USA 269 observations and orbit analysis

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Fri, 12 Aug 2016 20:13:15 -0400
I apologize of the lateness of this report.

Paul Camilleri observed and imaged USA 269 (16047A / 41724) on 2016 Aug 11 UTC. It was in a 5 deg inclined orbit, at its
apparent initial GEO destination, 92 deg E longitude.

Cees Bassa performed all of the data reduction of Paul's imagery, on which he found several other satellites of interest
to the group, including an UNID that is in a very similar orbit to that of USA 269. I have appended all of the reduced
data.

Cees fit the following nearly synchronous circular orbit to USA 269:

USA 269                                              35786 x 35795 km
1 41724U 16047A   16224.69522568  .00000000  00000-0  00000-0 0    07
2 41724   5.0086 327.6383 0001000   0.0000 335.2639  1.00260530    00
# 20160811.67-20160811.72, 70 measurements, 0.004 deg rms

Additional observations are required to determine an accurate orbit.

USA 269 was steady in brightness, an indication that it had ceased the 0.25 RPM roll it had been in while in its
transfer orbit, and was now 3-axis stabilized.

The UNID, to which Cees has assigned the (hopefully) temporary ID 16724B / 99503, was also steady, but less bright than
USA 269. Cees estimated 11.5 magnitude. He fit the following circular elements:

Unknown 160811B                                      35829 x 35837 km
1 99503U 16724B   16224.70153368  .00000000  00000-0  00000-0 0    07
2 99503   5.0642 325.1394 0001000   0.0000 350.3988  1.00107933    03
# 20160811.66-20160811.74, 22 measurements, 0.005 deg rms

The observational arc was too short to constrain a reliable solution, but the real orbit probably was not radically
different. Cees and I have compared this orbit and the underlying observations against the orbits of all satellites
known to us, including those in the most recent available ISON dataset, and found no matches.

As Cees pointed out, and is plainly evident, the UNID and USA 269 have similar RAAN and inclination (their planar
separation is just 0.2 deg), which raises the question of a possible relationship between them.

Mike McCants made a preliminary investigation of that possibility, by means of a "conjunction analysis." He
assumed that USA 269 made a couple of maneuvers from its last known orbit to reach 92 E and go synchronous there. He
found that the final maneuver would have been at some time on or after Aug 8 (day 221) at 0600 UT. He found that if the
UNID separated at that time, then the following elements would intersect with the orbit of USA 269 and fit the data
reduced from Paul's imagery of Aug 11 UTC:

                                                     35400 X 35769 km
1 99503U 16724B   16224.70218182  .00000000  00000-0  00000-0 0    03
2 99503   5.0642 325.3294 0044000 177.0000 173.3988  1.01000000    07

Inspired by Mike, I concocted a similar orbit, but based on arrival at GEO about 12 h later:

                                                     35244 X 35789 km
1 99503U 16724B   16224.70153368  .00000000  00000-0  00000-0 0    07
2 99503   5.0349 325.4248 0065000 135.1634 215.3754  1.01247585    01

Perhaps the UNID will be recovered near one of the above three orbits that we have estimated. Allowance should be made
for considerable along-track error.

We caution that the apparent correlation between the UNID and USA 269 may prove to be a meaningless coincidence between
unrelated objects.

Ted Molczan


11397 79 053A   8600 G 20160811174049994 27 25 2142163+042144 17 I
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11397 79 053A   8600 G 20160811174530016 27 25 2146843+044059 17 I
11397 79 053A   8600 G 20160811174629978 27 25 2147596+044374 17 I
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41724 16 047A   8600 G 20160811160905029 27 25 1912320+020412 17 S
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99503 16 724B   8600 G 20160811155345042 27 25 1941209+024928 17 S
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99503 16 724B   8600 G 20160811174320006 27 25 2130539+051993 17 S
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99503 16 724B   8600 G 20160811174609997 27 25 2133356+052349 17 S
99503 16 724B   8600 G 20160811174619978 27 25 2133545+052408 17 S
99503 16 724B   8600 G 20160811174639978 27 25 2133843+052417 17 S


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Received on Fri Aug 12 2016 - 19:14:00 UTC

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