NROL-35 Centaur de-orbit/fuel dump

From: C. Bassa via Seesat-l <seesat-l_at_satobs.org>
Date: Tue, 30 Dec 2014 18:48:50 +0100
The fuel dump of the recent NROL-35 launch was widely observed from
Europe. The best documented observations were obtained by William
Stewart (http://www.britastro.org/node/5886) from the UK. He obtained
a set of 1s exposures at 6400ISO with a 300mm F/5.6 lens on a Canon
EOS 550D with timestamps accurate to 1 second. His images span the
time between 05:09UT to 05:19UT on December 13th and show what the
analysis below identifies as the exhaust of the de-orbit burn and the
subsequent fuel dump from the Centaur upper stage.

William kindly shared his images and I used my software to calibrate
the astrometry of 57 images. Though the payload and Centaur are not
visible on the images, the fuel dump allows the position of the
Centaur to be estimated, yielding the 51 positional measurements
below. A further 8 positions were measured from the apex of the fan
shaped cloud belonging to the exhaust of the de-orbit burn.

From the astrometrically calibrated images, I created the following
two image sequences. The first sequence has all images projected onto
the sky such that the stars remain fixed, showing the motion of the
exhaust and the dumped fuel with respect to the stars. The second
sequence uses the orbit of USA 259, the NROL-35 payload, that Ted
Molczan determined from observations by Peter Wakelin and Scott Tilley
(http://www.satobs.org/seesat/Dec-2014/0096.html), to center each
image to the predicted location of USA 259. This shows the exhaust and
fuel dump relative to the location of the payload USA 259. I have also
converted this image sequence into a video showing the progression
with time. The timestamps are in UT on 2014-12-13, and the field of
view is 2.78x2.78 degrees.

Image sequence centered on stars: https://db.tt/UEG09P6c
Image sequence centered on payload: https://db.tt/q56CMzJp
Video centered on payload: https://db.tt/iZHzGJJJ

The image sequence centered on the payload shows that the fan shaped
cloud remains relatively stationary to the payload and points away
from the Centaur. Furthermore, the Centaur is moving away from the
cloud, which confirms that the fan shaped cloud is the exhaust of the
de-orbit burn. The fuel dump then becomes visible between 05:11:05 and
05:11:13 and continually grows until the end of the image sequence.

Extrapolating the movement of the fuel dump on the sky back to the
exhaust suggests the de-orbit burn occured between 05:06:22UT and
05:08:07UT. As the USA 259 orbit puts it at a distance of 19300km from
the observer, the observed angular rate of 2.67 to 4.34"/s limits the
velocity difference of the Centaur with respect to the payload to 0.25
to 0.41 km/s. As there is likely also a line-of-sight component to the
velocity, the real delta-v imparted by the de-orbit burn is likely
somewhat larger.

To obtain a better estimate of the de-orbit burn the following
procedure was used. First, the USA 259 orbit was fitted against the
exhaust measurements, allowing for changes in mean anomaly, RA of
ascending node, and argument of perigee. This yielded the following
orbit below.  Evaluating the orbit to 05:07:15UT, the middle of the
de-orbit burn time range, gives the XYZ position at the time of the
burn. Secondly, the Centaur de-orbit NOTAM sets the de-orbit area
centered around 138.6E, 48.3S. The NOTAM was valid from 13:02 to
14:08UTC. Selecting the center of this time range gives an estimate of
the deorbit XYZ position. Finally, I fit the measurements of the
fuel dump together with the XYZ positions for the de-orbit burn and
de-orbit to estimate the orbit of the Centaur after the burn. This
shows that the de-orbit burn imparted a delta-v of 0.512 km/s.

Exhaust apex
1 99999U 14847B   14348.24158565  .00000000  00000-0  00000-0 0    08
2 99999  62.8507 212.5258 6776416 267.5168  68.3677  2.03510246    02
# 20141213.22-20141213.22, 8 measurements, 0.007 deg rms
Post-burn Centaur orbit
1 99999U 14847A   14347.21336806  .00000000  00000-0  00000-0 0    00
2 99999  63.9343 213.3019 7301375 253.5845  40.8155  2.47023627    08
# 20141213.22-20141213.22, 51 measurements, 0.032 deg rms

The following observations use a dummy site ID of 9990, which
corresponds to 53.0574N, 2.5688W, 65m in elevation.

