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 ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
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