RE: UNID 21-07-2020

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Fri, 24 Jul 2020 09:36:49 -0400
I want to add that Cees also observed 18084C / 43673 as an UNID, less than two minutes after Leo observed it. The
mystery was solved over a period of nearly 24 hours, involving a dozen e-mails. At one point it seemed that both
observers had seen the same object. But doubts arose, and this idea was rejected. Eventually it was revived and
confirmed, but our final e-mails were not consistently clear on that point.

Cees was the first to report his observations of the night of July 21/22. He noted that "Unknown 99565/20703A gave a
flash on top of a longer flare. It's path correlates to that of the 46 day old TLE of Essaim 2 [28495/04049D]".

http://satobs.org/seesat/Jul-2020/0114.html

99565 20 703A   4171 G 20200721231858094 17 25 0340406+534358 37 I
99565 20 703A   4171 G 20200721231858854 17 25 0342174+534884 37 I
99565 20 703A   4171 G 20200721231859613 17 25 0343912+535374 37 I
99565 20 703A   4171 G 20200721231900233 17 25 0345357+535765 37 I

It seemed a very good match, so Mike used the observations to update the elements of Essaim 2, issuing a TLE with epoch
20203.96014754.

Hours later, Leo reported his observations of the night of July 21/22, which included an UNID that he correlated with
11050A / 37813.

http://satobs.org/seesat/Jul-2020/0116.html

Mike disagreed with that correlation. I wondered what Leo might actually have seen.

The following is a summary of how Mike and I solved the mystery: 

An orbit of 97.9 deg inclination and 14.9 rev/d mean motion could be fit to Cees's plus Leo's observations, indicating
that that they may have observed the same object. But this orbit did not make sense for Essaim 2. There was also
considerable doubt that they had observed the same object.

For a time, it appeared that the only way to resolve the matter would be to check whether anything is present in Mike's
Essaim 2 orbit of epoch 20203.96014754 or in the disputed 14.9 deg orbit. 

Further investigation revealed that several objects from the 2018-084 launch were in orbits near 97.9 deg inclination
and 14.9 rev/d mean motion, which were not far in plane from the UNIDs observed by Cees and Leo. The only one for which
the USAF did not have current elements was 18084C / 43673. Its latest TLE was about 9 days old. Jonathan McDowell's
satellite catalogue identifies it as a lower fairing half. It happened to correlate almost perfectly with the
observations of interest, but was running a few minutes late. This could be explained by a breakup, which turned out to
have been what happened. End of mystery.

Mike has withdrawn the Essaim 2 TLE of epoch 20203.96014754, and it should be deleted from personal archives.

Leo's correctly identified observations are:

43673 18 084C   0796 E 20200721231707236 17 25 0056565+344406 37 F
43673 18 084C   0796 E 20200721231712240 17 25 0103294+363214 37 S
43673 18 084C   0796 E 20200721231716482 17 25 0109302+380088 37 F
43673 18 084C   0796 E 20200721231722478 17 25 0118153+400596 37 S

Likewise, Cees's observations are:

43673 18 084C   4171 G 20200721231858094 17 25 0340406+534358 37 I
43673 18 084C   4171 G 20200721231858854 17 25 0342174+534884 37 I
43673 18 084C   4171 G 20200721231859613 17 25 0343912+535374 37 I
43673 18 084C   4171 G 20200721231900233 17 25 0345357+535765 37 I

Ted Molczan


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Received on Fri Jul 24 2020 - 08:37:59 UTC

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