Cassini Significant Events
for 12/23/08 - 01/06/09

The most recent spacecraft telemetry was acquired on Jan. 6 from the
Deep Space Network tracking complex at Goldstone, California.  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/mission/presentposition/

Tuesday, Dec. 23 (DOY 358):

Activities on the ground have been minimal over the last two weeks
due to the holiday period.  An interesting twist was the possibility
of an unplanned live update as the result of the cancellation of
Orbit Trim Maneuver (OTM) 179. Read on for details.

The propellant cost for cancellation of OTM-179 -- due to execute
tomorrow, Christmas Eve - was only about 0.46 m/s.  Execution would
have required the insertion of a bias prior to the OTM in order to
eliminate a period of about one hour of low rpm time on one of the
reaction wheels. Because of the low cost and the complications
associated with the RWA bias, and in order to give the flight team a
break and reduce work over the holiday, OTM-179 was cancelled.

Remember that every time Cassini performs a maneuver, the result is
an adjustment to the spacecraft trajectory to keep it flying along
the route planned for it by the Navigation team.  Canceling a
maneuver means the trajectory will be slightly different from what
was planned.  For many prior cancellations, the change in spacecraft
pointing as a result of the change in the trajectory was so minimal
that there was no impact.  In this case, the impact to science
pointing was not clear. At the weekly Operations Status and
Coordination meeting, Science Planning announced that an unplanned
live update might be necessary. Based on the latest orbit
determination solution, pointing was a bit off for an Imaging Science
(ISS) observation of Tethys due to execute on Jan. 4. With tomorrow
being Christmas Eve, a schedule was set by the sequence leads for a
Go/No Go meeting on Monday, Dec. 29, and uplink of the files just
prior to execution.  Science would have to perform their analysis
quickly in order to meet the schedule.  As it turned out, the input
from Science was that this was a high phase Tethys observation at
~500,000 kilometers.  It was not high enough priority to recommend
unplanned work over the holidays for the uplink people.  The update
became a No/Go.

A traveling exhibit called Spectacular Saturn - Images from the
Cassini-Huygens Mission ended a three-month run at the Herbert F.
Johnson Museum of Art at Cornell University this week.  Over 35,000
visitors attended the exhibit, which will now transfer to the
National Air and Space Museum in Washington where it is due to open
on February 2.

Saturn is now visible in the eastern evening sky by mid evening.
Telescope viewers are in for a real treat in 2009.  Since 1995 we
have been seeing the southern face of the rings.  Saturns rings start
2009 nearly edge-on; open slightly showing the south side of the
rings through May, tipping back to an edge-on view in September, a
view that wont be seen again for approximately 14.5 years. After
Saturn passes conjunction with the Sun in late September, Saturns
north side of the rings is visible and open slightly through the rest
of the year, but youll have to get up before dawn to see them!

Part two of the S46 background sequence, which was uplinked to the
spacecraft back on Dec. 12, began execution today.  Part two will run
until Jan. 9 when S47 takes over.

Wednesday, Dec. 24 (DOY 359):

An update to the ISS planning software Imaging Science Subsystem
Pre-commanding Tool was installed for operational use last week.
ISSPT is used by the Support Imaging team to set the image parameters
for support images.

 From now through the next 5 days, the spacecraft is the one that did
all the work! Here is what went on:

Dec. 24, DOY 359:
Ultraviolet Imaging Spectrograph (UVIS): Observed stellar ring
occultations of the stars Delta Centauri and Beta Crucis
Cassini Plasma Spectrometer (CAPS): Pointed the spacecraft for the
Magnetospheric and Plasma Science (MAPS) survey of the magnetosphere
ISS: Observed several small satellites as part of a satellite orbit
campaign

Dec. 25, DOY 360:
Composite Infrared Spectrometer (CIRS): Mapped the thermal emission
of the rings at 60 degrees north latitude and mid-phase
Optical Remote Sensing (ORS) instruments: With UVIS as prime,
observed the occultation of Alpha Arae by the rings.
ISS: targeted the rings to produce short movies of selected features.
CIRS: Scanned the rings at 20 degree north latitude and high phase as
one of multiple observations designed to look at both the lit and
unlit sides of the rings at similar geometries to study the vertical
thermal distribution within the rings.

Dec. 26, DOY 361:
ISS: Targeted the icy moon Enceladus to obtain medium resolution
images of the plumes at high phase.
CIRS: Scanned the rings at 20 degrees south latitude at high phase to
study the vertical thermal distribution.
Visual and Infrared Mapping Spectrometer (VIMS): Performed a high
phase rings composition observation with CIRS and UVIS as riders
CIRS: Followed with a scan of the Encke Gap within the A ring.

Dec. 27, DOY 362:
CIRS: The day was filled with a 21 hour CIRS rings observation that
continued into DOY 363.  This was an excellent opportunity for
obtaining thermal azimuthal scans at several radii in each of the
major - A, B, and C - ring systems.  The instrument looked for
variations in the temperatures as a function of local hour angle with
emphasis on the rings particles as they entered the shadow of Saturn.
 From this information, scientists learn about how quickly the ring
particles cool down and heat up, which in turn tells them about the
structural properties of the ring particles.

Dec. 28, DOY 363:
ORS: With ISS as prime, obtained one more of hundreds of distant
observations of Titan designed to improve understanding of the clouds
on Titan.
Magnetometer (MAG): Performed a rolling calibration, which is done
outside of 15 Rs.

Dec. 29, DOY 364:
CIRS: Performed regional mapping of Saturns upper troposphere in the
far infrared. These are repeated over the course of the mission to
reveal seasonal variations.


Monday, Dec. 29 (DOY 364)

Back to work!

