99028C: decreasing optical period

From: Ted Molczan (seesat@rogers.com)
Date: Wed Jan 25 2006 - 07:37:20 EST

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    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
    This plot is based largely on PPAS (Photometric Periods of Artificial
    Satellites) reports, excluding observations that were obviously indicative
    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
    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:
    It will be interesting to see how 99028C's period of variation continues to
    Ted Molczan
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