IGS 1A and IB elements

From: Ted Molczan (molczan@rogers.com)
Date: Mon Apr 28 2003 - 15:20:14 EDT

  • Next message: Alan Pickup: "Decay watch: 2003 April 28"

    I derived the following from observations by David Brierley, Russell Eberst,
    Alberto Rango and myself, received to this moment:
    
    Arc 2003 Apr 26 - 27 UTC:
    
    IGS 1A           0.0  0.0  0.0  5.6 v
    1 27698U 03009A   03117.85770393  .00010000  00000-0  38957-3 0    07
    2 27698  97.4100 189.8871 0008000 141.9297 218.2508 15.25984183    00
    
    WRMS residuals = 0.033 deg
    
    IGS 1B           0.0  0.0  0.0  3.1 v
    1 27699U 03009B   03117.89723933  .00010000  00000-0  39199-3 0    09
    2 27699  97.4104 189.8251 0006546 133.6546 226.5236 15.25787523    04
    
    WRMS residuals = 0.032 deg
    
    On 2003 Apr 27, both Alberto and Russell found IGS 1A running about 9 s late
    relative earlier elsets with mean motion about 15.2613 rev/d. At first, I
    suspected a manoeuvre, but with additional analysis I have concluded that both
    of my points of Apr 27 were at fault:
    
    SCRAPPED 27698 03 009A   2701 G 20030427015540380 17 25 1836150+385037 18 S
    SCRAPPED 27698 03 009A   2701 G 20030427032921230 17 25 0529352+540767 28 7 
    
    Accordingly, I have also scrapped my 15.2613 rev/d elset (epoch
    03117.13637202).
    
    The above IGS 1A elset is for the arc beginning with David's points of Apr 26
    at 21:13 UTC, minus my scrapped points.
    
    Both orbits are now near the 61:4 resonance mean motion, so the initial orbit
    manoeuvres should be about over. There may yet be a small increase in the mean
    motion of IGS 1B, to match that of IGS 1A. That would cause IGS 1B to be early
    by about 11 s per day since epoch.
    
    There will be periodic reboosts. Their frequency depends upon the allowed
    deviation of mean motion from 61:4 resonance, and the rate of decay. My guess
    is that the deviation will be about +/-0.002 rev/d, which at recent rates of
    decay would lead to reboosts about every 3 weeks.
    
    I noticed some tendency toward a slightly higher inclination when fitting the
    orbits, but I will not believe it until there is a longer observational arc,
    so I fixed the values of inclination.
    
    Ted Molczan
    
    
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