In an application I have to analyse I found this trajectory description for the space probe cassini, unfortunately header and comments have been removed:

2004 6 01 00.0 16669287.46 -13098482.32 -10225933.05 1313468.24

The file format is .trj / .traj. Supposedly, there was a tool called SKYMAP which created these? I would like to know which tool created this data set. From the source code I gather that the table is in the format

year month day hour ignore x y z

The column ignore is ..ignored. I tried to recreate the output with JPL's horizons system but it does not quite fit.

edit: When we develop the application further I want it to be ready for future space missions. I might replace the trajectory description completely. I know asking for opinions is frowned upon, but what would you choose: spice toolkit or horizons toolkit? The spice toolkit seems more extensive and well-kept.

  • $\begingroup$ You may have more luck with naif.jpl.nasa.gov/pub/naif/CASSINI/kernels/spk/aareadme.txt and the directory that contains it. $\endgroup$
    – user7073
    Dec 11, 2017 at 14:39
  • $\begingroup$ I have -1.309744668548817E+07, -1.022795628362075E+07, 1.313137771804283E+06 in an old Horizons download. Your numbers are different by about 2300 km. That's bigger than the light-time difference (~ 300km), but smaller than the difference between barycentric and sun-centered (~65,000km), so dunno. $\endgroup$
    – uhoh
    Dec 11, 2017 at 17:37

1 Answer 1


It seems the traj format was a custom format created from a spice kernel just for the application. In the end, we managed to load the original spice kernels using a meta-kernel file and the spice tools making the traj file format obsolete.


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