Cassini Significant Event Report

For Week Ending 01/05/01

The most recent spacecraft telemetry was acquired from the Goldstone
tracking station on Wednesday, January 3. The Cassini spacecraft is in
an excellent state of health and is operating normally. The speed of the
spacecraft can be viewed on the
"Present Position"
web page.

On Tuesday December 19, the C23 sequence was halted with the program
remaining on board, instruments placed in a safe configuration, and the
spacecraft directed to Earth point in response to the autonomous swap from
reaction wheels to thrusters for attitude control that occurred on
December 15. Attitude Control engineers performed a series of in-flight
diagnostic tests to further understand the performance of the second
reaction wheel that had exhibited larger than expected drag during the
previous week's observations. All tests were nominal. Extensive
discussions with the wheels' manufacturer and JPL experts were undertaken
and it is believed that the likely cause of the autonomous shutdown of the
wheels was inadequate distribution of lubrication in the bearings due to
extended operation at low speeds.

On Thursday, December 21, the spacecraft was returned to RWA control, but
only to maintain Earth pointing without resuming the science sequence.
The wheels were monitored for the next six days with no problems
observed. Additional activities in this period included Command & Data
Subsystem (CDS)-A and CDS-B Autonomous SSR Memory Load Partition Repairs,
Attitude and Articulation Control Subsystem (AACS) SPOT LIST Memory
Readout (MRO) to read out additional data from the AACS Extended Body Star
ID test, AACS Highwater Mark clears, and enabling of Ultraviolet Imaging
Spectrometer (UVIS) Science Data.

On Thursday, December 28, the C23 background sequence was reactivated.
Real-time activities included playback pointer reset to recover the
previous night's "observation" period, Composite Infrared Spectrometer
(CIRS) to Science Mode, C23 Background Sequence / SSR overlay
Mini-sequence Activation Immediate/Delayed Action Program (IDAP), RWA2
Bias Overlay IDAP, Imaging Science Subsystem (ISS) and Ultraviolet
Imaging Spectrometer (UVIS) Instrument Expanded Block (IEB) Loads, and
AACS Highwater Mark clear. All commands were verified to be successfully
received at the spacecraft. The expected telemetry mode change was
observed by project personnel along with spacecraft slew start back to
Jupiter at the correct time indicating correct initiation of the
background sequence.

Saturday, December 30, began the Phase E portion of C23. Activities
included Jupiter Observations of the Rings at 60 degrees phase angle,
Atmospheric cyclic, CIRS Feature Track, and Ring Plane Crossing. Jupiter
closest approach occurred at 02:04 PST, Spacecraft Event Time. This was
followed by IO Eclipse imaging activities, Europa imaging activities,
uplink of IEB loads for ISS and VIMS, Jupiter Rings (75 degree phase
angle) observation, CIRS Feature track observation, imaging activities of
Europa and Ganymede, Cassini Plasma Spectrometer (CAPS) Solar Wind
activity, AACS Highwater Mark Clear, RWA #2 Overlay bias for DOY 004,
Radio Science Ka-Band transmitter OFF and RADAR Power On, and the RADAR
Synchrotron Radiation activity.

The big event for RADAR during the next three months is the observation of
Jupiter's synchrotron emission. This observation will be done jointly in
space and on the ground using Cassini, the Deep Space Network (DSN), and
the Very Large Array (VLA) antennas. The Radar observations of Jupiter
serve two separate purposes. First, Jupiter offers a unique opportunity to
calibrate the radiometer. Because of the proximity of the spacecraft to
Jupiter, the Jovian atmospheric thermal emission will fill the antenna
beam providing the basis to calibrate the radiometer system. The
calibration is further enhanced by simultaneous multi-band observations by
the DSN. The second purpose is related to observations of Jupiter's
synchrotron emission. Jupiter's synchrotron emission originates with the
relativistic electrons trapped in Jupiter's inner radiation belts. This
emission has been studied by radio telescopes at various frequencies since
the 1960s. Monitoring by the DSN and synchrotron emission maps by the VLA
significantly advanced the understanding of Jupiter's magnetosphere in
recent years. Cassini offers an opportunity to observe and map the
synchrotron emission at a new frequency (13.8 GHz) not possible from Earth
based telescopes. A preliminary review of the data indicates that the VLA
observations were successful. Preliminary maps of Jupiter (and the
synchrotron emission) at 20 and 90 cm wavelengths have been generated.
Cassini Radar observations are at 2cm (for reference). Both the 90 and 2
cm observations are new results, although some work has been done in the
past at 90 cm (but without the full capabilities of the VLA). A total of
89,902 RADAR Science SABs (data packets) were received.

Instrument Operations and the Multi Mission Image Processing Laboratory
have produced and delivered 15910 ISS images (10251 Narrow Angle Camera
and 5659 Wide Angle Camera), and 1915 VIMS cubes since the start of the
Jupiter encounter period.

CDA reported that their observation of the Jovian dust stream phenomenon
as part of the joint Galileo-Cassini dust stream investigation was

Radio and Plasma Wave Science (RPWS) personnel have observed numerous
outbound and inbound bow shock crossings from December 28 through January
3. CAPS ion data and electron data also confirm crossings throughout this

The Preliminary Sequence Integration & Validation (PSIV) approval meeting
was held this week for Cruise 24. Cruise 25 is still in the Sub Sequence
Generation (SSG) phase. The first post-Jupiter Science Planning Virtual
Team (SPVT) work for C26 started this week. This activity will follow the
new eight week development schedule for cruise sequences. The C26
sequence covers the period from April 30, 2001 through July 8, 2001.

Outreach presented "Jupiter in Myth, History, and Science" to a
standing-room-only crowd at Pasadena City College on December 30. The
production included a reading of Ovid's creation myth involving Jupiter,
King of the Gods, an appearance by Galileo Galilei, a presentation on the
development and current level of understanding of Jupiter as a planetary
system, and a live telephone call from Sir Arthur C. Clarke to mark the
turn of the millennium.

The "Saturn Educator Guide," which has been available for download for
several months, is now available in printed and CD-ROM versions.

KCET's "Life and Times" featured Cassini and Galileo Jupiter science
results this week. An article on the joint Cassini / Galileo observations
of Jupiter appeared in the L.A. Times and is available at:

HREF=",+while+older+one--long+after+its+expected+demise--keeps+transmitting+data.">Fluke Gives Scientists Double Look at Jupiter; Space: New craft arrives, while older one--long after its expected demise--keeps transmitting data.

Additional information about Cassini-Huygens is online at

Cassini will begin orbiting Saturn on July 1, 2004, and release its piggybacked Huygens probe about six months later for descent through the thick atmosphere of the moon Titan. Cassini-Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Office of Space Science, Washington, D.C.

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