Cassini Significant Event Report

For Week Ending 12/10/04

The most recent spacecraft telemetry was acquired from the Madrid tracking station on Wednesday, December 8. 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 .

Science observations this week focused on the Composite Infrared Spectrometer (CIRS) integration of the main rings with the mid-infrared focal planes. This will give the first detailed temperature measurements across the rings. Additionally, CIRS examined the oxygen compounds H2O and CO2 in Saturn's stratosphere as a function of latitude.

The Imaging Science Subsystem (ISS) continued to image small satellites for orbit determination, the Ultraviolet Imaging Spectrograph continued to capture mosaics of Saturn's magnetosphere, and ISS captured a 3x3 movie of the Saturnian southern hemisphere in several filters with the Narrow-Angle Camera to measure wind speeds and map the occurrence of "moist" convection.

On-board activities this week included real time commands for the Cassini Plasma Spectrometer (CAPS) to restart the master Instrument Expanded Block (IEB), update the IMS sweep table and IEB for the Titan-B encounter, and restart actuation after Probe activities in S06. All activities executed as expected. Additional real time commanding included a test of the Magnetometer Subsystem scalar magnetometer, a Cosmic Dust Analyzer (CDA) RPX calibration, and closing of the main engine cover. The cover will remain closed until after the Dione flyby on December 14.

The main event this week was the second probe battery depassivation . An initial assessment indicates that the data looks exactly the same as for the first depassivation in September of this year. The depassivation sequence lasted for 35 minutes after which there was a 5-minute pause before the Probe Safing sequence started. This lasted for 8 minutes and was run to ensure that no battery remained connected to the Probe power bus. Each battery exhibited essentially the same behavior during each of the 5 minute depassivation periods, with voltages starting at ~65V and slowly increasing to ~70V. Measurements on the bus side showed battery currents ~1.9A with a similar value being measured from the Cassini line, which indicated an equal sharing of the busload between battery and Cassini. Bus voltage was rock-solid at 28V. All Probe systems are exhibiting normal behavior.

The Cassini-Huygens program held two reviews on December 2 to support the mission commitment for the Huygens mission. The first was the Huygens Probe checkout F16 review. All probe instruments and the probe engineering systems reported and are nominal and ready to support the probe mission. The second review was an internal readiness review to assess the program's total readiness to support mission. All necessary teams, flight products, and subsystems were reported ready to support the mission.

The Mission Risk Review concluded its activities on December 6 with an updated assessment of the entry and descent studies. Refined analyses with the latest Titan atmosphere models have shown further margin in the heat shield performance. Residual action items from the November 29 review were closed. The final report will be presented on December 16.

On Tuesday the Navigation Team led a meeting to discuss the impacts of canceling Orbital Trim Maneuver 7 (OTM). The meeting was attended by representatives from Program Management, Spacecraft Operations, Science Planning, and Uplink Operations. It was determined that there was no compelling reason to perform the maneuver--delivery differences at Titan with and without the maneuver were negligible, delta-V cost was a "wash", there was negligible change to instrument pointing, and there was nothing new that OTM-7 would provide from a spacecraft perspective to make OTM-9 any more accurate. The decision was made to cancel this maneuver.

The Titan Orbiter Science Team and Huygens Science Working Team hosted a Titan-B Preview Meeting with a special Dione preview following. This was an open meeting for anyone on the project who was interested in a preview of Tb science, objectives and activities.

The Science and Sequence Update Process (SSUP) for tour sequence S07 concluded this week. A Final Sequence Integration and Validation (FSIV) Sequence Change Request (SCR) approval meeting was held with 8 SCRs dispositioned. Later in the week the fully integrated sequence products were released, and the final sequence approval meeting was held. Uplink of IEBs and the background sequence begins on December 11. S07 begins execution on December 16.

Also in SSUP, a PSIV SCR approval meeting was held for S08, and as well as a Preliminary SCR meeting where 14 SCRs were approved.

The Science Operations Plan (SOP) Update process for S09 concluded this week. A Project Briefing and Waiver Disposition meeting was held and a handoff package transferred to the Sequence Team leads. S09 has begun the Sub-Sequence Generation (SSG) phase of SSUP with a kickoff meeting held on Tuesday. The stripped subsequences were released for teams to populate, and the SSG Science Allocation Panel meeting was cancelled, as there were no DSN changes.

Official port#1 of the SOP Update process for S10 occurred last Friday. The products were merged and sent to ACS for the end-to-end pointing validation.

S11 has concluded the Aftermarket process and begins SOPU next week.

Official port #1 for SOP Implementation of S39/S40 occurred this week along with Preliminary Port #1 for S41. The team files for S39/S40 were merged and delivered to ACS for end-to-end-pointing validation. The products for S41 were merged, the preliminary port analysis performed, and reports provided to the teams.

Mission Planning has released the Titan-B and Huygens/Titan-C Mission Descriptions. The Titan-B document provides a brief, concise description of encounter events, including an estimated playback schedule for all instruments. Also included is a one-page "quick look" reference sheet. Updates to the Huygens/Titan-C document include the addition of the Probe Release timeline and an updated sequence layout chart.

A beautiful picture of Mimas against Saturn's rings and shadows was Astronomy Picture of the Day on December 2.

Cassini has an impressive collection of 131 papers being presented at the Fall AGU meeting next week in San Francisco, California.

"Cassini Captures Saturn Moon Red-Handed." The Cassini spacecraft has witnessed Saturn's moon Prometheus snatching particles from one of Saturn's rings. This and the most recent image advisory may be found on the Cassini website at

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