Re: SATOBS ML (4353), 31 May 2014: USA 161

From: C. Bassa via Seesat-l <seesat-l_at_satobs.org>
Date: Sat, 31 May 2014 19:41:32 +0200
Hi Ted, Marco, Bjorn,

I hate to be the bearer of bad news, but I am of the opinion that both
Bjorn and Marco observed IGS 8 r [39063/13002C], not USA 161
[26934/01044A].

These are circular orbit fits against Bjorn and Marco's observations:
Bjorn
1 99999U 14612A   14112.02557292  .00000000  00000-0  50000-4 0    02
2 99999  97.4198 246.6244 0000000   0.0000  60.7336 15.48373684    07
# 20140422.03-20140422.03, 5 measurements, 0.659 deg rms
Marco
1 99999U 14651A   14151.06269994  .00000000  00000-0  50000-4 0    01
2 99999  97.4925 287.4065 0000000   0.0000  53.2450 15.47394948    08
# 20140531.06-20140531.06, 4 measurements, 0.066 deg rms

Propagating the former to the time of the latter yields a RAAN of
286.7120 deg, within a degree of the circular estimate for Marco's
unknown.

Fitting a circular orbit to Leo's unknown from May 24, 2014 gives the
following elset:
1 99999U 14644A   14144.03928469  .00000000  00000-0  50000-4 0    01
2 99999  96.9795 276.4708 0000000   0.0000  56.9491 15.60921888    08
# 20140524.04-20140524.04, 7 measurements, 0.006 deg rms

Propagating this to the observation time of Marco yields a RAAN of 283.3853 deg.

All three objects were seen in similar parts of the sky, indicating
similar parts of the orbit if we neglect the precession of perigee. It
is clear that circular orbit fits to Bjorn and Marco's objects give
similar mean motion and similar inclination, and the nodes are
comparable. Leo's object on the other hand has a different
inclination, mean motion and node.

Taking our elements of IGS 8 r in the timespan from May 11, 2013 until
we lost it on August 31, 2013, it's mean motion increased from 15.3249
revs/day to 15.3543 revs/day. Assuming a linear increase over those
111 days we get a rate of 0.00026415 revs/day per day. Propagating
that rate forward to now would give a mean motion of 15.4266 revs/day.

When we lost USA 161 in the summer of 2013 it had a mean motion of
15.595 revs/day and an inclination of 97.0335 deg. Since it was in a
quite circular orbit we would not expect it to have major changes to
its orbit, hence, Leo's object matches our last know orbit of USA 161.

Finally, IGS 8 r is known to flare wildly, matching the behavior seen
by Bjorn and Marco.

Regards,
    Cees
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Received on Sat May 31 2014 - 12:42:06 UTC

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