The period of variation of brightness of 99028C / 25746 has decreased steadily ever since it was launched, from about 150 s in 1999 June, to about 89 s in 2005 Aug: http://satobs.org/seesat_ref/99028C_period_of_var/99028C_period_of_var.jpg This plot is based largely on PPAS (Photometric Periods of Artificial Satellites) reports, excluding observations that were obviously indicative guesses. Its decreasing optical period tends to support the consensus that the object is not the payload (99028A / 25744), and most likely debris or a decoy. The strongest evidence is its low area to mass ratio, as evidenced by the significant SRP (solar radiation pressure) orbit perturbation discovered in 2002. That the object rotates at all is further evidence that it is not a high-resolution imager, since those normally are three-axis stabilized. Even if rotation was desired, it would be maintained within a fairly narrow range, unlike the dramatic change we have observed. My guess is that 99028C's slow spin-up may be due to SRP. A similar example may be Midas 6 (63014A / 574), which spun-up for more than 30 years, as shown Fig. 12 on this page: http://www.satobs.org/tumble/expresfpm.html It will be interesting to see how 99028C's period of variation continues to evolve. Ted Molczan ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Wed Jan 25 2006 - 07:40:24 EST
