Cassini Significant Event Report

For Week Ending 07/23/04

The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Wednesday, July 21. 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 .

On-board science activities this week included solar wind measurements by the Magnetospheric and Plasma Science (MAPS) instruments, Ultraviolet Imaging Spectrograph (UVIS) observations of Saturn's aurora and inner magnetosphere, and Imaging Subsystem observations of the southern hemisphere of Iapetus.

Spacecraft activities included a reaction wheel assembly bias and the removal of the Saturn Orbit Insertion critical sequence from the SSRs. This activity involved the uplink of several real-time commands over a period of three days. The procedure executed normally.

The Cosmic Dust Analyzer discovered a dust particle carrying an electrical charge of almost 10 fC at a Saturn distance of 26 Rs and -16 degrees latitude. This is the first such detection in the Saturn environment, and the first since detection of particle charges in 2000. The charges of previous interplanetary particles were below 4 fC. The signal detected now is more than two times stronger and it is well above the detection threshold of about 1 fC.

Science Operations Plan (SOP) Implementation of tour sequences S31/S32 has completed and a wrap up meeting is scheduled for next week. Official port#1 for SOP Implementation of S33/S34 occurred with the delivered files merged and the resulting products delivered to ACS for end-to-end pointing profile analysis. SOP Implementation for S35/S36 began this week.

SOP update preliminary port#1 for tour sequence S05 occurred this week. The files were merged and a report identifying problem areas to be worked was generated and distributed to the team.

The Integration and Test Laboratory has begin retesting the Probe Relay and Release sequences. This activity will be ongoing for several weeks.

At the final sequence change request and waiver disposition meeting for S03, it was determined that a re-evaluation of star ID (SID) suspend commanding built for the sequence was needed. As there was margin remaining in the development schedule, it was decided to slip delivery of the final products, receipt of review of final products, delivery of the final package, and the final approval meeting by two days. ACS analysis subsequently showed no issues related to SID Suspend commanding. Final sequence products are now available, and the final Sequence Integration & Validation package has been distributed to the team. A command approval meeting (CAM) was held to approve 7 of the 9 instrument expanded block files to be uplinked to the spacecraft prior to the start of S03. The remaining files will be CAMed later in the week.

A delivery coordination meeting was held this week for Telemetry, Tracking, Command & Data Management software v28.2.1. A Software Review / Certification Requirements meeting was held for Ion and Neutral Mass Spectrometer 9.0 flight software (FSW). This delivery includes the functions in an FSW patch that was applied during C44 and S01, as well as double buffering of the bus interface unit (BIU), use of DTSTART interrupt, and writing status information to BIU memory. The FSW was accepted for operational use with one follow-up action item. The software is scheduled to be uplinked to the spacecraft on September 1.

On July 21, Cassini once again provided an image that was used as Astronomy Picture of the Day. This spectacular picture of the shadow of Saturn on the rings, along with all the most recent images may be viewed at and

Image Advisory: 2004-182

Cassini Exposes Saturn's Two-Face Moon

The moon with the split personality, Iapetus, presents a perplexing appearance. One hemisphere of the moon is very dark, while the other is very bright. Scientists do not yet know the origin of the dark material or whether or not it is representative of the interior of Iapetus. The most recent images of this intriguing satellite are available on the Cassini web site.