USA 116 and 129 elements; manoeuvre forecast

From: Ted Molczan (
Date: Tue Sep 12 2000 - 11:01:28 PDT

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    I have updated the following elements, using observations by David Brierley,
    Russell Eberst, Bjoern Gimle and others, from 03 Aug to 11 Sep UTC:
    USA 116         15.0  3.0  0.0  5.1 v
    1 23728U 95066A   00254.99481481  .00014587  00000-0  33052-3 0    07
    2 23728  97.8869   4.6295 0443117 272.7949  82.2703 14.79531560    00
    USA 129         15.0  3.0  0.0  5.1 v
    1 24680U 96072A   00254.82105903  .00033144  00000-0  47439-3 0    01
    2 24680  97.8720 316.1376 0492500  61.5447 303.4389 14.79067291    05
    Mean residuals of both element sets are less than 1 arc min.
    USA 129's recent small re-boost manoeuvre creates the scenario for major
    re-boost manoeuvres by both objects, within hours of each other, in late
    November or early December.
    On 24 November UTC, USA 129's argument of perigee will be located nearly over
    the equator, creating the first opportunity for the manoeuvres. If the
    manoeuvres do not occur within a day or two of that date, then the next
    opportunity occurs within a day or two of 04 December, when USA 116's argument
    of perigee will be located nearly over the equator.
    I have yet to attempt a sufficiently detailed analysis of past such manoeuvres
    to learn the criteria which determines which of the two dates will be selected.
    Manoeuvres made when perigee is at the equator enable economical,
    single-impulse, changes to several elements. Since both KeyHole orbits cannot
    be over the equator at the same time, I suspect that the manoeuvre date is
    chosen based on the orbit that is most in need of "repair" or which best
    facilitates maintenance of the constellation's RAAN and argument of perigee
    spacings, and orientation with respect to the sun.
    Ted Molczan
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