Cassini Significant Events -- 04/13/06 - 04/19/06

April 21, 2006

(Source: Cassini Project)

The most recent spacecraft telemetry was acquired Wednesday, April 19, 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 .

Thursday, April 13 (DOY 103)

A successful end-to-end test was held in the Integrated Test Laboratory
(ITL) for a CDS Command Loss Timer (CLT) patch to be uplinked to the
spacecraft beginning May 8. The patch corrects a code error discovered last
September when the CLT was set to a different value for OTM-31, which caused
a data loss for the Titan-7 flyby. A temporary patch to restore normal
operations was uplinked at that time. This patch is a permanent fix to the
code. The uplink readiness review for this delivery will be held on April
17, followed by a Software Requirements and Certification Review on April

As was reported last week, the final step in the Monopropellant Tank
Assembly (MTA) recharge and flight software patch procedure was to be a
reaction wheel assembly (RWA) bias. This bias, the first use of thrusters
after the MTA recharge, executed successfully and provided an opportunity to
perform an in-flight calibration of the higher thrust levels. There were no
red alarms, no rejected commands, and no unexpected fault protection (FP)
activity. The attitude error was small and well below the FP threshold.

Friday, April 14 (DOY 104)

After input was received from Science Planning and participating science
teams, it was determined that the DOY 115 Live Inertial Vector Propagator
update could be cancelled. Analysis showed that the highest error is 0.38
mrad for Janus, with most of the errors below 0.1 mrad.

A team from JPL Media Relations filmed two classrooms in the Bay Area. These
two classrooms were working through the "Reading, Writing, and Rings"
lessons. The footage collected from this filming will be edited with
interviews of the content developers. The final products will serve two
purposes: to expose audiences to the curriculum as well as to train
educators in the pedagogy of the lessons.

The outreach team submitted the following information on Saturn viewing.
Whether you live in the city or the country, you can view Saturn and Mars
this month. Just look to the west in the evening, about halfway between
horizon and overhead. Both planets can be spotted near the Gemini
Constellation in the western sky. Here's where to look:

Monday, April 17 (DOY 107):

Final sequence approval and command approval meetings were held for the S20
background sequence and related files. During the evening pass over
Goldstone, all seven instrument expanded block files were uplinked to the
spacecraft. Part one of the background sequence will go up to the
spacecraft on Wednesday.

An ITL run for Orbit Trim Maneuver (OTM) #58, originally planned for April
17 and 18, was cancelled. The test was to verify the first-time event of
powering on the accelerometer over an RCS burn in order to calibrate the
thrusters following the MTA recharge performed last week. It turns out
OTM-58 will be too small. ACS wants an RCS burn with a delta-V of at least
0.1 m/sec. The Spacecraft Operations Office will try again with OTM-59,
which is currently estimated at about 0.3 m/sec.

The S22 Science Operations Plan Update official input port occurred today.
The merged products are currently being run through the end-to-end pointing
validation process by ACS. The Project Briefing and Waiver Disposition
Meeting is scheduled for Wednesday, April 26. The SOP Update product is
handed off to uplink operations on Friday, April 28.

Tuesday, April 18 (DOY 108):

For S21, the leads are planning to schedule an ITL test to ensure that
de-registration of S20 part 2, and the registration of the S21 background
sequence occur as expected. S21 will be the first time a sequence is
uplinked following a split sequence. The simulation coordination meeting
will occur on April 21.

Science activities this week included the continuation of the Cosmic Dust
Analyzer search for Saturnian dust stream particles, Composite Infrared
Spectrometer high spectral resolution composition observations of Saturn -
this time they will be observing at 60N latitude - and Ion and Neutral Mass
Spectrometer scans for dense particle regions far from Saturn. The Imaging
Science Subsystem has wrapped up its icy satellite high phase
spectrophotometry campaign.

Wednesday, April 19 (DOY 109):

The fourth science archive delivery, scheduled for April 1, has gone very
well with most instrument teams delivering earlier than the scheduled due
date. The next science archive delivery is scheduled for July 1.
A member of the Visual and Infrared Mapping Spectrometer (VIMS) instrument
team gave a talk today to the flight team on "Saturn and Titan Revealed: New
Infrared Views of Hidden Clouds, Dynamics, and Chemistry from Cassini/VIMS"
Part 1 of the S20 background sequence was sent to the spacecraft today at
109T22:06:00. The sequence's registration and activation have been
confirmed. Part two will go up on May 11 and begin execution on May 13.

Extended Mission Report: Science Planning and the instrument teams are
working on defining a set of evaluation metrics for use in selection of an
extended mission tour. Some of the metrics suggested include the total
number of Titan flybys, number of Titan flybys per year, delta-V left over
at end of a 2-year tour, delta-V per flyby, plot of the distribution of
closest approach latitudes/longitudes, solar occultation latitude
distribution, Radio Science occultation latitude distribution, plots of
ground tracks with altitude, plots of ground tracks with phase, overlap
between surface images, plot of phase vs. altitude, mid-tail region, Titan
tail passages, and number of Titan flybys while Titan is in Saturn's shadow.
As you can see from this partial list, balancing science priorities and
selecting a tour is not an easy task.

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