[amsat-bb] Marked differences in published elements?

[Ka8syx2003@xxxxxxx]

Folks,

Because I've been between home qths lately, I haven't had opportunity to be 
QRV, but was poking around on the computer this evening.  During past QSOs with 
some of you, I've mentioned that I pull all of my predictions from WinOrbit 
3.6 to printed ephemeris and hand carry them outside where I set up for a given 
pass.  Tonite I made side by side comparisons between the predictions I was 
getting off of Satscape 2.02 pro and off the WinOrbit.  I like Satscape because 
it provides some "sexier" views and is more "real-time" feeling.  Anyhow, I 
was watching what FO-29 was doing this evening during an approximately 0140 to 
0200 pass on both programs and discovered marked differences in predicted 
location, variances of several degrees in alt, az and lat/lon subsatellite point.  
Comparing the elements that I routinely download from AMSAT with those the 
Satscape took via "internet update" from Celestrak illustrated a possible cause 
of the differences:

DECODE 2-LINE ELSETS WITH THE FOLLOWING KEY:
1 AAAAAU 00  0  0 BBBBB.BBBBBBBB  .CCCCCCCC  00000-0  00000-0 0  DDDZ
2 AAAAA EEE.EEEE FFF.FFFF GGGGGGG HHH.HHHH III.IIII JJ.JJJJJJJJKKKKKZ
KEY: A-CATALOGNUM B-EPOCHTIME C-DECAY D-ELSETNUM E-INCLINATION F-RAAN
G-ECCENTRICITY H-ARGPERIGEE I-MNANOM J-MNMOTION K-ORBITNUM Z-CHECKSUM

AMSAT.ORG (05181.AMSAT)
FO-29
1 24278U 96046B   05181.59521482  .00000020  00000-0  53797-4 0  9873
2 24278 098.5427 229.3523 0351282 141.4784 221.1994 13.52914251438002

www.celestrak.com/NORAD/elements/amateur.txt
FO-29                   
1 24278U 96046B   05184.18367414 -.00000027  00000-0  60488-5 0  9890
2 24278  98.5431 231.5914 0351209 134.7619 228.2674 13.52913791438356

There are some big variations between the two sets.  I realize that the AMSAT 
numbers are for Julian 05181 and the Celestrak figures are apparently three 
days fresher, but can that small difference (when the Satscape launchpad 
suggests a user only needs to correct/update his keps once a month or at most 
frequently every few weeks) cause such wide discrepancies?

Which can I believe?  Being an older app, should I just toss WinOrbit 3.6 out 
in favor of the Satscape?  As a control, I also compared both realtime 
predictions, as they were occurring, with NASA J-Pass 2.0's prediction for this same 
pass of FO-29 and its figures came much closer to the Satscape predictions.  
All other parameters (geo location of observer, etc.) were identical within a 
few thousandths of a degree and of similar precision.

Comments, replies, am I just doing something wrong?  Thanks for any offered 
insights!
73, Ray KA8SYX
Jacksonville, FL EM90ee (formerly of Big Pine Key, FL EL94hr ;>)
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