WGS 4: 2nd stage fuel dump imaged by Willie Koorts

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Sat Jan 21 2012 - 04:15:31 UTC


Last night, Willie Koorts successfully imaged the cloud that resulted from the fuel dump by WGS 4's 2nd stage rocket. He
observed from the SAAO's Sutherland site, east of Cape Town, South Africa.

WGS 4 was launched from Cape Canaveral on a Delta IV rocket, on 2012 Jan 20, at 00:38 UTC. At 01:09:36 UTC, the second
stage inserted itself and its payload into approximately the following highly elliptical orbit:

                                                       440 X 66991 km
1 78901U          12020.04833334  .00000000  00000-0  00000-0 0    01
2 78901  24.0048 310.2300 8299446 177.8402   1.4113  1.08160032    06

The payload separated about 10 min later. The following map shows the ground track and point of final orbit insertion
(4) and spacecraft separation (5): http://www.spaceflightnow.com/delta/d358/track.html

By 01:25:20 UTC, the 2nd stage had completed its Collision and Contamination Avoidance Manoeuvre, and gradually
separated from its payload. Soon after, it began to dump excess hydrogen, oxygen and hydrazine. The rapidly expanding
gas plume was illuminated by the sun, creating a brilliant cloud, readily to visible to anyone with a good view of the
orbit.

Willie knew that his view would be far from ideal, due to the predicted ultra-low elevation of the 2nd stage above the
horizon at the time of fuel dump, and its close proximity to the crescent moon (mag -7.7). He maximized his probability
of success by heading out to the SAAO's Sutherland site, which is high atop a plateau, affording a clear view nearly to
the horizon. As he approached the site, he saw that he would face an additional challenge: clouds had begun to encroach
upon the otherwise clear sky, and they were right in the vicinity of the expected fuel dump.

Despite the challenges, Willie obtained good images of the dump, as shown in the following sequence of photos. The
filenames denote the approximate UTC time. The cloud was small and barely visible through the clouds in the first image
(at the URL below). Elevation was just 8.1 deg, and the range to the cloud was about 11,500 km. Its celestial location
was in Ophiuchus, but the most prominent stars in the photo are in Scorpius, visible near the upper right.

http://satobs.org/seesat_ref/misc/01h35.48.jpg

Eight minutes later, the object had descended to 5.4 deg elevation, and its range was 14,300 km:

http://satobs.org/seesat_ref/misc/01h44.08.jpg

Four minutes later, elevation was 4.4 deg, and range was 15,600 km. Despite the increasing distance, the angular size
was growing, and its complex shape was readily apparent:

http://satobs.org/seesat_ref/misc/01h48.07.jpg

Nearly two minutes later, elevation was 4.1 deg and range was 16,200 km:

http://satobs.org/seesat_ref/misc/01h49.56.jpg

A couple minutes later, elevation was 3.7 deg and range was 16,700 km. It was fairly large - at least 1 deg in diameter,
judging by the bright star pair at far left (delta and epsilon Opiuchi), which are about 1.4 deg apart. At 16,700 km
radius, 1 deg is about 290 km.

http://satobs.org/seesat_ref/misc/01h51.38.jpg

Some seven minutes later, the object was just 2.6 deg above the horizon and 18,800 km distant (at altitude 13,700 km):

http://satobs.org/seesat_ref/misc/01h58.50.jpg

Willie's home page has a nice photo of the observing site, and information on his many astronomy-related interests:

http://wpk.saao.ac.za/

Thank you, Willie for getting up in the middle of the night to make these observations and for sharing them with us.
Thank you also to Mike McCants who noticed the opportunity and alerted Greg Roberts, who alerted Willie to the
opportunity. Greg also stayed up for the event in the faint hope that his overcast sky would clear; alas it did not.

Ted Molczan


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