USA 224 and Elisa search elements

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Thu Mar 14 2013 - 17:46:09 UTC

  • Next message: Ted Molczan: "USA 236 search elements"

    Overnight, Cees Bassa observed a couple of unknowns, which are the basis for the following elements.
    
    I agree with Cees that the following observations correlate with USA 224:
    
    99044 13 572B   4553 E 20130313223512918 17 25 1812020+470670 37 I
    99044 13 572B   4553 E 20130313223522897 17 25 1822663+474845 37 I
    99044 13 572B   4553 E 20130313223532897 17 25 1833414+482522 37 I
    99044 13 572B   4553 E 20130313223542897 17 25 1844370+485679 37 I
    
    I arrived at the search TLE below by the following steps. I zeroed the rate of decay of the last known TLE (epoch
    12236.01577912) and adjusted its mean motion to approximate last night's observations. Since the orbit is
    sun-synchronous, I accounted for solar gravity in the interim by propagating the adjusted TLE to the present using Mike
    McCants' int2. Finally, I used a differential corrector to adjust only RAAN and mean anomaly to minimize the residuals,
    then inserted my guess as to rate of decay.
    
    USA 224
    1 70001U          13072.92776423  .00021830  00000-0  20000-3 0    03
    2 70001  97.9183 186.3421 0532071 241.3390 113.3346 14.78878500    01
    
    The residuals are very small, but the mean motion and rate of decay are uncertain. The predicted time is accurate to
    perhaps 1 or 2 min per 24 h from epoch.
    
    Cees suspected that his 99043 could be IGS 5A (09066A / 36104), but it correlates more closely with Elisa W11 (11076A /
    38007) and Elisa W23 (11076C / 38009), running about 30.5 min early relative the epoch 12280.86155782 11076A TLE. It
    seems a bit closer to 11076A, but additional observations are required to decide, and it will help to find its
    companion.
    
    If the Elisa group has manoeuvred higher since they were last observed, then Cees's circular approximation is a good
    basis for searching:
    
    1 99043U          13072.88907837  .00002304  00000-0  50000-3 0    08
    2 99043  98.3082 149.6661 0010000   0.0000  66.4573 14.58174503    00
    
    Here is an alternative, in case it has merely decayed at a faster rate than it had been, derived using the same
    procedure as for 11002A:
    
    1 70002U          13072.87651484  .00001106  00000-0  21299-3 0    02
    2 70002  98.1450 149.0457 0001671  82.1452 277.9940 14.63630506    07
    
    If it is not in the 70002 orbit, then it should follow shortly in the 99043 orbit.
    
    Ted Molczan
    
    
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