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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