USA 193 elements from observations

From: Ted Molczan (molczanseesat@rogers.com)
Date: Fri Feb 02 2007 - 10:43:28 EST

  • Next message: Dale Ireland: "RE: USA-179/90027"

    The following takes advantage of new obs by Pierre Neirinck and Alberto Rango:
    
    USA 193          5.0  2.5  0.0  4.2 v
    1 29651U 06057A   07032.74187113  .00024388  00000-0  18744-3 0    00
    2 29651  58.5084 270.1113 0008773 105.8866 254.3187 15.71460936    01
    Arc 2007 Jan 27.73 - Feb 01.76, WRMS residuals = 0.023 deg
    
    Also, I have added David Brierley's Jan 31 observation to my epoch Jan 31
    solution, resulting in this revision:
    
    1 29651U 06057A   07031.72396058  .00018870  00000-0  14550-3 0    07
    2 29651  58.5076 274.5066 0008327 109.7698 250.4286 15.71389816    02
    Arc 2007 Jan 25.76 - 31.74, WRMS residuals = 0.019 deg
    
    I am now confident that the orbit is more or less frozen. An exact frozen orbit
    of USA 193's inclination and mean motion would have its argument of perigee
    oscillating near 90 deg, and its mean eccentricity (i.e. stated at arg perigee
    zero) oscillating near 0.0009458. 
    
    The following plot of observed argument perigee vs. time, derived from
    observations by my fellow hobbyists, reveals essentially zero correlation with
    time, with a mean value near 100 deg, and some indication of an oscillation.
    
    http://satobs.org/seesat_ref/06057A/USA_193_w_vs_time.jpg
    
    The normal rate of precession of the argument of perigee would have been about
    1.4925 deg/d. To illustrate the degree of departure from a normal orbit, I have
    plotted normally precessing arg of perigee, relative 100 deg at elapsed time
    zero, and 100 deg at elapsed time 47.5 d.
    
    The following plot of observed mean eccentricity vs. time, derived from
    observations by my fellow hobbyists, reveals a value near 0.0009, and some
    indication of an oscillation.
    
    http://satobs.org/seesat_ref/06057A/USA_193_ecc_vs_time.jpg
    
    Frozen orbits have long been a feature of remote sensing missions that require
    precise data on spacecraft altitude, including most radar altimeters and SARs
    (synthetic aperture radars), radiometers, and some optical imagers, e.g. SPOT
    and Landsat. If USA 193's frozen orbit was intentional, then it would indicate
    some sort of a remote sensing mission, e.g. optical or radar IMINT.
    
    In closing, on a different subject, here is an update of the standard magnitude
    plot:
    
    http://satobs.org/seesat_ref/06057A/06057A_stdmag_3.jpg
    
    Ted Molczan
    
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