NROL-49 search elements

From: Ted Molczan (
Date: Thu Jan 20 2011 - 20:02:27 UTC

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    NROL-49 is scheduled for launch on a Delta 4 Heavy, from VAFB, today (2011 Jan 20), during a 15 min
    window beginning at 21:08 UTC.
    It will launch a KeyHole imagery intelligence satellite of KH-11 lineage, which will replace a
    similar satellite in the standard eastern KH plane: USA 161 (01044A / 26934), launched from VAFB on
    a Titan 4B, in October 2001.
    Accurately estimating KH orbits pre-launch is complicated by uncertainty about the planned argument
    of perigee of their moderately eccentric (for LEO) orbits. There are two standard KH planes, with
    nodes separated about 49 deg, and argument perigee separated by roughly 90 to 180 deg.
    I have experimented with several different arguments of perigee, ranging from 141 deg to 244 deg,
    and settled on 141 deg, but its just a guess, and on past launches I have generally guessed wrong by
    tens of degrees.
    The second stage rocket body apparently will be de-orbited on the first rev; the centre of the
    debris footprint is on the equator, near 152 W. I have taken that into account in guessing the
    argument of perigee, since the de-orbit should be roughly at apogee.
    I have also guessed that the extraordinary performance of the Delta 4 Heavy will be used to insert
    the spacecraft into its standard ~270 km perigee, instead of the past practice (with Titan 34D and
    Titan 4), which was to insert into ~150 x 1000 km, and have the spacecraft raise its perigee.
    I have assumed that the plane will match that of USA 161, but it could easily differ by a degree or
    The following elements are based on launch at window-open:
                                                            272 X 1038 km
    1 72001U          11020.91666667  .00000000  00000-0  00000-0 0    04
    2 72001  97.9000 135.1374 0545000 140.9173 179.6287 14.71000000    03
    In the event the launch is delayed, I will post an update.
    Prediction time error during the first few hours is likely to be several minutes. Track error could
    be quite large, due to the uncertainty in argument of perigee.
    If the argument of perigee is correct, then southern hemisphere observers around 35 S or so, will
    have middle of the night visibility. But if I am way off - for example, should it match the argument
    of perigee of USA 161, then the orbit will be in eclipse.
    Happy hunting!
    Ted Molczan
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