RE: NROL-76 elements from observations

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Fri, 26 May 2017 10:18:16 -0400
The following elements have been derived from observations by Leo Barhorst, Kevin Fetter, Sergey Guryanov, David
Hopkins, Marco Langbroek, Alberto Rango, Scott Tilley, Brad Young, and Mike Waterman:

USA 276                                                  390 X 410 km
1 42689U 17022A   17146.05615742  .00004806  00000-0  66833-4 0    01
2 42689  49.9996 154.4553 0014810  91.7985 268.4680 15.56142385    01
Arc 20170523.76-0526.08 WRMS resid 0.054 totl 0.015 xtrk

As Marco Langbroek alerted yesterday, USA 276 will pass within tens of kilometres of ISS on Jun 3, unless either one
changes its orbit. Below is some data for the closest approaches with range <= ~100 km.

                   ISS sub-satellite point     USA 276 sub-sat point
                  -------------------------  ------------------------- 
  TCA      Range    Lat      Lon      Alt      Lat      Lon      Alt
  UTC       km      deg      deg      km       deg      deg      km
11:43:23  108.21  40.83 N 175.53 E   409.80  41.58 N 174.78 E   392.25
12:29:18   76.52  43.77 S  21.97 W   418.32  44.07 S  22.77 W   422.85
13:15:46   45.60  43.44 N 146.97 E   410.63  43.64 N 146.56 E   392.83
14:01:55   12.32  43.75 S  45.45 W   418.30  43.79 S  45.57 W   422.75
14:48:08   28.98  43.92 N 122.40 E   410.80  43.81 N 122.62 E   392.89
15:34:32   53.59  43.72 S  68.93 W   418.28  43.51 S  68.38 W   422.65
16:20:31   89.38  44.36 N  97.89 E   410.95  43.95 N  98.76 E   392.95
17:07:08  118.38  43.73 S  92.49 W   418.27  43.26 S  91.28 W   422.55

The time and range of closest approach is fairly sensitive to the decay rate of USA 276, which may not yet have settled
down to its actual value, due to the still short observational arc.

After each conjunction, the objects move apart, typically reaching a range of around 400 km, before closing in for the
next encounter.

I have not made a close evaluation of visibility. A cursory review of the above does not reveal favourable observing
circumstances for any of the regular contributors to the list.

For USA 276, I used the above TLE. For ISS, I used NASA's current estimated TLE for June 3:

https://spaceflight.nasa.gov/realdata/sightings/SSapplications/Post/JavaSSOP/orbit/ISS/SVPOST.html

1 25544U 98067A   17154.59567142  .00016717  00000-0  10270-3 0  9127
2 25544  51.6394 106.0762 0004802 233.4052 126.6659 15.53976959 19638

Ted Molczan


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Received on Fri May 26 2017 - 09:19:06 UTC

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