# How to use “HORIZONS” tool by NASA to get orientation of comet 67P/Churyumov-Gerasimenko axis?

I found this powerful online tool from NASA: http://ssd.jpl.nasa.gov/horizons.cgi#top

It allows getting orbital data for the comet, but what I actually need is the orientation of the axis of the comet w.r.t to Sun, to build a 3d model which shows shadows changes during day.

Is it possible to retrieve such information using this tool? Or do I need another source like SPICE or others?

• – Jerard Puckett Nov 25 '14 at 13:30
• It's certainly not possible with HORIZONS, and I strongly doubt that there is a SPICE kernel that describes the orientation of 67P. Comets near the Sun (e.g., 67P) do not have a predictable orientation, at least not for long. All it takes is one good outgassing to make the rotational behavior change. – David Hammen Nov 25 '14 at 23:56
• I found axis orientation for "comet ellipsoid approximation", (RA=220, DEC=-70) and Prime Meridian rotation speed (679 degrees/day) (2012 data from ROS_CGS_RSOC_V03.TPC) But I don't know how to draw the prime meridian on the comet 3d model. I was also suggested to look at this file for orbital parameters: ORHW_______________00122.BSP in naif.jpl.nasa.gov/pub/naif/ROSETTA/kernels/spk But I don't know how to put all these data together... – jumpjack Nov 26 '14 at 9:39
• I also estimate that the only one knowing the current comet rotation axes is -- Rosetta. Its orbit propagator uses them (and more) to calculate how to reach a target landmark on the comet. – TheBlastOne Nov 27 '14 at 17:07
• There certainly is a SPICE kernel that describes the orientation of 67P, as would be expected with an active spacecraft orbiting it. It is updated every three or four days. – Mark Adler Dec 25 '15 at 23:59

Yes, SPICE is your best bet. The learning curve is steep but worth it.

You can start at the SPICE Required Reading.

and look at the PCK, FK and SPK required reading files. That will lead you to the other required reading files.

You also will need this Frames Kernel (FK)

Caveats:

That is not much guidance, and assumes you are a self-starter, but this is not the place for a tutorial, which will only lead you back to the NAIF/SPICE web site anyway.

That is the C version of that toolkit; versions also exist for FORTRAN, IDL, Matlab (and Octave), Java and Python.

I'm busy but I could gin up a quick example for you if you describe your environment in more detail (what does the display look like and/or emulate; what does the camera look like, where are you getting your shape model from).

As Brian Carcich noted, you will need to learn and use SPICE. There is a bit of a learning curve, but it is well worth it. You can find the latest kernel here. The latest CATT_*.BC file in that directory has the detailed orientation and rotation information for the comet. It looks like a new one is uploaded every three or four days. Look at the readme there for some information on how to use it.