Problems with NORAD/Celestrak TLEs

[Nigel Atkinson]

The seems to be a problem with the TLEs currently being issued by NORAD, which are published on the space-track or celestrak web sites. The validity time for many satellites is 6 days in the future, which causes problems for AAPP.

We recommend that you use EUMETSAT-supplied TLEs instead, as they don’t suffer from this problem. These are available at http://oiswww.eumetsat.org/metopTLEs/html/index.htm, for NOAA and NPP as well as Metop satellites. The easiest way to retrieve them is to use the AAPP “get_tle” script. In your ATOVS_ENV7 file, set


PAR_NAVIGATION_TLE_URL_DOWNLOAD='http://oiswww.eumetsat.org/metopTLEs/html/data_out/latest_n15_tle.txt'
PAR_NAVIGATION_TLE_URL_DOWNLOAD+=' http://oiswww.eumetsat.org/metopTLEs/html/data_out/latest_n18_tle.txt'
PAR_NAVIGATION_TLE_URL_DOWNLOAD+=' http://oiswww.eumetsat.org/metopTLEs/html/data_out/latest_n19_tle.txt'
PAR_NAVIGATION_TLE_URL_DOWNLOAD+=' http://oiswww.eumetsat.org/metopTLEs/html/data_out/latest_m02_tle.txt'
PAR_NAVIGATION_TLE_URL_DOWNLOAD+=' http://oiswww.eumetsat.org/metopTLEs/html/data_out/latest_m01_tle.txt'
PAR_NAVIGATION_TLE_URL_DOWNLOAD+=' http://oiswww.eumetsat.org/metopTLEs/html/data_out/latest_npp_tle.txt'


I hope that space-track will fix the problem soon.

If necessary, you can change parameter djmax in satpostle.F: an increase from 6.1 to 7.1 should allow the NORAD bulletins to be used, though the navigation accuracy would probably be degraded compared with using the EUMETSAT TLEs. You would need to re-compile using “make bin”.

Regards,

Nigel

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