With S47 beginning execution on Jan. 9, the process has now begun for
assessment of the first live update for that sequence, scheduled to
execute Jan. 12-14.  Saturn and Rhea are the targets, with
observations planned by ISS, CIRS, and VIMS.  Science Planning has
deferred the Go/No go decision to the instrument teams.  The kick off
meeting is scheduled for Jan. 5 with the Go/No go on the 6th.

Tuesday, Dec. 30 (DOY 365):

The Command Loss Timer setting was increased in the background
sequence to 5 days on Dec. 30 for the time range Dec. 31, 2008 to
Jan. 4, 2009. It will be restored to 90 hours on January 4, 2009.
The command loss timer is part of system fault protection on board
the spacecraft.  If the craft does not hear from the ground within a
specified period of time between commands, it automatically takes
steps to protect itself. Since the Cassini Program had scheduled DSN
tracks approximately every other day from Dec. 29 through Sunday,
Jan. 4, it made sense to increase the CLT duration for this period.

More science:

Dec. 30, DOY 365:
CIRS: With UVIS riding along, stared at Saturn for over twelve hours
to measure oxygen compounds in the stratosphere. Each such study
focuses on aparticular latitude. Today the sub-spacecraft latitude
was 14 degrees.
UVIS: Made several slow scans across Saturns visible hemisphere to
form spectral images in both the far ultra-violet and the extreme
ultra-violet.

Dec. 31, DOY 366:
ORS: Performed a long range, low phase observation of Dione.
VIMS: Performed an in-flight calibration of the solar port.

Jan. 1, DOY 001:
MAPS: Took over pointing control of the spacecraft to direct activity
to monitoring the plasma and field characteristics. CIRS:  As Cassini
headed back toward Saturn, the distance from the planet was again
appropriate for regional mapping by CIRS of the upper troposphere in
the far infrared. Repeating these observations provides measurements
that can be compared for temporal variations. VIMS: Observed the
Pleiades to provide in-flight characterization of the pixel look
directions within the instrument. This supports geometric calibration
 of images.

Jan. 2, DOY 002:
VIMS: Began the first of several lengthy studies of the polar regions
to study the structure and dynamics of the polar vortices and their
variability over time, including seasonal changes.

Jan. 3, DOY 003:
UVIS:  An occultation of Beta Cru by Saturn provided an opportunity
for UVIS to measure the vertical profile of aerosol and gas opacity
as well as temperature at the highest altitudes of Saturns atmosphere.
VIMS:  With ISS and UVIS participation, returned to the polar dynamics
study.
The north polar region is experiencing sunlight for the first time
since Cassini has been at Saturn. Images of the north pole from VIMS,
as well as ISS and UVIS, will reveal the structure and microphysical
nature of upper tropospheric clouds that help form the bizarre
hexagonal feature there.

Jan. 4, DOY 004:
Several Cassini remote sensing instruments - in particular ISS, UVIS,
and VIMS made a collective, concerted effort to reveal the
multifaceted nature of polar aurorae. All three instruments imaged
the aurorae using a variety of wavelengths, thus quantitatively
mapping their power over the polar regions.

Multiple images acquired regularly over short periods of time
spanning minutes to hours will characterize the transient nature of
auroral phenomena. Correlations of auroral activity with underlying
hazes will help our understanding of the role aurorae play in
generating polar hazes and clouds.

ORS: Imaged Tethys from 415,000 km away at a dark phase angle of 162
degrees.

MAPS: Engaged in a campaign to measure the vertical structure and
dynamics of the inner magnetosphere as Cassini crossed Saturns
equatorial plane nearly tangent to the L-shell set of planetary
magnetic field lines.

Jan. 5, DOY 005:
The polar dynamics study of the last several days continued with
attention shifted to the south pole. The south polar region is about
to enter more than a decade of polar winter. One goal of these
observations is to track the winds and determine vertical cloud
structure in the dynamic polar regions. Simultaneous observations by
ISS and VIMS provided the opportunity to solve for cloud heights
using two independent measurements: by absorption by methane gas
above the clouds from ISS, and by thermal emission at various
wavelengths from VIMS.

Friday, Jan. 2 (DOY 002):

Seven Instrument Expanded Block files (IEB) were uplinked to the
spacecraft in preparation for the start of S47 execution next week.
An additional IEB will be sent up tomorrow, and the background
sequence itself will go up on the 7th.

Monday, Jan. 5 (DOY 005):

An Uplink Readiness Review for the propulsion system fuel-side
repressurization activity was held Jan. 5.  The command files have
been tested, procedures have been finalized and approved, and the
Spacecraft Team is prepared for the activity.  The first commands
will be uplinked to the spacecraft tomorrow.

Update: Activities began on Jan. 6, with the lowering of fault
protection thresholds for the Overpressure-1 and Overpressure-2
System Fault Protection algorithms.  This was successfully done and
brings the fault protection thresholds to levels consistent with the
remaining mission bi-propellant levels.

The final sequence approval meeting for S47 was held today along with
the kickoff meeting for the Saturn/Rhea live update.  The ORS
instruments have given their Go so the teams will now begin to build
the files for uplink on Jan. 10.

Tuesday, Jan. 6 (DOY 006):

Port 2 products were delivered today as part of the S50 Science
Operations Plan (SOP) Implementation process. A kickoff meeting was
also held today for S51 SOP.

Most of today was devoted to the first of three compositional studies
of Saturns atmosphere led by CIRS with UVIS and VIMS participating.
These measurements require lengthy integration times at a single
point on Saturn.

Visit the JPL Cassini home page for more information about the
Cassini Project: http://saturn.jpl.nasa.gov/>
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