USA 161 has been recovered

From: Ted Molczan (seesat@rogers.com)
Date: Tue Mar 28 2006 - 17:51:16 EST

  • Next message: Greg Roberts: "Obs 28 March 2006"

    Pierre Neirinck has recovered USA 161 - the primary spacecraft in the KeyHole
    eastern plane. Russell Eberst observed it in the same orbit earlier this month,
    considerably off prediction in time and track, indicative of a major orbital
    manoeuvre. 
    
    Combining their observations:
    
    0104401 2420 20060304 215449.88 175522+452320 6.3 6.3 0 S
    0104401 2420 20060304 215521.27 182723+461645 6.4 6.4 0 S
    26943 01 044A   2563 G 20060326231813570 17 24 2141700+712880 38 S+060 10
    26943 01 044A   2563 G 20060327234439470 17 24 0138610+674752 18 
    26943 01 044A   2563 G 20060327234503150 17 24 0135000+635130 78 
    
    yields the following elements, which have very good residuals (WRMS = 0.023
    deg):
    
    USA 161         15.0  4.0  0.0  5.2 v                    306 X 982 km
    1 26943U 01044A   06086.97644047  .00003942  00000-0  79458-4 0    02
    2 26943  97.9694 195.1640 0481213 208.7754 148.6124 14.74335526    04
    
    The new orbit is more eccentric that the previous one: perigee is nearly 100 km
    lower, and apogee is nearly 100 km higher:
    
                                                             403 X 885 km
    1 26934U 01044A   06010.86341370  .00001200  00000-0  68132-4 0    02
    2 26934  97.9180 120.2251 0343693  94.7482 265.2517 14.74446208    03
    
    The previous orbit had been something of a mystery. In 2001 October, the
    spacecraft was launched into the usual 260 x 1019 km orbit, but in 2002 Jan, it
    unexpectedly manoeuvred to a 405 X 857 km orbit, and has manoeuvred infrequently
    ever since.
    
    Why propellant would have been expended to greatly lower USA 161's eccentricity
    in 2002, only to reverse the process in 2006 is unclear. Perhaps it was intended
    to decrease drag, to conserve propellant, until the eventual launch of USA 129's
    successor, in the western KeyHole plane, which occurred in fall of 2005, with
    the launch of USA 186.
    
    Bjorn Gimle recently recovered both of those spacecraft:
    
    USA 129         15.0  4.0  0.0  5.3 v
    1 24680U 96072A   06086.82390126  .00006337  00000-0  81610-4 0    07
    2 24680  97.8693 150.9730 0545274 324.0655  32.4996 14.69913709    03
    
    USA 186         15.0  4.0  0.0  5.3 v
    1 28888U 05042A   06083.83893398  .00009500  00000-0  96176-4 0    03
    2 28888  97.8564 146.8856 0545537  39.7754 320.2244 14.74232473    01
    
    USA 129 was found to have manoeuvred on 2006 Mar 16 UTC, raising its apogee more
    than expected to maintain the standard synchronization of ascending node
    crossing time between the western and eastern KeyHoles. 
    
    USA 186 has not manoeuvred since it was launched; however as a result of USA
    161's recent manoeuvre, the two appear to be synchronized. 
    
    So, it would appear that the baton has been passed from USA 129 to USA 186. It
    will be interesting to see whether or not USA 129 and USA 116 (95066A / 23728)
    (the backup eastern plane KeyHole) re-establish some sort of synchronized
    relationship.
    
    Ted Molczan
    
    
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