X-37B OTV 2-1 elements

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Thu May 24 2012 - 12:20:10 UTC

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    Recent observations by Simone Corbellini, Kevin Flanagan, Alexander Repnoy, and myself, revealed/confirmed the object
    was somewhat off track relative earlier search elements. Robert Holdsworth made a valuable observation that confirmed
    the mean motion of ~15.97 rev/d.
    The inclination has been reduced from its original value of 42.798 deg to about 41.9 deg, which increased the rate of
    precession of the ascending node. The manoeuvre(s) that resulted in the present orbit occurred not long after the last
    reported observation of the previous orbit, made by Kevin Fetter on 2012 May 05 UTC.
    Brad Young was the first to spot the object in the present orbit, on May 17. He made three positional observations on
    that and the next night. Brad relied on ObsReduce to locate most of his reference stars, which is a method I promote.
    It's a great method when the main source of prediction error is uncertain rate of decay, but it can result in
    misidentified stars in case of significant orbit manoeuvres. Brad managed to correctly identify the reference stars of
    his first two positions of May 17, but the orbit had changed so much, that ObsReduce led him to the wrong stars of his
    final position of May 17 and all of his May 18 positions.
    I have taken advantage of the improved understanding of the orbit to redo Brad's reductions of the four positions in
    question, and have found the likely reference stars. Below are all of Brad's positions, the final four of which are my
    37375 11 010A   8336 G 20120517022242430 17 25 1348592+162771 58  
    37375 11 010A   8336 G 20120517022248620 17 25 1416871+182667 58  
    37375 11 010A   8336 G 20120517022320940 17 25 1559208+221696 28 S
    37375 11 010A   8336 G 20120518022510040 17 25 1113465+604347 78 S
    37375 11 010A   8336 G 20120518022520120 17 25 1300086+641612 48 S
    37375 11 010A   8336 G 20120518022535890 17 25 1521601+604126 28 S
    Please note that the above correction of the third May 17 position replaces my earlier correction, which turns out to
    have been incorrect. The new estimate remains somewhat in doubt.
    I believe that the following orbit is reasonably accurate, but I am not sufficiently confident in it to issue it with
    the correct identifiers, lest independent archives become polluted with erroneous orbits that could confuse researchers
    in the future.
    X-37B OTV 2-1                                            273 X 299 km
    1 70001U          12145.09446529  .00002255  00000-0  49915-5 0    00
    2 70001  41.8922  80.3446 0019151 318.3243  41.6150 15.96600905    00
    Arc 20120517.1-0524.11 WRMS resid 0.127 totl 0.042 xtrk
    The new orbit causes the ground track to repeat almost precisely, every 3 days (47:3 resonance). The previous orbit
    repeated almost precisely every 2 days (31:2). Ground tracks that repeat at intervals of two, three, or four days, have
    long been favoured for U.S. imagery intelligence satellites, so this may be a clue to the mission of OTV 2-1. OTV 1-1
    also employed repeating ground tracks, most of which repeated at 2, 3 or 4 day intervals, but not as precisely as those
    of OTV 2-1.
    Ted Molczan
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    This archive was generated by hypermail 2b29 : Thu May 24 2012 - 12:20:52 UTC