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Cassini Significant Events for 08/24/06 - 08/30/06



Cassini Significant Events
for 08/24/06 - 08/30/06

The most recent spacecraft telemetry was acquired Wednesday, August 30, 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, August 24 (DOY 236):

A delivery coordination meeting was held today for the Spacecraft Operations
Office (SCO) Downlink Uplink Coherency Tool (DUCT) version 1.1. This is the
tool that automates the insertion of a downlink pause in the sequence at the
point of the transition from one-way to two-way where otherwise a brief
telemetry loss would occur.

The Encounter Strategy Meeting for Titan 17 and Titan 18 was held today.
The time frame addressed was from September 7 through September 23 and
included Orbit Trim Maneuvers (OTM) 71 through 73.  Presentations included a
mission overview covering special mission activities, first time events,
consumables, live updates potentially needed for this period, a sequence
overview and contingency planning for S23, and presentations by SCO,
Navigation, and Uplink Operations.

The deputy Project Scientist gave a presentation on Saturn's rings in Von
Karman Auditorium today.  The presentation included how the rings are made
up of millions of icy particles ranging in size from dust to large boulders,
and how these particles undergo an intricate dance as they orbit Saturn.
Also covered was how gravity from the nearby moons causes the ring particles
to bump into each other and create interesting patterns in the rings such as
waves and wakes. The talk was given as part of the Science Division's
monthly "Science 101" lecture series.

The S26 official port occurred today as part of the Science Operations Plan
Update process.  The input products have been sent to AACS for analysis with
the results to be delivered this week.  The S26 project briefing is
scheduled for September 6.

Friday, August 25 (DOY 237):

The Optical Remote Sensing Instruments were quite busy this week.
Observations included the occultation of the star 8 Nu Cap by Tethys by the
Ultraviolet Imaging Spectrograph (UVIS), along with calibrations performed
by observing the ring occultations of Zeta Opiuchus, Delta Sco, and Lambda
Sco. The Cassini Infrared Spectrometer (CIRS) ran a scattered light test to
quantify the effect of ring particle impacts on the performance of its
mirrors. The Imaging Science Subsystem (ISS) took a standard star image to
monitor instrument sensitivity, three pictures of Saturn's satellites were
taken for the Optical Navigation team to assist with orbit determination,
and a 13.5 hour lightning search of Saturn's northern hemisphere was
performed.  Finally, the Visual and Infrared Mapping Spectrometer (VIMS)
performed a mosaic of the entire ring system near apoapsis, Cassini's
farthest point from Saturn during the 27th orbit. The suite of
Magnetospheric and Plasma Science (MAPS) instruments continued its
magnetotail campaign by observing the structure and dynamics of Saturn's
magnetotail at low latitudes.

Saturday, August 26 (DOY 238):

An AACS Reaction Wheel Assembly (RWA) friction test was performed today on
wheels 1, 2, and 4.  In this test, performed every three months, the RWAs
are spun to +/-900 rpm and allowed to run down to zero.  The longer the
run-down time, the better.  RWA-1 exhibited no change in the counter
clockwise direction since the last test on May 29, 2006, but was poorer in
the clockwise direction.  The rundown time was 20 minutes, equaling the
previous low point in the fall of 2004.  This lower result was caused by the
presence of drag torque spikes throughout the clockwise part of the friction
test.  RWA-2 exhibited no change in either direction, with both directions
having rundown times of greater than 40 minutes.  RWA-4 showed no change in
the counter clockwise direction, but was slightly worse in the clockwise
direction, with a run-down time of 38 minutes.

Monday, August 28 (DOY 240):

The Aftermarket Process for the S28 sequence began today.  This 5-week
process addresses proposed changes that require re-integration of the
segments contained in the S28 sequence.  All proposed science and
engineering changes were submitted via the Cassini Information Management
System by last Friday, August 24, 2006.  A final decision meeting is
scheduled for September 11.

The Cassini-Huygens Analysis and Results of the Mission (CHARM)
teleconference for August was held today. The topic:  Exploring Saturn's
Moon Titan, An Earth-like Alien.  The presentation covered what is known and
what the possibilities are for Titan's atmosphere and geology, what is known
from the Huygens Probe, and specific data acquired from some of the Cassini
instruments,

Wednesday, August 30 (DOY 242):

The Navigation Team announced that OTM-070 could not be cancelled and would
execute as planned on Monday, September 4.  Currently OTM-070 has a
predicted value of 0.227 m/s. Cancellation would increase the mission
delta-V by about 15 m/s.  The preliminary and final cancellation reviews
scheduled for Thursday and Friday have been, well, cancelled.  OTM 70
removes the pointing errors at Titan, but the Enceladus post-Titan pointing
errors remain large.  Final trajectories will be provided Friday for science
evaluation.

The Radio Science Subsystem (RSS) performed a High Gain Antenna boresight
calibration near the middle of today's downlink to the Goldstone 70M
antenna.  An hour of this activity required a cross-hair maneuver that took
Cassini slightly off Earth-point.  As a result, a brief, planned
interruption to the downlink occurred.

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 Spsce 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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