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Cassini Significant Events for 12/19/07 - 12/25/07

Cassini Significant Events 
for 12/19/07 - 12/25/07

The most recent spacecraft telemetry was acquired on Tuesday, December 25,
from the Goldstone tracking complex. 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" web page located at

Wednesday, December 19 (DOY 353):

The Cassini Radio Science (RSS) orbit 54 Saturn rings and atmospheric
occultation observation was completed successfully today. The experiment was
covered by Madrid's DSS-63 for S- and X-band support, and DSS-55 for X- and
Ka-band support. Observations included the first chord ring occultation with
inbound and outbound occultations on the same ring side, as well as ingress
and egress ionospheric and atmospheric Saturn occultations.

The ring-opening angle of 6.6 degrees occurring at this time is the smallest
so far in the prime mission.  With the angle this small, the occultation
will provide excellent sensitivity to ring structure of relatively small
optical depth. The atmospheric occultations probe southern Saturn latitudes
of about 16 and 68 degrees on the ingress and egress sides, respectively.
The two are part of a campaign of occultations during the last year of the
prime mission that probe low, mid, and high southern latitudes of Saturn,
complementing several near-equatorial occultations earlier in the mission.

After the RSS observations were complete, the spacecraft transitioned from
reaction wheel to thruster control for the duration of a Radio and Plasma
Wave Science (RPWS) Whistler observation.

Thursday, December 20 (DOY 354):

On Dec. 20, Cassini flew by Titan at an altitude of 970 km and a speed of
6.3 km/sec for the T39 targeted encounter.  This was the last Titan flyby
under 1000 km in the prime mission.  Scientific observations for T39
included RADAR obtaining high resolution Synthetic Aperture RADAR (SAR)
coverage of the south-pole region at closest approach, and reaching to
around 70 degrees. The Composite Infrared Spectrometer (CIRS) measured
stratospheric temperatures as well as obtained limb measurements and
vertical temperature and compositional profiles. Imaging Science (ISS)
collected a full disk color sequence at 1.4 km/pixel, and performed low
phase angle measurements of Rhea.  Finally, the Visual and Infrared Mapping
Spectrometer (VIMS) mapped the mid-latitude regions at small solar phase
angles, monitored cloud motions on a global scale, and monitored the probe
landing site. For more details on this flyby, link to:

Friday, December 21 (DOY 355):

Thanks to an accurate delivery to the Titan 39 flyby, Orbit Trim Maneuver
(OTM) #140, due to execute on December 23, has been determined to have a
magnitude of 0.4 mm/s, and delta V cost of cancellation of only 1.1 mm/sec.
Based on this, the decision has been made to cancel OTM 140.

After today, the flight team will begin the annual two-week break from
sequence development.  The decision was made early on in the mission to
pause development at this time due to the number of individuals taking time
off for the holidays, and the differences in holiday schedules between the
US and Europe.  Work will begin again on S37-S41 on Jan. 7.

Monday, December 24 (DOY 358)

An image taken from edge-on with the ring plane, and containing four of
Saturn's attendant moons, Tethys, Enceladus, Hyperion and Epimetheus, is
available for viewing at:

Today marks the 3rd anniversary of the release of the Huygens Probe to begin
the journey to Titan on Christmas Eve, 2004. 

Wrap up:

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

The Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a
division of the California Institute of Technology in Pasadena, manages the
Cassini-Huygens mission for NASA's Science Mission Directorate, Washington,
D.C.  JPL designed, developed and assembled the Cassini orbiter.

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