[Spice_discussion] SPKs for HST?

[Charles H. Acton]

       A question about production of SPICE SPK files for HST

Occasionally over the last year or two NAIF has been asked to make an 
SPK file (trajectory file) for the Hubble Space Telescope, to support 
reduction of solar system observations taken by HST.  On these 
occasions NAIF has gotten so-called "two line elements" for HST from 
the Space Track website (space-track.org) and used our MKSPK utility 
to make an SPK from those elements.

This process is available to anyone, after first registering with 
Space Track in order to be able to get 2-line elements.  (It could be 
used for other earth orbiting satellites as well, as long as 2-line 
elements sets are provided by Space Track.)

That said, we must also note that there have been some times when the 
2-line elements returned from Space Track are really not sufficient 
to produce a good orbit solution at all time within the bounding 
element sets... still a mystery to us.

The Space Telescope Science Institute also makes (or gets from GSFC) 
orbit files for HST, apparently both "predict" for planning and 
"definitive" for data analysis. I think--but am not sure--that both 
predictive and definitive orbit data are provided in a single format: 
*.orb.  (Used to be *.orx?)

A question for SPICE users: would it be useful if some entity such as 
StSciI or NAIF were to set up a regular HST SPK production process, 
making those SPK files available through whatever distribution 
channel is available (e.g. the archive website at STSciI, 
http://archive.stsci.edu/, or the NAIF server at JPL?  If you answer 
"yes," what caveats (requirements) would go along with your answer?

The alternatives are:

   - NAIF hand make an SPK for HST on the rare occasion when such is needed;

and/or

   - You the customer can get the 2-line elements (or perhaps an *.ORB 
file?) and use NAIF's MKSPK file to make an SPK on those occasions 
when you need such.

Are there earth orbiters other than HST for which SPKs would be useful?

Of course there is no promise that anyone can and will take some 
positive action on this.

Thanks in advance for your thoughts on this. You can answer to the 
entire distribution list or just to Chuck Acton, as you like.


Chuck Acton
NAIF Manager/JPL