Cassini Significant Event Report

For Week Ending 04/30/04

The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Wednesday, April 28. 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 .

This week witnessed the 6-year anniversary of Cassini's Venus 1 flyby on April 26, 1998. The flyby occurred just over 6 months after launch in October of 1997.

The primary on-board activity this week was the loading of ACS A8.6.7 flight software from the Solid State Recorder to ACS memory beginning on 26 April and completing on 28 April. ACS loaded properly and all tests were normal. Additional activities included a Reaction Control Subsystem functionality checkout, Star ID suspend checkout, and Reaction Wheel Assembly bias. All activities executed successfully. Uplinks included mini-sequences to perform Imaging Science Subsystem stray light mapping and Composite Infrared Spectrometer (CIRS) scattered sunlight observations, and Cassini Plasma Spectrometer Electron Spectrometer testing.

Teams delivered Instrument Expanded Block load files, and Preliminary Sequence Integration and Validation 2 (PSIV) merge sequence products including the background sequence and Phoebe live moveable block files were released in support of sequence development for S01.

A Subsequence Generation (SSG) Sequence Change Request (SCR) approval meeting was held as part of the development of S02. SCRs to change optical navigation pointing, adding a downlink roll on DOY 194, and shifting the time of three CIRS deep space calibrations were approved. These changes will be implemented in the PSIV1 background sequence products. The S02 PSIV1 initial merged background sequence files were released for review, and SSG detailed subsequences delivered by all participating teams.

The 34th meeting of the Cassini Project Science Group was held this week at the European Space Research & Technology Centre in Noordwijk, the Netherlands.

In the last week, 611 Imaging Science Subsystem (ISS) images and 10 Visual and Infrared Mapping Spectrometer (VIMS) cubes were returned and distributed, bringing the total of images acquired since the start of Approach Science up to 4432, and the number of cubes up to 741.

Mission Assurance convened a Risk Team Meeting this week to re-assess the remaining risks identified for Cruise, as well as those for Saturn Tour Operations. Three Cruise phase risks were annotated for retirement after Saturn Orbit Insertion. Updates to several Tour related risks were also discussed and actions are pending.

The Cassini Outreach Literacy Team announced the release of the grades 1-2 lessons. Lessons are now available on the Cassini website at:

Outreach conducted a 1/2-day workshop for the education and guest services staff at the California Science Center in Los Angeles, California. The workshop included a mission update, demonstration of education materials, and a discussion of the Cassini spacecraft using the full-scale model on display at the museum.

The Cassini Imaging Team has released a montage of Saturn images illustrating the variable appearance of the planet in four different regions of the spectrum from ultraviolet to near infrared. The pictures show the effects of absorption and scattering of light at different wavelengths by both atmospheric gas and clouds of differing heights and thicknesses. They also show absorption of light by colored particles mixed with white ammonia clouds in the planet's atmosphere. Contrast has been enhanced to aid visibility of the atmosphere. For more information link to:

A TV series called `The Planets' will air on May 4, 2004, and run for 8 consecutive weeks. It was initially produced by the BBC and aired on A&E some years ago. It has been updated, rewritten and reproduced, and will now run on the Discovery Science channel.

Clear as black and white, Saturn's moon Iapetus is two-faced. One half is dark as coal and the other is as bright as fresh linens. Astronomers have puzzled over the stark difference since late in the 17th century. New radar observations hint at what's going on, but the mystery is far from solved. For more information link to:

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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