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Last week someone asked about how old is old.  Today we had to compare
some 26 day old keps with 3 day old keps for one of our LEO birds in an
800 km circular orbit.  THis was a HIGH elevation pass above 60 degreees
where the angle rates very rapidly change during the peak.  Here are the
differences in AZ/EL noted:

    ELEVATION   Error in AZ   error in EL
    10 deg          1             1
    30 deg          3             1
    45 deg          6             5
    60 deg         19             0
    45 deg          5             6
    30 deg          3             1
    10 deg          1             1

SO you see that the differences are insignificant for amateur antennas.
Even the 20 degrees AZIMUTH error is insignificant, because 20 degrees of
AZIMUTH when looking up at 60 degrees is really less than 10 degrees of
actual difference...  MOST of the time duration of any pass is well under
30 degrees anyway...

The overall difference in access times was only a few seconds.


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