Exhaust apex measurements
99999 14 847B   9990 G 20141213050947473 27 25 1546209+102847 17 S
99999 14 847B   9990 G 20141213050954471 27 25 1546345+103379 17 S
99999 14 847B   9990 G 20141213051002506 27 25 1546485+103901 17 S
99999 14 847B   9990 G 20141213051039486 27 25 1547141+110428 17 S
99999 14 847B   9990 G 20141213051045534 27 25 1547203+110778 17 S
99999 14 847B   9990 G 20141213051105492 27 25 1547575+112112 17 S
99999 14 847B   9990 G 20141213051113527 27 25 1547717+112616 17 S
99999 14 847B   9990 G 20141213051123463 27 25 1547880+113222 17 S

Centaur measurements of fuel dump
99999 14 847A   9990 G 20141213051113527 27 25 1546781+111334 17 S
99999 14 847A   9990 G 20141213051123463 27 25 1546925+111889 17 S
99999 14 847A   9990 G 20141213051138497 27 25 1547139+112792 17 S
99999 14 847A   9990 G 20141213051147482 27 25 1547257+113325 17 S
99999 14 847A   9990 G 20141213051154481 27 25 1547345+113681 17 S
99999 14 847A   9990 G 20141213051200529 27 25 1547431+114064 17 S
99999 14 847A   9990 G 20141213051207527 27 25 1547524+114481 17 S
99999 14 847A   9990 G 20141213051213489 27 25 1547605+114826 17 S
99999 14 847A   9990 G 20141213051219537 27 25 1547679+115163 17 S
99999 14 847A   9990 G 20141213051224462 27 25 1547762+115438 17 S
99999 14 847A   9990 G 20141213051231460 27 25 1547859+115855 17 S
99999 14 847A   9990 G 20141213051239495 27 25 1547964+120319 17 S
99999 14 847A   9990 G 20141213051322522 27 25 1548385+122675 17 S
99999 14 847A   9990 G 20141213051330471 27 25 1548459+123113 17 S
99999 14 847A   9990 G 20141213051551476 27 25 1550157+134835 17 S
99999 14 847A   9990 G 20141213051558474 27 25 1550223+135227 17 S
99999 14 847A   9990 G 20141213051605473 27 25 1550327+135614 17 S
99999 14 847A   9990 G 20141213051612471 27 25 1550417+140002 17 S
99999 14 847A   9990 G 20141213051619470 27 25 1550499+140370 17 S
99999 14 847A   9990 G 20141213051625518 27 25 1550577+140701 17 S
99999 14 847A   9990 G 20141213051631479 27 25 1550640+140961 17 S
99999 14 847A   9990 G 20141213051635540 27 25 1550678+141226 17 S
99999 14 847A   9990 G 20141213051640465 27 25 1550743+141452 17 S
99999 14 847A   9990 G 20141213051646513 27 25 1550823+141774 17 S
99999 14 847A   9990 G 20141213051652474 27 25 1550879+142123 17 S
99999 14 847A   9990 G 20141213051657486 27 25 1550958+142423 17 S
99999 14 847A   9990 G 20141213051704484 27 25 1551030+142697 17 S
99999 14 847A   9990 G 20141213051710532 27 25 1551094+143059 17 S
99999 14 847A   9990 G 20141213051715543 27 25 1551161+143324 17 S
99999 14 847A   9990 G 20141213051720468 27 25 1551229+143605 17 S
99999 14 847A   9990 G 20141213051725479 27 25 1551289+143822 17 S
99999 14 847A   9990 G 20141213051730490 27 25 1551353+144101 17 S
99999 14 847A   9990 G 20141213051734465 27 25 1551413+144375 17 S
99999 14 847A   9990 G 20141213051739476 27 25 1551468+144607 17 S
99999 14 847A   9990 G 20141213051744487 27 25 1551525+144849 17 S
99999 14 847A   9990 G 20141213051748462 27 25 1551583+145070 17 S
99999 14 847A   9990 G 20141213051752522 27 25 1551639+145297 17 S
99999 14 847A   9990 G 20141213051758484 27 25 1551716+145598 17 S
99999 14 847A   9990 G 20141213051805482 27 25 1551783+145975 17 S
99999 14 847A   9990 G 20141213051815505 27 25 1551906+150460 17 S
99999 14 847A   9990 G 20141213051819479 27 25 1551967+150726 17 S
99999 14 847A   9990 G 20141213051824490 27 25 1552032+150966 17 S
99999 14 847A   9990 G 20141213051830538 27 25 1552080+151282 17 S
99999 14 847A   9990 G 20141213051835463 27 25 1552155+151548 17 S
99999 14 847A   9990 G 20141213051840474 27 25 1552208+151786 17 S
99999 14 847A   9990 G 20141213051845486 27 25 1552278+152043 17 S
99999 14 847A   9990 G 20141213051849460 27 25 1552324+152303 17 S
99999 14 847A   9990 G 20141213051854471 27 25 1552389+152520 17 S
99999 14 847A   9990 G 20141213051859482 27 25 1552443+152790 17 S
99999 14 847A   9990 G 20141213051904494 27 25 1552527+153042 17 S
99999 14 847A   9990 G 20141213051910542 27 25 1552607+153406 17 S

Regards,
   Cees
_______________________________________________
Seesat-l mailing list
http://mailman.satobs.org/mailman/listinfo/seesat-l
Received on Tue Dec 30 2014 - 17:48:50 UTC

This archive was generated by hypermail 2.3.0 : Tue Dec 30 2014 - 17:49:45 UTC