89001K - an interesting SRP perturbation object

From: Ted Molczan (molczan@home.com)
Date: Thu Feb 08 2001 - 09:37:09 PST

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    On 2001 Jan 14, Russell Eberst observed a single point of an unknown object.
    Mike McCants, Bjoern Gimle and I found that 89001K / 25798 passed close to
    Russell's point at the observed time.
    
    I was reluctant to declare a positive identification based on that one point,
    because the residual was greater than normal for Russell, and because the
    object was several orders of magnitude brighter than expected, based on
    89001K's small RCS. I have since become convinced that the object is indeed
    89001k, based upon Russell's additional observations, and a review of the
    object's orbital history.
    
    Through 2001 Feb 06, Russell observed 89001K on 4 passes, and reported 7
    points. I estimate the standard magnitude to be about 5.6 on average, which
    confirms that the object is much brighter than its small RCS implies.
    
    A review of its orbital history revealed that 89001K is fairly sensitive to SRP
    (solar radiation pressure) perturbation. This is the same force that is the
    basis of Solar Sail propulsion concepts.
    
    Since it was catalogued in mid'1999, its inclination has varied between about
    64.37 deg to 65.02 deg.
    
    Its eccentricity has varied between about 0.454 and 0.495, causing the perigee
    and apogee to oscillate over a range of more than 400 km.
    
    I estimate that 89001K's area to mass ratio is between about 1 and 10 m^2/kg,
    probably closer to the low end of the range.
    
    NORAD's SGP4 orbital model does not include SRP perturbations, resulting in
    elements of lower than usual accuracy. That accounts for the unusually high
    residual that I noted in Russell's first sighting, when the object was still an
    unknown. In fact, all of Russell's subsequent points also have large residuals
    relative to the nearest NORAD elements. If, as I suspect, NORAD is using a long
    data arc (i.e. the time span of the observations) then the accuracy degradation
    due to SRP is exacerbated.
    
    Of course, it probably is not worth increasing the tasking (NORAD-speak,
    roughly meaning observational priority), given that the object is a small piece
    of debris, that is not near decay, and would not survive decay. Also, its
    perigee is usually well above the orbits of the most important LEO satellites,
    i.e. ISS, Mir, Shuttles, HST, Lacrosses, KeyHoles.
    
    I have compiled a 151 element set orbital history from Allen Thomson's large
    elset files. I will be pleased to e-mail the history to anyone who requests it.
    
    Here are recent elements, in case anyone wishes to observe 89001K:
    
    89001K           0.8  0.0  0.0  5.6 v 0.46
    1 25798U 89001K   01038.44556507  .00002746  00000-0  42355-1 0  5352
    2 25798  64.9435 287.3983 4614102 128.9700 282.1398  5.53006008 41273
    
    If observers can produce large numbers of obs over periods of a few days, then
    it should be possible to improve upon the accuracy of NORAD's orbits. I am not
    suggesting that this be done, but if large numbers of obs should become
    available, then I will make every effort to produce elements (time permitting.)
    
    It may also be worth checking some of the other 89001 debris for signs of SRP
    sensitivity.
    
    Ted Molczan
    
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