Cassini Significant Event Report

For Week Ending 09/24/04

The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Wednesday, September 22. 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 .

Activities for the currently executing sequence S04 included approving and uplinking numerous files, including files for probe battery depassivation, resetting of probe relays, an Instrument Expanded Block for the Ion and Neutral Mass Spectrometer (INMS), and real-time commands for the Magnetospheric Imaging Instrument (MIMI) and the Cassini Plasma Spectrometer (CAPS).

On Sunday, the first battery depassivation sequence was executed on the Huygens probe. The purpose of the depassivation activity is to remove the thin layer that forms within the lithium-sulphur-dioxide battery cells on the surface of their electrodes. This layer, which builds up naturally over time, helps the cells to retain their charge during the long Cassini cruise phase but is undesirable for operations during the Probe mission

The sequence powered on the probe using orbiter power as usual but then sequentially brought each of the five probe batteries on line for five minutes. This was the first time the batteries' performance has been monitored since before launch. The activity was completely nominal and indicates that all five probe batteries are healthy and ready to support the complete Huygens mission including the pre-heating option. The second depassivation activity is scheduled for December 5.

Other on-board activities this week included a Radio Science Subsystem (RSS) Periodic Instrument Maintenance activity, a characterization of the Ultra-Stable Oscillator, and a calibration of the High-Gain Antenna boresight. This is the first time RSS has used an Inertial Vector Definition file to produce and implement an actual spacecraft activity. The activity was performed successfully.

The Imaging Science Subsystem (ISS) focused on long duration movies looking for ring 'spokes.' Magnetospheric and Plasma Science (MAPS) instruments continued to search for upstream plasma activity and monitored the solar wind. Optical Navigation took images twice a day to refine Cassini's trajectory and improve knowledge of the satellites' orbits.

In the last week, 1064 Imaging Subsystem (ISS) images were received along with 70 Visual and Infrared Mapping Spectrometer (VIMS) cubes. Since Approach Science began in January of this year, 22291 ISS images and 5309 VIMS cubes have been returned.

An official port 1 delivery was made this week for the Science Operations Plan (SOP) Implementation process for tour sequences S37/S38, and the official port delivery was made as part of the S07 SOP Update process. The team files have been merged for both deliveries and a report published identifying any issues. The wrap-up meeting for the SOP Implementation process for tour sequences S37/S38 was held on 9/22/04 and these products will be archived for later use. The SOP Implementation process for tour sequences S39/S40, as well as the SOP update process for tour sequence S08, began on the same day.

Sequence development continued for S05 this week with a Sequence Change Request (SCR) and Waiver Approval meeting where five SCRs were approved. Preliminary inputs from all teams were also due this past week. Results from the RADAR Team's analysis of the Integrated Test Laboratory (ITL) tests for the Ta flyby show that the actual pointing profile generated in the test matches very well with the intended design.

The Spacecraft Operations Office (SCO) held the Attitude Control Flight Software A8.7.1 Uplink Readiness Review on September 20, 2004. This flight software load contains updated parameters necessary for the Probe Mission and beyond. The A8.7.1 flight software is due to be uplinked to the spacecraft Solid State Recorders starting September 28, with the checkout starting October 2, 2004.

An operational delivery of Navigation software version T1.5 was made to the project on 9/22/04.

A Sequence/Software Monthly Management Review was held on 9/16/04. Status was provided on probe sequence development as well as software status from Attitude Control Subsystem, Navigation, Mission Sequence Subsystem, and Mission Support & Services Office.

For the most recent Cassini information, press releases, and images, go to