RE: ISS trailing object

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
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
altitude.

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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