RE: ISS trailing object

From: Ted Molczan via Seesat-l <>
Date: Tue, 9 May 2017 17:29:25 -0400
Ron asked:

> Did anyone figure out what the unidentified object was trailing along with
> ISS I observed on Monday Morning?

Several of us have been discussing your mystery object off-list, aided by the additional information that you provided.
I caution that the following is very preliminary and could prove to be without merit.

It does not appear to be any object that we know. NROL-76 launched into a plane that was in the vicinity of ISS. It
probably did not target the orbit of ISS, but as Cees Bassa pointed out, since ISS is a popular target, its close
proximity to that orbit could result in serendipitous sightings.

If your mystery object is related to NROL-76, then its plane is quite a bit west of where it would have been expected,
based on the circumstances of the launch. I have been experimenting with various orbits that could fit your sighting and
correlate with NROL-76.

Something around 48 deg inclination seems to fit. To align with the RAAN of ISS would have required a large manoeuvre
near the northern or southern apex of the orbit, which appears to be within the capability of the launch vehicle, with a
substantial payload. Interestingly, the resulting orbit would have roughly matched the plane of the stage 2 de-orbit
trajectory, implied by the time, location and orientation of the NOTAM co-ordinates.

Below are a few approximate orbits that closely approximate your sighting:

                                                         328 X 335 km
1 74401U          17128.36666670  .00000000  00000-0  00000-0 0    08
2 74401  48.0000 230.8000 0005000 209.7698 205.8000 15.80000000    08
                                                         357 X 363 km
1 74402U          17128.36666669  .00000000  00000-0  00000-0 0    07
2 74402  48.0000 231.2000 0005000 209.7698 205.4000 15.70000000    09
                                                         412 X 418 km
1 74403U          17128.36666668  .00000000  00000-0  00000-0 0    07
2 74403  48.0000 231.9700 0005000 209.7698 204.3674 15.50980000    04

The 74401 orbit would have been near eclipse at the time of your sighting, so it is the approximate lower bound of

I am far from confident that your mystery object is related to NROL-76, but it seems a possibility.

Ted Molczan

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Received on Tue May 09 2017 - 16:29:58 UTC

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