Comment 2 for bug 951045

Hi Matthew,

thanks a lot for the quick answer.
I've updated the satellites and the problem remains. The file is attached.

Looking to your help files and and to the whitepapers I understand, that
the regulary update of the TLE - data corrects the one time positions.
When I briefly read the descriptions of the mathematical theory behind
the comuptation (e.g.
http://www.celestrak.com/publications/AIAA/2006-6753/AIAA-2006-6753.pdf)
and the limits in Appendix B, the programm does it's best but the
accuracy can't be better....

------
1. The maximum accuracy for a TLE is limited by the number of decimal
places in each field (Vallado,
2004:116). In general, TLE data is accurate to about a kilometer or so
at epoch and*it quickly degrades* (Hartman,
1993). We note that the SGP4 theory is capable of much better accuracy
through additional modeling and sufficient
observational data. Cefola and McClain (1987) noted that certain
low-inclination geosynchronous orbits exhibited
*large discrepancies from numerical simulations due to
oversimplifications in the node rate calculations*. Cefola and
Fonte (1996) showed that the addition of additional terms to the theory
could improve the overall accuracy by
almost an order of magnitude. Cappellucci (2005) showed that using
numerically generated state vectors and
performing an SGP4 orbit determination on the resulting ephemerides
produced errors representative of a numerical
technique. This is not unexpected as additional (continuous)
observations provide the needed observability over a
simple “3-obs per pass” approach (Vallado and Alfano, 1999). However,
the results diverge very rapidly once
outside the fit span of the orbit determination. We do not address orbit
determination here.
---------

It would be very nice, if you could verify, that the code works as
designed :-)

Best wishes from Burscheid, Germany.
Detlev

Am 09.03.2012 20:57, schrieb Matthew Gates:
> Lots of geostationary satellites have some small wobble in their orbit,
> although this is usually only a fraction of a degree. You might have
> out-of-date orbital elements for this object. You can check like this:
>
> Please open the satellite config dialog (alt-Z), and click "update now",
> and check there is no error message. After this, please check if you
> still have the problem. If you so, I would like you to attach this file:
>
> C:\Users\Detlev\AppData\Roaming\Stellarium\modules\Satellites\satellites.json
>
> I can cross check it against mine and see if I can re-create the problem
> with it.
>
> M
>