Cassini Significant Event Report

For Week Ending 03/19/04

The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Monday, March 15. 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 .

Instruments continue to monitor the solar wind as it approaches Saturn, and to take images that will be used to make approach movies. The Ultraviolet Imaging Spectrograph (UVIS) continues to obtain data to produce a map of Saturn's magnetosphere.

Additional onboard activities include loading of Visual and Infrared Mapping Spectrometer instrument expanded blocks (IEB) and flight software (FSW) version 8.1, loading the Ion and Neutral Mass Spectrometer build 3-4 FSW to the SSR and build 4 FSW to RAM, uplinks of a Cosmic Dust Analyzer parameter update, Probe Mission Timer Unit test mini-sequence, Magnetospheric Imaging Instrument (MIMI) parameter update, lowering of MIMI collimator voltages and collimator off, uplink of Cassini Plasma Spectrometer commands to power on and perform high voltage sensor testing, and clearing of the ACS high water marks.

A series of Radio Science Subsystem (RSS) engineering activities took place this week. They included an Ultra Stable Oscillator (USO) characterization test, a High Gain Antenna (HGA) Boresight Calibration, and a Ka-band Translator recovery attempt. The USO test and Boresight Calibration were nominal except for some unexpected signal strength variation during the boresight activity over DSS-25. All data were successfully acquired. The Ka-band Translator (Kat) has been powered OFF since October 6, 2003. The recovery procedure consisted of sending real-time commands that were timed for execution after the completion of the USO test and Boresight cal. After the first KaT power ON, the free running signal was observed to be approximately 17.75 MHz above the nominal frequency, which is higher than previously observed "bad regions."

The RADAR team successfully tested the Titan A (Ta) encounter Instrument Expanded block. Except for a few missing frames, all data were recovered from the downlink and processed through Level 0 and Level 1A software. A procedure for retrieving the data within 1 hour of the last radar data arriving at the ground worked well; there were no differences between this quickly retrieved data and "final" data three days later. This will be very beneficial during Ta in giving the processing team an additional five hours to work with the data before a press conference compared to the previously planned retrieval procedure.

Science Operations Plan (SOP) Implementation for tour sequences S23/S24 wrapped up this week. The sequences have been archived and will be dusted off again in May 2006. The Official Port 1 delivery for S25/S26 was met, and a kick-off meeting was held for SOP Implementation of sequences S27/S28.

As part of continuing development of the S01 sequence, a waiver request was approved to open Latch Valves 20 and 30 earlier than usual for TCM-20, a meeting was held to discuss VIMS IEB loads during S01 sequence execution, and five sequence change requests (SCR) were approved at an SCR approval meeting.

Tour Science Plan presentation #3 to the flight team was on the Saturn Target Working Team (TWT) plans for tour. These weekly presentations are proving extremely valuable to the flight team in building understanding of activities and events that will begin in the next few months.

All teams and offices participated in this month's Cassini Monthly Management review, and in a walkthrough of the presentations to be given at the Tour Operations Readiness Review in early April.

An abstract has been submitted on an X-ray measurement of Titan's atmospheric extent from its transit of the Crab Nebula. Saturn's largest satellite, Titan, transited the Crab Nebula on 5 January 2003. This astronomical event was observed with the Chandra X-ray Observatory. An "occultation shadow'' has clearly been detected and is found to be larger than the diameter of Titan's solid surface. The difference gives a thickness for Titan's atmosphere of 880 km + 60 km. This is the first measurement of Titan's atmospheric extent at X-ray wavelengths. The value measured is consistent with or slightly larger than those estimated from earlier Voyager observations at other wavelengths. For more information go to:

Formal Education attended a one-day workshop in conjunction with the Lunar and Planetary Science Conference. This workshop was dedicated to examining the challenges and possibilities of building high school and community college science programs using actual data collected on JPL missions.

Outreach supported a science fair at Barnhart School in Arcadia, California. Over 100 students in grades 1-6 submitted science fair projects.

The latest images taken by the Cassini-Huygens spacecraft show clumps seemingly embedded within Saturn's narrow, outermost F ring. The narrow angle camera took the images on Feb. 23, 2004, from a distance of 62.9 million kilometers. The two images taken nearly two hours apart show these clumps as they revolve about the planet. NASA's two Voyager spacecraft that flew past Saturn in 1980 and 1981 were the first to see these clumps. The Voyager data suggest that the clumps change very little and can be tracked as they orbit for 30 days or more. No clump survived from the time of the first Voyager flyby to the Voyager 2 flyby nine months later. For more information go 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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