[Spice_discussion] Re: SPKs for HST?

Mark Showalter mshowalter at seti.org
Sat Dec 30 09:21:30 PST 2006


I agree with Dick.  I would like "official" SPKs for Hubble on those  
occasions when it is observing Solar System targets where precise  
geometry is needed.  This would include stellar occultations and  
maybe a few others events---for example, I could never resolve some  
pointing and timing issues with Metis and Adrastea at Jupiter; I  
suspect that HST's parallax may have played a role.

These issues could probably be handled on a "by request" basis.  As  
Dick notes, the number of such cases is rather small.

So I am endorsing your alternative #1.


On Dec 29, 2006, at 5:22 PM, Richard G. French wrote:

> "Charles H. Acton" <Charles.H.Acton at jpl.nasa.gov> writes:
>> 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?
> To me, the most important things about the HST SPK file are:
> 1) that it be accurate at the 100-meter level, or at least that its
> accuracy be clearly known
> 2) that it have a clear pedigree, so that others who want to  
> duplicate or
> test some published results will have an easy and unique way to  
> identify
> some property of the SPK file itself.
> 3) that the file have the NAIF or STSCI imprimatur of official  
> approval
> 4) that the file be directly usable with the SPICE toolkit, which  
> is the
> gold standard for planetary science spacecraft trajectory manipulation
> These makes me prefer that there be an end-product SPK file publicly
> available, since otherwise one is left in the uncertain situation of
> knowing if someone else's 2-line elements file conversion-to-SPK  
> routine
> had an error in a reference frame, epoch, ET-UTC correction, etc.
> There are not that many HST observations that I can think of where  
> knowing
> the parallax of the HST orbit and/or its orbital velocity are  
> important.
> Stellar occultations by planetary rings and atmospheres certainly fall
> into this category. Collectively, we could probably come up with  
> the full
> set of past HST observations for which SPK files would be desirable.
> Dick French

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