Re: The perils of relying on TLEs

From: wintermute@pcisys.net
Date: Mon Oct 18 2004 - 15:10:39 EDT

  • Next message: paul: "video time inserter info"

    With all due respect to the original authors, performing collision 
    avoidance analysis with 30 day old data is an exercise in futility.  TLE 
    data is marginal at best for this type of analysis.  At that age, even 
    without the noted inconsistencies, it would be next to worthless. 
     
    To be worthwhile, such an assesment needs to be statistically qualified.  
    Miss distance alone is not a good indicator of collision risk. 
     
    > >OPERATIONAL EXPERIENCE OF THE USE OF A GENERIC PRODUCT FOR COLLISION 
    RISK 
    > >ASSESSMENT ON GEOSTATIONARY ORBIT 
    >  
    > http://www.issfd.dlr.de/papers/P1080.pdf 
    >  
    > >when five close approaches to GOES-7 were detected in a period of 3 
    days 
    >  
    > 1 17561U 87022A   04050.46768113  .00000058  00000-0  10000-3 0  3186 
    > 2 17561   8.3108  53.3103 0001830  57.4809  31.4127  1.00288558 45411 
    >  
    > The above elset is consistent with the previous elsets. 
    >  
    > 1 17561U 87022A   04061.98466440  .00000078  00000-0  00000+0 0  3304 
    > 2 17561   8.3140  53.2970 0000200 292.7340 354.9150  1.00248806 45525 
    >  
    > This one is not. 
    >  
    > 1 17561U 87022A   04078.59653115  .00000062  00000-0  00000+0 0  3512 
    > 2 17561   8.3613  53.1063 0001725  52.8809 111.0617  1.00288986 45691 
    >  
    > This one is consistent. 
    >  
    > The authors admit that such cases are "rare". 
    >  
    > "An upgrade is being studied to perform historical analysis of the TLE 
    > data and, in this way, detect the potential strange events by 
    inspection 
    > of the TLE file used, warning the user of such potential problems." 
    >  
    > Reference 9: Discussion of SDP4 problems by Rob Matson on SeeSat 
    > in March, 1997. 
    >  
    > ----------- 
    >  
    > For GOES 7, there is a "discontinuity" between these two elsets: 
    >  
    > 1 17561U 87022A   04145.37495207  .00000126  00000-0  00000+0 0  4230 
    > 2 17561   8.4814  52.6007 0006038 103.2954  57.6503  1.00323582 46367 
    >  
    > 1 17561U 87022A   04160.00000000 +.00000046 +00000-0 +00000-0 0 04412 
    > 2 17561 008.5213 052.4427 0003740 037.8302 348.7438 01.00276230046516 
    >  
    > There is then one inconsistent elset: 
    >  
    > 1 17561U 87022A   04177.78841676  .00000076  00000-0  00000+0 0  4600 
    > 2 17561   8.5614  52.3749 0002910  44.8066 286.1292  1.00230307 46686 
    >  
    > Subsequent elsets are consistent: 
    >  
    > 1 17561U 87022A   04196.00000000  .00000086  00000-0  00000+0 0  4807 
    > 2 17561   8.6029  52.3013 0003140  55.3166  12.1764  1.00289224 46879 
    >  
    > There is a similar "jump" in early 2003: 
    >  
    > 1 17561U 87022A   03013.52827387  .00000116  00000-0  10000-3 0  8102 
    > 2 17561   7.5470  55.7264 0004064 288.6625 149.4031  1.00317770 41389 
    >  
    > 1 17561U 87022A   03039.31434324  .00000057  00000-0  10000-3 0  8443 
    > 2 17561   7.5828  55.6050 0005340 259.6270 117.9254  1.00250703 41648 
    >  
    > So it appears that GOES 7 is still being controlled in longitude 
    > (over a very large range of longitudes). 
    >  
    > Mike McCants 
    >  
    > 
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