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Cassini Update - March 3, 2006

Subject: Cassini Update - March 3, 2006
From:
Date: 3 Mar 2006 09:39:28 -0800
Newsgroups: sci.astro, alt.sci.planetary
Cassini Significant Events
for 02/23/06 - 03/01/06

The most recent spacecraft telemetry was acquired Wednesday, March 1,
from
the Goldstone tracking stations. The Cassini spacecraft is in an
excellent
state of health and is operating normally. Information on the present
position and speed of the Cassini spacecraft may be found on the
"Present
Position" web page located at
http://saturn.jpl.nasa.gov/operations/present-position.cfm .

Thursday, February 23 (DOY 054):

A very nice image of the big storm on Saturn is Astronomy Picture of
the Day
today.

Cassini Outreach and Saturn Observation Campaign members participated
in
Community Science Night at La Fetra Elementary School in Glendora,
California. Over 200 students, their families, and teachers attended.
In
addition to a school science fair, attendees all received Saturn and
the
moons of Saturn lithographs, and had access to excellent views of
Saturn and
other night sky objects through three telescopes.

Friday, February 24 (DOY 055):

Uplink Operations and the Spacecraft Operations Office sent commands to
the
spacecraft to mask, and then unmask the z-sigma ratio fault protection
monitor prior to the Titan 11 flyby. This strategy was first employed
for
the Titan 10 flyby on January 15, to prevent Titan appearing as an
unexpectedly bright body as it passed across the field of view of the
Stellar Reference Unit.

A non-targeted flyby of the satellite Helene occurred today.

Saturday, February 25 (DOY 056):

At periapse, Cassini came within 337,000 km of Saturn. On the inbound
leg,
the Composite Infrared Spectrometer (CIRS) performed limb sounding of
the
planet in the mid-infrared to obtain stratospheric thermal structure
with
especially good vertical resolution. The Radio and Plasma Wave Science
(RPWS) instrument looked for lightning whistlers and the fine temporal
structure of any Saturn electrostatic discharges that were detected.
After
periapse, the Visible and Infrared Mapping Spectrometer (VIMS) made a
thermal map of the night side of Saturn and then watched for lightning.
The
Ultraviolet Imaging Spectrometer (UVIS) observed with both extreme
ultraviolet (EUV) and far ultraviolet (FUV) during this observation.

Beginning Thursday, and running through today, Cassini Outreach
participated
in a national conference in Louisville, Kentucky, put on by the
National
After School Association.  The outreach team hosted a workshop on
'Reading,
Writing, and Rings' (RWR) to 30 attendees, and distributed RWR
information
and bookmarks at the NASA/JPL booth throughout the event.

Monday, February 27 (DOY 058):

The Titan 11 (T11) encounter was an outbound flyby of Titan with an
altitude
at closest approach of 1,813 km. The small solar phase angle approach
was
excellent for the Optical Remote Sensing (ORS) instruments. Activities
at
Titan began with a VIMS mapping of the Saturn-facing side of Titan
searching
for mid-latitude transient clouds and monitoring the surface for haze
and
photometric changes. Riding along, CIRS obtained information on trace
constituents in Titan's stratosphere, UVIS measured in both EUV and
FUV, and
the Imaging Science Subsystem (ISS) provided context imaging.

ISS followed with a global-scale mosaic of the hemisphere covering the
equatorial region from Fensal/Quivira/Aztlan to Aaru, and Tsegihi in
the
south.  Another mosaic ranged from the regional scale to high
resolution and
included the southern part of Aztlan, the eastern part of Shiwanni
Virgae,
and Elba Facula.  Since these observations covered regions where a
number of
Radar swaths terminate, they will be useful in the development of the
geodetic control network that is used to correlate co-ordinates on the
flat
image with their actual location on the spherical planetary body.

The focus then shifted to the Radio Science Subsystem (RSS). This was
the
first of four coordinated gravity field passes - the others occurring
in
T22, T33, and T38 - to determine the low degree coefficients of Titan's
gravity field. This knowledge may help to answer the question of
whether
Titan possesses an internal ocean. The four passes require disparate
geometries: two of these flybys must occur when Titan is near periapse
along
its orbit around Saturn and two flybys - of which T11 was one - must
occur
when Titan is close to its apoapse.  For each of these two pairs, one
flyby
must be on a nearly equatorial orbit with respect to Titan as was T11,
and
the other on an orbit with an inclination as large as possible.  Radio
Science also had two Gravity Science Enhancement (GSE) passes occurring
after the flyby.  The GSE passes are crucial to de-correlate Titan's
mass
from the distance at closest approach.

After the Radio Science experiment, UVIS made a slow scan across
Titan's
visible hemisphere to form spectral images. These observations in the
EUV-FUV wavelength will provide insight into atmospheric composition
and
structure. Following this, a CIRS far-infrared nadir composition map of
CH4,
HCN, and CO in Titan's stratosphere was performed. Trace constituents
in the
stratosphere may also have been detected.

For the Magnetospheric and Plasma Science instruments, T11 included an
equatorial wake passage differentiated from previous wake encounters by
being near Saturnian midnight, where a special dynamic plasma
environment is
expected. Cassini passed directly through the wake at an intermediate
altitude in comparison to T9, which was a distant wake passage.

Tuesday, February 28 (DOY 059):

The Cassini-Huygens Analysis and Results of the Mission (CHARM)
teleconference this week was a presentation by a Huygens Surface
Science
Package co-Investigator and dealt with the ongoing analysis and science
results from the probe data.

Radar carried out a radiometric calibration using the objects M17, Cass
A,
Taurus A and Orion as microwave sources for collection of radiometry
data.

Wednesday, March 1 (DOY 060):

Orbit trim maneuver (OTM) 53 was performed today. This is the cleanup
maneuver from the T11 encounter. The Reaction Control Subsystem burn
began
at 11:00 PM Pacific Time.  A "quick look" after a Reaction Wheel
Assembly
(RWA) bias following the maneuver showed the burn duration was 291.5
seconds, giving a delta-V of approximately 269.64 mm/s, including
everything
up through the RWA bias.  Upon returning to Earth-point after the
maneuver,
red alarms were received indicating that the helium latch valve driver
"A"
solid-state power switch had tripped. It was off at the time so there
was no
effect. All other subsystems reported nominal performance after the
event.

A delivery coordination meeting was held today for version 3.0 of the
Reaction Wheel Assembly Bias Optimization Tool (RBOT).  RBOT is
designed to
compute the bias, accomplish momentum management, and optimize
consumption
of resources for the reaction wheels.

Last week it was determined that Orbit Trim Maneuver 52 would be
cancelled.
Once that determination was made, it was possible to also cancel the
Cosmic
Dust Analyzer (CDA) decontamination mini-sequence scheduled for today.
The
CDA instrument team is concerned about contamination from the main
engine.
If we use the main engine, then a decontamination is performed,
otherwise
it's not.

Wrap up:

Check out the Cassini web site at http://saturn.jpl.nasa.gov for the
latest
press releases and images.


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