Lacrosse 2 may have been de-orbited

From: Ted Molczan (
Date: Thu Mar 31 2011 - 10:56:34 UTC

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    Russell Eberst has reported that the Lacrosse 2 (91017A / 21147) radar imagery intelligence satellite was missing from
    its predicted path last night, 2011 Mar 30 near 20:40 UTC, so it is possible that it has changed its orbit, or even been
    The last reported observation was by Pierre Neirinck, on Mar 24, near 21:33 UTC. Brad Young also observed it on the
    24th, at about 01:55 UTC.
    If any one has either seen or not seen it between Pierre's observation and Russell's non-observation, it would be useful
    to know the date and time. If seen, please state whether it appeared to be on-time. That would help narrow the time of
    its apparent orbit manoeuvre.
    The object has a history of small orbit changes that increase or decrease its period by a fraction of one second, more
    likely the result of momentum wheel unloading manoeuvres than intended orbit manoeuvres. Had it made such a manoeuvre
    shortly after it was last observed, then last night it could have been early or late by at least 30 s, up to 1 or 2 min.
    If so, then even if it passed earlier than expected, I suspect Russell would have had time to recover it; however, a
    larger orbit change cannot be ruled out, and given the object's age, it could well have been de-orbited.
    It is a reliable magnitude 2 or 3 object on favourable passes, so it will not be difficult to determine whether it
    remains in orbit. In case its mean motion changed more than usual, I suggest looking for it within +/- 10 min of
    prediction, with allowance for Earth's rotation. If it is not seen eventually, then we will be able to safely conclude
    that it has been de-orbited.
    This is the last known orbit:
    Lacrosse 2
    1 21147U 91017A   11083.88616256  .00000250  00000-0  35917-4 0    07
    2 21147  67.9850 102.4518 0005000 214.0069 145.9930 14.76331375    01
    Happy hunting!
    Ted Molczan
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