USA 161 post-manoeuvre elements

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Mon Sep 12 2011 - 12:19:11 UTC

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    Russell Eberst, Björn Gimle, Marco Langbroek, Pierre Neirinck, and Scott Tilley contributed observations used to produce
    the following elements:
    
    USA 161                                                  263 X 784 km
    1 26934U 01044A   11255.30275232  .00025734  00000-0  21628-3 0    07
    2 26934  97.8222   9.1129 0377498 193.9089 165.1517 15.13281946    01
    Arc 201109011-0912.32 WRMS resid 0.021 totl 0.012 xtrk
    
    The arc probably is longer than ideal, given the recent spike in geomagnetic activity, but the results appear to be
    reasonably accurate, though perhaps not quite as precise as implied by the residuals.
    
    Yesterday, I finally hit on the correct solution to the observations of Aug 31, Sep 01, Sep 03 and Sep 06: the object
    had manoeuvred to a lower, not a higher orbit. Among the many problems with the higher orbit, was that the plane was
    ~1.3 deg farther east than could be explained by the apparently coplanar manoeuvre(s). The greater eastward rate of
    precession of a lower orbit, of mean motion ~15.15 rev/d, readily accounted for the planar shift, and quickly led to a
    preliminary ~15.13 rev/d solution that fit nearly all of the observations. Scott made the confirming observations last
    night.
    
    It appears that a single manoeuvre was made on Aug 24, near 12-13 h UTC, which decreased the perigee about 40 km, the
    apogee about 120 km, and the argument of perigee about 14 deg. The ground track of the previous orbit repeated after 7
    days (104 revs), the present one after 8 days (121 revs).
    
    All of my earlier estimates of the post-manoeuvre orbit should be discarded.
    
    Ted Molczan
    
    
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