[Spice_discussion] spkezr question

[Aimee Mostella]

Hello,

I'm using spkezr to get the position of a spacecraft (target) in the  
J2000 reference frame with the observer as the Sun.  What coordinate  
system is this based upon?  Is it Heliocentric Aries Ecliptic HAEJ2000?

Ultimately, I need to get the lat and lon of the spacecraft based on  
the Heliocentric of Date (HCD) coordinate system so that I can  
convert to Heliocentric RTN (HGRTN).  I thought I could either get  
the position of the spacecraft in HAEJ2000 and convert to HCD from  
there or get the position in GEIJ2000 and convert from there.   
However, when I tried the GEIJ2000 route, my calculations were more  
off than they were when I did it from scratch.  I tried the algorithm  
in the SPK Required Reading but still didn't get a good answer.  Any  
suggestions?

Thanks

~~~~~~~~~~~~~~~~~~~~~~~
Aimee Mostella
Research Analyst
Southwest Research Institute
Space Science Division
(210) 522-6735

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