RE: X-37B OTV 3 search elements

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Wed Dec 12 2012 - 01:30:33 UTC

  • Next message: ronlee@pcisys.net: "ISS in shadow and another brilliant UNI"

    Greg Roberts provided me with a several images from his video, from which I reduced the following data using ObsReduce:
    
    79211 12 071A   0433 G 20121211184019516 17 25 1847070-573065 37 S
    79211 12 071A   0433 G 20121211184043692 17 25 1802812-691653 37 S
    79211 12 071A   0433 G 20121211184102992 17 25 1628966-771729 37 S
    79211 12 071A   0433 G 20121211184103992 17 25 1620966-773728 37 S
    79211 12 071A   0433 G 20121211184126158 17 25 1230355-790619 37 S
    79211 12 071A   0433 G 20121211184127158 17 25 1221034-785409 37 S
    
    The arc is fairly short, so there is some uncertainty in the orbit. I offer three possible solutions, that I hope
    bracket the actual orbit.
    
    I began my analysis assuming a fairly circular orbit, and obtained this result (epoch is at final observation):
    
    OTV 3 roughly circular                                   360 X 374 km
    1 79211U 12071A   12346.77878473  .00005681  00000-0  50000-4 0    00
    2 79211  43.6470 137.5456 0010000 255.3229 354.1110 15.67784569    09
    
    The residuals are decent, but they seem to trend higher as the pass proceeds, which leads me to believe that the
    inclination and eccentricity may be a bit off. The following somewhat more eccentric orbit is a much better fit (epoch
    is at final observation):
    
    OTV 3 after MECO1                                        340 X 460 km
    1 79212U 12071A   12346.77878472  .00004344  00000-0  50000-4 0    05
    2 79212  43.5000 136.9474 0088290 298.0881 312.5233 15.56295322    01
    
    I tried many variants of this solution, all of which tended toward inclination 43.5 deg +/- 0.02, so I fixed it at 43.5
    exactly. I am comforted a bit, knowing that this result happens to yield altitude at MECO1 within a few kilometres of
    the values heard on the launch commentary.
    
    First apogee of the above orbit occurred over the western U.S.A., within range of the AFSCN sites at VAFB and Colorado,
    which is where I suspect the perigee would have been raised, yielding something like the following (epoch is estimated
    time of ignition):
    
    OTV 3 circularized                                       439 X 460 km
    1 79213U 12071A   12346.82010417  .00004344  00000-0  50000-4 0    09
    2 79213  43.5000 136.7055 0016000 298.3593 184.0225 15.39500000    04
    
    Given the shortness of the arc, and the considerable guesswork underlying the 79213 TLE, the safest search strategy
    would be to plot all three of the above orbits, and bracket between them. It's more work, but improves the probability
    of success.
    
    Northern hemisphere observers as far north as about 44 N have morning visibility.
    
    Happy hunting!
    Ted Molczan
    
    
    _______________________________________________
    Seesat-l mailing list
    http://mailman.satobs.org/mailman/listinfo/seesat-l
    



    This archive was generated by hypermail 2b29 : Wed Dec 12 2012 - 01:32:04 UTC