Re: Which is correct?

From: Edward S Light (light@argoscomp.com)
Date: Wed Mar 22 2006 - 07:35:13 EST

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    Hi Greg,
    
    You recently posted to SeeSat ...
    > 
    > Ive had a look at several prediction programs to see if I could find which
    > was correct . I attach a specific example and would appreciate if you could
    > try your favourite prediction program to see if there is any agreement.
    > Whilst the difference in the three programs tried is not terrible it is
    > more than my 2 degree field of view will allow.
    > 
    > Time in all cases is South African Standard Time which is 2.0 hours fast on
    > UT. Angles in degrees.
    > 
    < ... stuff deleted ... >
    > 
    > Ive always found GUIDE to be pretty good and I also have confidence in Mikes
    > program - my one is normally okay but none of them agree.
    > 
    > Almost forgot - my coordinates needed !!
    > 
    > Longitude  +18.51284 (East)    Latitude  -33.94058 ( south )  Alt=10
    > metres
    > 
    < ... stuff deleted ... >
    > 
    > Element set used:
    > --------------------
    > Unknown 041206
    > 1 90027U 04841A   06071.55035598 0.00001113  00000-0  11045+1 0    09
    > 2 90027  62.3773 158.6750 6940454 268.4454  91.5512  2.00728666    05
    > 
    < ... stuff deleted ... >
    
    Using Rob Matson's Skymap program, which uses SGP4 and SDP4 as warranted by
    the TLE, I find the following ...
    
     Summary: (taking specific times) (South African Standard Time - UT+2.0 hrs)
     ======================================
                  Greg           Mike          Guide        Matson's Skymap
     Time      az      el       az  el      az      el        Az      El
     ------  ---------------  ----------  ----------------  ---------------
     23:35    231.67  12.76    234  15     236.85  19.35     236.76  19.17
     23:50    318.14  44.15    321  44     324.07  43.01     323.93  42.99
    
    which is within tenths of a degree of your "Guide" results.  Note that,
    according to its documentation, Mike's "program uses a simple 'precessing
    ellipse' model for the predictions..." and "does not use lunar/solar
    perturbations..." which I believe are part of the SDP4 propagation method.
    Mike's "highfly" 
    
    Clear and dark skies!
       Ed Light
    
    Lakewood, NJ, USA
    Site 8840, N 40.1075, W 074.2312, +24 m (80 ft)
    
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