallado's AstroLib?

The signature for the function is:

    public void teme_eci
    (
        ref double[] rteme,
        ref double[] vteme,
        EOPSPWLib.iau80Class iau80arr,
        Enum direct,
        double ttt,
        double ddpsi,
        double ddeps,
        EOpt opt,
        ref double[] rgcrf, 
        ref double[] vgcrf
    )

Now I think rteme and vteme contain the position and velocity of the object at an arbitrary number of points around the orbit. Which I would assume can be calculated from the keplerian elements. However, I'm not sure what the position would be relative to (as it's just a single number), perhaps the centre of orbit? The same goes for the velocity, perhaps it's prograde velocity?

As for the rest, I have absolutely no idea what the parameters are so I've got even less idea how to calculate them.

ScottishTapWater
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  • rteme and vteme are 3 element arrays containing the x, y, z, position/velocity. You don't need to manipulate them directly, a call to sgp4() computes them. – Greg Miller Jan 08 '23 at 02:54
  • The information needed to describe the orbit of that long-since decayed launch vehicle is not present in that JSON record. It provides inclination, perigee, and apogee. At a minimum, seven parameters are needed. – David Hammen Jan 08 '23 at 05:21
  • @DavidHammen - Sorry, it had been a long, frustrating night by that point, I accidentally put the satcat entry rather than the elsat entry into my question, I've updated it – ScottishTapWater Jan 08 '23 at 15:02
  • @GregMiller - is that xyz, at any point, relative to the orbital centre? What do you mean I don't need to manipulate them directly? I need to provide them as function inputs? Although it is good to know they're 3 element arrays rather than arbitrarily sized ones – ScottishTapWater Jan 08 '23 at 18:01
  • Per the names of the variables, the input is in the TEME frame, and the output is in the GCRF. I would recommend looking at some of the examples on the website you linked. Also check out the "Computers and Satellites" link from the main page which has a lot of related info. – Greg Miller Jan 08 '23 at 18:12
  • @GregMiller - I don't believe that is the case, per the comment above the function "this function transforms a vector from the true equator mean equinox system, (teme) to the mean equator mean equinox (j2000) system" althout admittedly, J2000 and GCRF are very close. I also think you miss the point of my question, I'm not sure exactly what these variables need to be, so I can't even begin to work out what their values are from the keplerian components. I know they need to be in the TEME frame, but that doesn't tell me what velocities and what points etc – ScottishTapWater Jan 08 '23 at 18:16
  • I will take a look at some of the examples though in-case they can help inform me any further though, I hadn't noticed the examples section – ScottishTapWater Jan 08 '23 at 18:17
  • @GregMiller - I'd totally missed the columns section on the site, that's actually been a huge help so far! Thank you for pointing me back in that direction – ScottishTapWater Jan 10 '23 at 12:21

0 Answers0