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    Discussion Improved (Tesseral) Gravity Model

    I conducted more test with different orders/degrees, inclinations, altitudes. Didn't find problems. Simulates definitely much closer to GMAT than with default Orbiters' model based on JCoeffs. For example, a polar orbit with EGM96: And the default model: An Impressive difference.
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    Discussion Improved (Tesseral) Gravity Model

    I wasn't able to find file with spherical harmonic coefficients in correct format for Earth, so I made one from egm96_to360.ascii (EGM96 360x360 model) that is available on the Internet. The file is in the attachment. Did a comparison with GMAT. Fits perfectly:
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    Discussion Improved (Tesseral) Gravity Model

    No, I use SPICE with x64. BTW, it may be a reason of the freezes. Needs investigation too.
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    Discussion Improved (Tesseral) Gravity Model

    It was "tacc 1000" with 10 Hz in FlightData settings. Without graphics engines it gives relatively small steps < 1s and I didn't expect any problems. Looks like the step increased due to unknown reasons and that affected precision (just huge step itself or with Orbit Stabilization). I test both...
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    Discussion Improved (Tesseral) Gravity Model

    It should be recording FlightData.log every ~100 simulated seconds and there were two gaps: ... 121789.83 170.3096 121890.15 170.1104 122111.46 169.8282 122211.78 169.7923 ... 128134.28 169.9225 128234.44 169.5184 128771.03 168.9129 128879.17 169.1444 ... which seemingly...
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    Discussion Improved (Tesseral) Gravity Model

    Excellent job! I did some test and compared the new improved gravity model in OpenOrbiter with GMAT's models (even made a script for converting *.tab files to GMAT's *.cof files). Orbiter and GMAT are very close now. An orbit around Mars for example: But once, only once, I got a strange...
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    Better Ephemerides, Rotation Models, and a Solution to X64 Builds

    Look here: https://orbiter-forum.com/threads/improved-tesseral-gravity-model.40266/post-602936 Kernels\orbiter.mrg is the config file for spkmerge tool (from SPICE toolkit) that creates *.bsp form other *.bsp. Original kernels are here: https://naif.jpl.nasa.gov/pub/naif/generic_kernels/spk/
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    Better Ephemerides, Rotation Models, and a Solution to X64 Builds

    Orbiter now has an API for implementing any ephemerides. It's just a matter of packaging and perhaps revising some existing plugins, such as the SPICE module. However, an API for utilizing better rotation models still needs to be implemented in the OpenOrbiter core, preferably as an extension of...
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    TransX TranX lowering orbit instead of raising it

    You need to use the minor view for the eject function and the maneuver has to minimize R.Inc and DeltaV: https://orbitermars.co.uk/txmanfneject2.htm It may or may not be the prograde burn relative to Earth. Depends on your parking orbit and your current position on the orbit.
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    TransX TranX lowering orbit instead of raising it

    Prograde relative to what? Earth?
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    Discussion Improved (Tesseral) Gravity Model

    And one more very important thing, the MJD epoch in Orbiter is TDBModJulian+29999.5 epoch in GMAT. Not UTC/TT/A1/etc.
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    Discussion Improved (Tesseral) Gravity Model

    I would also recommend SPICE module: https://www.orbiter-forum.com/threads/spice-module.1108/ I've uploaded the latest ready-to-use build with all configs and SPICE kernels here: https://mega.nz/file/Vmxh2YyQ#IvMlr1d1NvgnE8im4Bk4oFvdlgUlEaZ9Z8N7HJidutg For x64 version of Orbiter you need to...
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    Discussion Improved (Tesseral) Gravity Model

    I don't think so. The difference in the moon's orientation for MJD 52006 between GMAT's (MOON_PA) and Orbiter ~0.001 rad. Have you compared results with GMAT\data\gravity\luna\grgm900c.cof model?
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    CAPSTONE mission

    BTW, they have removed the data after Nov 14 from Horizons. Now it's only:
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    Question Artemis 1 trajectory

    Nov 14 trajectory:
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    Longitude of ascending node of the Earth

    Yes, for example if you try to get elliptical osculating elements for Earth for an arbitrary date from Horizons System ( https://ssd.jpl.nasa.gov/horizons/app.html#/ ) using J2000 reference frame you get almost random LAN between 0 and 360 deg. :)
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    CAPSTONE mission

    Yes, I can confirm, there are course corrections before Nov 14-15, but after that it's ballistics. I was even able to find some parameters for solar radiation pressure model to get almost the same POS/VEL after propagating Nov 15 - Dec 14: HORIZONS (Moon body center, Ecliptic of J2000.0 )...
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    CAPSTONE mission

    Yes, I used GMAT. And yes, according to GMAT as well as Orbiter CAPSTONE with this POS/VEL from HORIZONS escapes Moon just soon after 14 Dec. Moreover, it looks like it's already way off NRHO, so I think there should be corrections before this date (and after 14 Nov) which were not included in...
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    CAPSTONE mission

    HORIZONS says "Data through Oct 23, predictions thereafter" I think everything after Oct 23 is just calculated ballistics without corrections.
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    CAPSTONE mission

    Looks fine. For example, if you try to propagate backward from 14 Dec 2022 there is the trajectory:
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