IGS 1A and IB elements

From: Ted Molczan (molczan@rogers.com)
Date: Wed Apr 23 2003 - 10:15:59 EDT

  • Next message: Alan Pickup: "Decay watch: 2003 April 23"

    I have derived the following from observations by David Brierley, Russell
    Eberst, Bjoern Gimle, Petteri Kankaro and Peter Wakelin, received to this
    moment:
    
    Arc 2003 Apr 16 - 22 UTC:
    
    IGS 1A           0.0  0.0  0.0  5.6 v
    1 27698U 03009A   03112.93895354  .00009088  00000-0  35165-3 0    08
    2 27698  97.4064 185.0068 0007340 234.8569 125.1982 15.26215131    08
    
    WRMS residuals = 0.016 deg
    
    Arc 2003 Apr 22 - 22 UTC:
    
    IGS 1B           0.0  0.0  0.0  3.1 v
    1 27699U 03009B   03112.91058181  .00009969  00000-0  41847-3 0    08
    2 27699  97.4129 184.8964 0007790 127.3785 232.8162 15.23479074    09
    
    WRMS residuals = 0.035 deg
    
    IGS 1B manoeuvred on 2003 Apr 22 between 10 h and 11 h UTC, apparently to drop
    its perigee height to near that of IGS 1A:
    
    IGS 1B pre-manoeuvre   497 km x 511 km
    IGS 1B post-manoeuvre  488 km x 512 km
    IGS 1A                 487 km x 496 km
    
    I expect IGS 1B to manoeuvre again at any time, to drop its apogee about 16 km
    to near that of IGS 1A, in order to match its period, to establish a constant
    spacing between the two.
    
    IGS 1A may also be due for a small reboost manoeuvre, which may change its
    mean motion to about 15.259 rev/d. This manoeuvre could happen before and/or
    near the time of IGS 1B's IGS 1A-orbit-matching manoeuvre.
    
    It appears that a very precise 61 rev repeating ground track is to be
    maintained, which will require fairly frequent reboost manoeuvres. If so, then
    over time it may be possible to compute a mean mean-motion that fits a long
    observational arc, facilitating fairly accurate long-term predictions.
    
    Ted Molczan
    
    
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