Cassini Update - February 9, 2007

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Cassini Significant Events
for 01/31/07 - 02/06/07

The most recent spacecraft telemetry was acquired Tuesday, February 6, from
the Goldstone tracking complexes. 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 .

Wednesday, January 31 (DOY 031):

An instrument flight software update delivery coordination meeting was held
today for Composite Infrared Spectrometer (CIRS) version 5.0.  The update
included four new CIRS internal commands, added ability to pre-filter raw
data, and added additional items to housekeeping telemetry.  

A time-lapse movie of Cassini crossing Saturn's ring plane is Astronomy
Picture of the Day today. 

Science observations on Wednesday included Ultraviolet Imaging Spectrograph
(UVIS) observations of the occultation of a star by Enceladus.  Saturn's
moons Tethys and Rhea were imaged for optical navigation use.

Thursday, February 1 (DOY 032):

The final plenary session of the Cassini Project Science Group (PSG) meeting
concluded at 4:00 today.  The attending group of scientists and flight team
members were able to narrow the selection of a tour extension trajectory
down to three candidates.   Those three were then passed off to members of
the PSG Executive Session to make the final selection.  Tour PF6h9 was the
selected tour.  On Feb. 15, the Program will present a proposal to NASA for
a continuation of the Cassini mission beyond its current nominal plan of
four years.  The presentation will include an overview of the selected tour
and science rational for an extended mission.

The Media Relations Office has issued an image advisory on an infrared image
taken by the Visual and Infrared Mapping Spectrometer (VIMS).  On Dec. 29,
2006, VIMS imaged a giant cloud on Titan half the size of the United States.
Scientific models had predicted this cloud system, but it had never been
imaged in such detail before. The same cloud system seen on Dec. 29 was
still there two weeks later during a Jan. 13, 2007, flyby, even though
observing conditions were slightly less favorable than in December.  The
cloud may be responsible for the material that fills the lakes discovered
last year by the RADAR instrument.  For the full story and associated images
link to:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=720

Two different types of observations today focused on the high latitudes of
Saturn. The Imaging Science Subsystem (ISS) used photopolarimetry to study
the physical properties of particulate matter in Saturn's atmosphere by
measuring the intensity and polarization at different wavelengths. VIMS made
simultaneous observations.

Periapsis of orbit 38 was at 2007-032T09:57:52 at a distance of 15.6 Rs. The
Radio and Plasma Wave Science (RPWS) instrument took advantage of the
proximity at periapsis to observe Saturn Kilometric Radiation (SKR) at
millisecond resolution to characterize its temporal structure.

Outbound from periapsis, ISS, CIRS, and VIMS began a campaign to try to
catch a spoke forming on the rings near the morning shadow edge at a ring
radius of 110,000 km.

Friday, February 2 (DOY 033):

A non-targeted flyby of Titan occurred today. For this flyby RADAR turned
its attention toward the satellite for radiometer data of the southern
latitudes.

Optical navigation images were taken today of Rhea and Enceladus.

Saturday will provide an opportunity to observe Dione at low phase and even
at zero-phase. In this geometry, since phase angle measures the angle from
Sun to satellite to Cassini, there are no shadows on the surface. As the
phase approaches zero, the observing instruments see an opposition surge in
which the target brightens far more than would normally be expected.

Also on Saturday, ISS will observe a transit of Saturn's moon Mimas in front
of the much smaller Helene. The exact time when the satellites are aligned
in the instrument's field of view helps to refine determination of their
orbits.

Sunday, February 4 (DOY 035):

Early in the day, Cassini crossed through the ring plane from south to north
at approximately 20Rs from Saturn. The MAPS (Magnetosphere And Plasma
Science) instruments used this crossing to measure the vertical profile of
the Titan torus. The opportunity will be repeated at this distance but in a
descending crossing on the 16th of February.

Saturn with all of its rings and its satellites Dione and Telesto were
captured together in a single image. Tethys, Mimas, and Epimetheus starred
in another image with the rings. Mimas was the object of an optical
navigation image.

Monday, February 5 (DOY 036):

The A8.7.5 Attitude and Articulation Control Subsystem (AACS) flight
software (FSW) patch has been declared to be a success.  While the FSW
upload procedures would occur over a week of prime and backup passes, the
A8.7.5 parameter updates involved months of planning, testing and reviews.
Many hard hours of work and effort were invested to mitigate any risk
involved in patching the FSW, which now resides on the Solid State Recorders
(SSR)s and AACS Flight Computers (AFC)s. This load changed parameters and
vectors only.  There were no logic changes.  Changes included:

     Default thruster magnitude updates,
     Default secondary safing vector pair for window Feb. - Dec., 2007,
     IRU-A scale factor updates,
     Phantom momentum-related FP parameter updates.

Still on the slate to wrap up events for this update is the first in-flight
IRU-A gyro calibration with the new scale factor values on Feb. 27. The FSW
normalization involving the copying of AACS FSW A8.7.5 from the non-default
to default partitions of the SSR is scheduled to occur on March 4, 2007.
The next AACS FSW update, version A8.7.6, is coming up in January, 2008.  

Tuesday, February 6 (DOY 037):

Dione was the first target of observations today with CIRS observing in the
infrared and UVIS in the ultraviolet.  An image was taken of each of
Enceladus, Epimetheus, Atlas, Prometheus, and Pandora for orbit
determination purposes.  Attention then turned from satellites to rings.
VIMS made a 3x1 mosaic of each ansa of the rings. UVIS observed an
occultation of the star Psi Cen by the rings.

Cassini outreach presented an overview of "Reading, Writing & Rings" at JPL
to a group of 60 after school educators from disadvantaged schools
participating in the Collaborative After School Project (CASP). The Project
is dedicated to fostering developmentally oriented learning experiences for
children and youth during the after school hours.  For more information link
to:

http://www.csupomona.edu/~casp/index.html

The sequence leads for S28 have reported that after the last merge of input
products, the sequence size was over the memory limit by 4128 words.  A time
to split the sequence into Parts A and B has been selected on DOY 074.
Requests have been sent to all participants to let the leads know by Feb. 7
if there are any concerns or issues with the selected time.  The uplink of
S28 files to the spacecraft begins next week.  S28 begins execution on Feb.
17.

A kick-off meeting has been scheduled for Thursday for a live update for
VIMS and RADAR observations of Hyperion.  Based on the post OTM-93
trajectory, the Hyperion errors are much smaller than last week but still
substantial. An update currently seems wise. 

The sequence leads for the S30 Science Operations Plan Update process
received the products for the official input port today.  The products will
now be merged, sent to the Spacecraft team for review, then posted to the
official file repository for review.

A delivery coordination meeting was held today for Cassini Radio Science
Predicts software version 3.0.  The purpose of the program PREDICTS is to
predict the radio frequencies to be received by the Radio Science Receiver
(RSR) as a function of time.  The Radio Science System Group at JPL uses
this program for receiving data during operations pertaining to Radio
Science experiments. The Cassini Radio Science Operations Team uses it for
specific Cassini operations pertaining to Cassini Radio Science experiments.

Now that the project has selected a tour to fly for extended mission, the
question arises, what next?  This was the topic discussed at the Mission
Planning Forum this week.  Specific items included receipt of tweak
requests, how much time should be allocated to the requests, review, and
final analysis, TOST jumpstart results, and generation of the reference
trajectory for the extended mission.  A draft schedule was presented with
dates for these and other milestones.

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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