Cassini Significant Events
11/19/08 - 11/24/08
The most recent spacecraft telemetry was acquired on Nov. 24 from the Deep
Space Network tracking complex at Canberra, Australia. The Cassini
spacecraft is in an excellent state of health and all subsystems are
operating normally. Information on the present position and speed of
the Cassini spacecraft may be found on the "Present Position" page
at: http://saturn.jpl.nasa.gov/operations/present-position.cfm.
Wednesday, Nov. 19 (DOY 324):
An image of the unusual aurora over the north pole of Saturn is
Astronomy Picture of the Day today. It may be seen at:
http://antwrp.gsfc.nasa.gov/apod/ap081119.html.
Only sixteen days after its previous visit, Cassini once again
approached Titan for the mission's forty-eighth targeted encounter
with that satellite. Closest approach occurred on Wednesday, Nov. 19,
at 2008-324T09:17 Pacific Standard Time at an altitude of 1022.6
kilometers above the surface and a speed of 6.3 kilometers per
second. The latitude at closest approach was 21.6 degrees S.
TITAN-47 SCIENCE HIGHLIGHTS
For the first time in the Cassini mission, the Visual and Infrared
Mapping Spectrometer (VIMS) imaged the Huygens landing site at
closest approach with a resolution of better than one kilometer per
pixel. It covered areas that have already been observed with RADAR,
allowing for a joint study of geological features including dunes and
circular features that appear to be either impact craters or volcanic
calderas.
During stellar occultations before and after closest approach, VIMS
obtained information on atmospheric composition. The Ultraviolet
Imaging Spectrograph (UVIS) also observed two stellar occultations,
one each of Eta Ursa Majoris and Beta Canis Majoris. These gave
vertical profiles of hydrocarbons and aerosols in the high
stratosphere and mesosphere, a region that cannot be probed by other
instruments.
The Composite Infrared Spectrometer (CIRS) focused on limb sounding
of Titan at low latitudes. This observation was designed to measure
the spatial variations of trace gas species and isotopic ratios of C,
H, N and O, yielding insights into the formation and ongoing
evolution of the atmosphere.
The Ion and Neutral Mass Spectrometer (INMS) tried something new for
this flyby: riding along with VIMS to measure the dayside ionosphere
at low/equatorial southern latitudes. The instrument obtained a good
sampling of ions. INMS missed co-rotation, but saw the boundary when
Cassini brushed Titan's atmosphere. This is interesting for a
variety of reasons. This flyby is the first look at low equatorial
southern latitudes. It's also a relatively rare dayside pass.
Imaging Science (ISS) carried out global mapping and photometry of
the leading hemisphere, and rode-along with VIMS for global- and
regional-scale images. The areas included in the mapping were eastern
Xanadu, including Hotei Arcus, the Xanadu-Fensal/Aztlan boundary, and
western Tsegihi.
This was a rare Titan encounter for the Magnetospheric Imaging
Instrument (MIMI). Its Ion and Neutral Camera field of view remained
free of sunlight contamination throughout the pass. This was good for
seeing the energetic ion absorption both inbound and outbound. It was
also another opportunity for possibly encountering Titan outside the
magnetopause.
T47 was a first priority flyby for the Magnetometer Subsystem (MAG).
It was a flank-out flyby with a minimum altitude of 1023 km. The
geometry of this flyby made it complementary to T46 in the study of
the draping of the external magnetic field around Titan by covering
the dayside hemisphere. T47 took place in Saturn's near-noon sector
at 10.5 hours SLT, where Titan could be found in the magneto sheath
if the solar wind pressure was high.
Thursday, Nov. 20 (DOY 325):
The Spacecraft Operations Office (SCO) hosted a Project Review for
the fuel-side repressurization activity scheduled for execution in
January 2009. This is the last planned repressurization for the
Cassini propulsion system.
How many meetings can you pack in to a given day that require the
maximum number of people to attend? Here is a sample of a day in the
life of engineers and scientists that support sequence development
and the operation of a spacecraft. All these meetings were held
today, Nov. 20:
S45 Status & Scope - A weekly meeting that reviews all the activities
executed on board the spacecraft that week, and any problems or
issues that may have occurred.
S45 Command Approval Meeting for the DOY 329 Live Update
S46 Final Sequence Approval Meeting
S46 Command Approval Meeting for the S46 Background Sequence, Part 1
S46 Kick-off Meeting for the DOY 335-338 Live Update
SCO Project Review for the re-pressurization activity in January
SCO Status and Coordination Meeting
RBOT Process Improvement Meeting
Flight Software A8.7.7 Working Group
Orbit Determination Team Meeting
System Administrator bi-weekly team meeting
Friday, Nov. 21 (DOY 326):
The S48 Science Operations Plan process concluded today with the
transfer of all files and products to Uplink Operations. The kick-off
meeting for the Science and Sequence Update Process (SSUP) will be
held next Tuesday. S48 begins execution on-board the spacecraft on
Feb. 17. 2009.
Saturday, Nov. 22 (DOY 327):
Files for maneuver #173 due to execute on Sunday and a real-time
Radio and Plasma Wave Science (RPWS) whistler reaction wheel spin
down/spin up due to execute over the #173 backup pass on Monday were
both sent up to the spacecraft today.
Sunday, Nov. 23 (DOY 328):
Orbit Trim Maneuver (OTM) #173 was performed today. This was the
cleanup maneuver from the Titan 47 encounter on Nov. 18. The main
engine burn began at 2:45pm PST. Telemetry immediately after the
maneuver showed the burn duration was 4.66 seconds, giving a delta-V
of 0.77 m/sec. All subsystems reported nominal performance after the
maneuver.
Monday, Nov. 24 (DOY 329):
Non-targeted flybys of Helene and Tethys occurred today.
Continuing the Magnetospheric and Plasma Science (MAPS) study of
Saturn's auroral regions, the Cassini Plasma Spectrometer (CAPS)
started off the day's science by controlling the spacecraft attitude
for all of the MAPS instruments. CIRS followed this activity with the
first of two observations on this day carefully designed to study how
ring temperatures vary from the lit side to the unlit side of the
rings. Approaching the rings from above Saturn's north pole, CIRS
scanned the rings' unlit side. This was followed by two ISS
observations: one to observe Helene during the mission's
second-closest flyby of this body, the other to study Saturn's moon
Tethys. The CIRS scans of the lit side of the rings that were taken
afterwards were meant to be compared with the scans of the unlit side
of the rings taken earlier in the day. As Cassini passed through the
ring plane, both the Cosmic Dust Analyzer (CDA) and RPWS measured the
amount of dust the spacecraft encountered.
Science Planning (SP) has performed an analysis on the post OTM-173
orbit determination solution provided for the DOY 335-339 Live
Inertial Vector Propagator (IVP) update. The S46 sequence leads have
been informed that an update will probably be required. ISS and CIRS
have concurred. The update is now being generated with SCO.
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