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 ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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