OTV 3 post-manouevre elements and a small mystery

From: Ted Molczan via Seesat-l <seesat-l_at_satobs.org>
Date: Sat, 9 Aug 2014 11:09:39 -0400
The following TLE is derived from observations last night, reported by Kevin Fetter, Alberto Rango and myself.

OTV 3                                                    338 X 365 km
1 39025U 12071A   14221.09909657  .00000000  00000-0  00000-0 0    08
2 39025  43.5262 169.7938 0020000  74.4409 285.8674 15.73259206    06
Arc 20140808.8-0809.12 WRMS resid 0.044 totl 0.042 xtrk

I used Alberto's second point, both of Kevin's, and my single obs.

All elements were permitted to vary except eccentricity and rate of decay.

It may be of interest to note that the above elements do not come close to accounting for the 18.5 min early arrival
last night, relative the last observed orbit, five days earlier. Here is Mike McCant's TLE of early Aug 4 UTC:

                                                         337 X 369 km
1 39025U 12071A   14216.09424805  .00000000  00000-0  00000-0 0    09
2 39025  43.5382 200.4173 0023617  20.1551 339.1832 15.72764943    03

Here is my very similar version:

OTV 3                                                    340 X 366 km
1 39025U 12071A   14216.09424805  .00000000  00000-0  00000-0 0    09
2 39025  43.5256 200.3762 0019515  34.3091 325.1355 15.72763563    06
Arc 20140801.82-0804.11 WRMS resid 0.029 totl 0.013 xtrk

The difference in orbital period between last night's orbit and that of Aug 4 was ~1.73 s. Had the manoeuvre(s) to the
present orbit occurred immediately after the epoch of the Aug 4 TLE, then last night, after 79 revs, it would have been
~2.3 min. early. In all likelihood, the manoeuvre would have occurred later; therefore, this is the maximum difference
that would be expected.

Since the actual time of arrival was 18.5 min. early, the spacecraft must have made more than the apparent simple
manoeuvre(s) to slightly lower its orbit. It must have spent a significant fraction of the past five days at a
significantly different altitude than those of early Aug 4 or early Aug 9 UTC. The first step to possibly solving this
small mystery is to determine the present orbit to greater precision. In particular, the RAAN is moderately sensitive to
mean motion, much more so to inclination, so having a precise value will be key to possibly figuring out what happened,
or, more likely, bracketing the range of possible explanations.

Ted Molczan


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Received on Sat Aug 09 2014 - 10:10:13 UTC

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