Re: 99028C: decreasing optical period

From: Bram Dorreman (
Date: Wed Jan 25 2006 - 17:07:21 EST

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    Ted Molczan wrote:
    > 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:
    > 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:
    > It will be interesting to see how 99028C's period of variation continues 
    > to
    > evolve.
    This might be a reason to make it a more important PPAS object.
    So a priority 2 object from now on.
    Also time to change its ID from 1999-028A to 1999-028C (in PROGRAM.ROB).
    Thanks for your alert (or what do you call such a message?)
    (PPAS or BWGS) Bram
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