Status Report

Cassini Weekly Significant Events 12/20/00 – 01/03/01

By SpaceRef Editor
January 6, 2001
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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 successful.
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 period.
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:
Cassini 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, Calif., manages the Cassini mission for NASA’s Office of Space Science, Washington, D.C.
Cassini Outreach
Cassini Mission to Saturn and Titan
Jet Propulsion Laboratory
California Institute of Technology
National Aeronautics and Space Administration

SpaceRef staff editor.