Re: Possible further elset developments
Phil Rogers (progers@mindspring.com)
Thu, 1 Apr 1999 15:23:09 -0500
Sven Grahn <svengrahn@mail.wineasy.se> wrote:
>At 10:39 AM 4/1/99 +0200, Björn Gimle wrote:
>>>See ftp://tie.jpl.nasa.gov/pub/dransom/current.data/flash.txt
>>>
>>The prospect of a new TLE format with a secret algorithm is not appealing.
>
>It beats me what the purpose of keeping the algorithm secret is. Then the
>elsets are useless! Is this an April Fool's Day joke?
>Sven
Dave Ransom apparently wrote:
>NEWS AND COMMENT by Dave Ransom
>
>mailto:rans7500@spacelink.nasa.gov
>
>[Reposted from the RPV Astronomy BBS @ (520) 282-5559]
>---snip---
>31 MAR 99 Reliable sources inform me that USSPACECOM would like to
> change the orbital model used for all TLEs and do NOT plan
> to release the code for their new "Special Perturbations"
> model. Since the "General Perturbations" model, SGP4/SDP4,
> is used in STSPLUS and most other satellite tracking programs,
> such a change would render that software all but useless
> except for historical purposes. I'll continue to track the
> situation and post Bulletins on my RPV BBS and FLASH.TXT on
> my Home Page as I learn more.
NORAD's Special Perturbations model is nothing new and is indeed the
model which has for years been used to generate all NORAD elsets.
As far as I know, NORAD has never used the General Perturbations
model in their data generation, but rather has distributed this
algorithm to all of their sensors to be used for their own orbital
calculations since it is more compact, faster and easier to use on the
small to medium scale mainframes commonly used for that purpose.
The primary difference between the two models is that while the
GP model is suited to generating elsets which remain valid only for a
few days, the SP model elsets can still be valid as long as two weeks or
more after generation, barring any external intervention with a given
sat's orbit. For this reason, NORAD's elsets are always to be preferred
over elsets of any other source because of their longevity of life.
Phil Rogers
progers@mindspring.com
********