[Spice_discussion] Magnetic coordinates

William Thompson William.T.Thompson.1 at gsfc.nasa.gov
Thu Mar 18 12:10:44 PST 2004


I've recently downloaded and installed the Icy/C-SPICE package, and have been 
able to use it to read a draft trajectory file for the upcoming STEREO mission. 
  I've been able to figure out most of what I need to know, but I have a few 
questions which may have already been addressed by other people or projects. 
Some of these may require additional data files which I don't yet have.  Please 
excuse me if these questions are off-topic for this list.

My main question has to do with magnetic coordinates.  How do I derive positions 
in coordinate systems which have Earth's magnetic dipole as one of the axes, 
such as GSM, SM, or MAG?  My suspicion is that I would have to have an 
additional data file, such as a PCK or FRM file, giving the orientation of 
Earth's magnetic axis as a function of time, including secular drifts.  Does 
such a thing exist?

My other question should be much simpler.  I'm able to derive ecliptic 
coordinates in the J2000 reference frame using SPKEZR.  I need to convert these 
to the mean ecliptic of date.  I've found some equations which should allow me 
to do this, but I wondered if there was already a simple way to do this already 
built-in to SPICE?

Thank you,

William Thompson
NASA Goddard Space Flight Center
Code 682.3
Greenbelt, MD  20771

William.T.Thompson.1 at gsfc.nasa.gov

(Please note changed email address.)

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