Cassini Significant Event Report

For Week Ending 04/16/04

The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Tuesday, April 13. 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 activities on-board for the duration of C44 include repetitive blocks of imaging with occasional riders, a few Ultraviolet Imaging Spectrograph system scans and a sprinkling of optical navigation (OPNAV) images. The results will be Saturn approach movies to study the planet's atmosphere and its temporal variations, searches for new satellites, observations of Titan, searches for diffuse ring material and system scans to map atomic species.

The Cosmic Dust Analyzer performed the first time event of rocking downlinks this week. All subsystems reported normal performance and results are undergoing evaluation. Additional on-board activities included a Radio and Plasma Wave Science High Frequency Receiver Calibration and an ACS Reaction Wheel Assembly bias unload.

Development of S01, the first tour sequence, continued this week with a waiver for SSR Data Load command timing constraints for OPNAV IEB loads approved at the Preliminary Sequence Integration and Validation (PSIV) waiver disposition meeting. This concluded the PSIV1 development phase. PSIV2 began with a sequence change request approval meeting. Thirty-two change requests for the sequence were dispositioned.

Development of the S02 tour sequence began this week. A kick-off meeting was held, merged reference activity plan files containing the Inertial Vector Propagator and Star ID suspend commands delivered, and the remaining engineering commands, science activities, and Sub-Sequence Generation Spacecraft Activity Sequence Files released.

The flow of science planning processes for tour goes from Science Operations Plan (SOP) Implementation, to Aftermarket, and on to SOP Update. This week, there were significant development milestones in all processes for multiple tour sequences.

A wrap-up meeting for implementation of tour sequences S25 and S26 was held. The sequences have now been archived and will begin the Aftermarket and SOP Update processes in the summer of 2006. In addition, official input port #1 for SOP Implementation of tour sequences S27 and S28 occurred this week. The delivered sequence products were merged and handed off to the ACS team for a complete end-to-end pointing analysis.

At the Aftermarket Assessment meeting for S04, it was determined that very few changes had been submitted by participating teams. As a result, it was decided that the Decision Meeting was to be canceled and all requested changes approved unless the Saturn target working team identifies any major issues in incorporating the requested changes.

Most waiver requests were approved at the S02 Project Briefing and Waiver Disposition meeting. A few were delayed until an end-to-end C-kernel could be delivered that included the attitude profile during the Saturn Orbit Insertion (SOI) burn period. This process has now been completed and a hand-off product was delivered to Uplink Operations for the start of the Science and Sequence Update process. In addition, a kick-off meeting was held for S03 SOP Update. The scheduled Science Adaptation Panel (SAP) meeting was canceled as all requested DSN station coverage for this sequence has been received.

In the last week, 275 Imaging Science Subsystem (ISS) images and 23 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 2888, and the number of cubes up to 697.

The Cassini Program completed a two day Tour Operations Readiness Review. The objective of the review was to evaluate the readiness of the Mission Operations System and Ground Data System to support Tour operations. All teams both at JPL and remote sites presented their readiness status. The board agreed that Cassini was well prepared for tour, and that the work remaining was appropriate.

The Operational Readiness Test #1 for Saturn Orbit Insertion (SOI) began last Friday in the Integrated Test Lab. This test is the dry run of all nominal events that will start for real on June 2 and continue through July 3, 2004. This week the test covered loading the sequence onto the Solid State Recorders and performing Trajectory Correction Maneuver #21.

An ACS Flight Software (FSW) Review/Certification Requirements meeting was held this week. The FSW was accepted for operational use with two follow-up documentation actions assigned. A8.6.7 will support SOI, and another planned FSW build/parameter set, A8.7.0, is scheduled to support the Huygens probe mission. An uplink readiness review for A8.6.7 will be held next week.

The ACS team gave a presentation to the Cassini Project at the Mission Planning Forum on the use of a hybrid ACS control system. This is a future potential contingency. The presentation explored the spacecraft capabilities when operating with a reduced set of reaction wheels and using Reaction Control Subsystem thrusters for selected axes.

The Navigation team gave a presentation and recommendations at the Forum concerning modifications to the reference trajectory. This was a revisit of the implications of raising the T3 altitude and subsequent trajectory and flyby altitude changes.

Multi-Mission Image Processing Laboratory (MIPL) conducted a test of the critical OPNAV downlink process. The test involved automated queries of the Real-time stream and, in parallel, the more manual contingency process. The automated process stopped early and delivery was delayed by a restart. The contingency process worked as planned and Navigation received the data within 30 minutes of initial receipt by MIPL.

Three months before Saturn arrival, the Cassini spacecraft caught two storms in the act of merging into one larger storm. This is only the second time this phenomenon has been observed on the ringed planet. A series of Cassini images documenting this event is available on the Internet at .

On 14 April 1629, 375 years ago, the Dutch scientist Christiaan Huygens was born. The European Space Agency (ESA) probe on-board the NASA/ESA/ASI Cassini-Huygens mission to the Saturnian system is named after this lens-maker who discovered Titan in 1655. For more information on Christiaan Huygens and the anniversary of his birth 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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