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I'm developing a software to show the planets in the sky. I have loaded the following kernels:

\naif\kernels\Generic\LSK\naif0012.tls
\naif\kernels\Generic\PCK\pck00010.tpc
\naif\kernels\Generic\PCK\gm_de431.tpc
\naif\kernels\Generic\SPK\planets\de440s.bsp
\naif\kernels\INSIGHT\SPK\mar097s.bsp

But I get the error:

Insufficient ephemeris data has been loaded to compute the position of 699 (SATURN) relative to 0 (SOLAR SYSTEM BARYCENTER) at the ephemeris epoch 2023 NOV 06 19:16:53.612.

I have no idea about how to know which kernels to use if I want to show Jupiter and Saturn. Now, I can show all the inner planets.

How can I solve this error?

I have read a lot about SPICE kernels, but I don't understand anything.

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    $\begingroup$ This question may be a duplicate but also doesn't have an answer, just a comment about using the brief utility to check the time coverage of the kernels. $\endgroup$
    – Erin Anne
    Nov 6, 2023 at 20:16
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    $\begingroup$ Does it work with the gm_de440.tpc instead of the gm_de431 one ? Suspect this may due to the change of origin in DE440... $\endgroup$ Nov 7, 2023 at 5:00
  • $\begingroup$ @astrosnapper DE440 and DE431 use the same origin, which is the solar system barycenter. The problem is choosing Saturn versus the Saturn system barycenter; see my answer. $\endgroup$ Nov 7, 2023 at 13:20
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    $\begingroup$ FYI: The JPL DE's your're using are overkill for displaying the position on a screen. Most planetarium applications use VSOP87, which can be easily truncated to produce only the level of accuracy needed. It's also much, much smaller over a long time period, and still provides higher accuracy than most amateurs need. This repo has implementations in many languages: github.com/gmiller123456/vsop87-multilang $\endgroup$ Nov 7, 2023 at 13:42
  • $\begingroup$ @DavidHammen But the SSB differs slightly in DE440/441. From ssd.jpl.nasa.gov/horizons/news.html April 12, 2021 "Due to the addition of KBO mass in DE440/441, the SSB has shifted about 100 km". $\endgroup$
    – PM 2Ring
    Nov 8, 2023 at 6:08

1 Answer 1

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Insufficient ephemeris data has been loaded to compute the position of 699 (SATURN) relative to 0 (SOLAR SYSTEM BARYCENTER) at the ephemeris epoch 2023 NOV 06 19:16:53.612.

That's because you are asking for the position of Saturn (the planet) with respect to the solar system barycenter. You have provided two Development Ephemeris kernels, DE431 and DE440. (Aside: There's no reason to supply both.) The Development Ephemerides give the states of the barycenters of the planetary systems with respect to the SSB.

Because Saturn is so much more massive than all of its moons, you won't see much error asking for the position of the Saturn system barycenter (ID=6) as opposed to Saturn itself (ID=699). If you truly do want the position of Saturn itself you will need to provide an additional kernel that specifies the positions of Saturn and its moons relative to the Saturn system barycenter.

Per Horizons, the difference in position between the Saturn system barycenter and Saturn itself is about 300 meters. If you truly do want the position of Saturn rather than the Saturn system barycenter you will need to supply a kernel for the Saturn system as well as one of the Development Ephemerides. Horizons is currently using naif/generic/spk/satellites/sat441.bsp.

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  • $\begingroup$ Thanks a lot! Where did you learn all that? I've been reading about kernels a lot, but I have no idea about how to use it, and I don't understand them. I don't know if I have to create my own, because I don't know what's in them. Any suggestions about what to read. Thank you. $\endgroup$
    – VansFannel
    Nov 7, 2023 at 14:09
  • $\begingroup$ By the way, I don't know if gm_de431.tpc has the same content than de431.tpc which you have mentioned in your answer, but I'm using gm_de431.tpc. $\endgroup$
    – VansFannel
    Nov 7, 2023 at 16:07
  • $\begingroup$ @VansFannel Are you familiar with wgc.jpl.nasa.gov:8443/webgeocalc ? You may find it a helpful tool for exploration and experimentation with SPICE kernels. $\endgroup$
    – PM 2Ring
    Nov 8, 2023 at 6:15

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