Cassini Significant Event Report

For Week Ending 06/11/04

The most recent spacecraft telemetry was acquired from the Goldstone tracking station on Wednesday, June 9. 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 instrument activities this week included continuation of Ultraviolet Imaging Spectrograph (UVIS) mapping of the Saturn magnetosphere in neutral and ion photon emissions. The purpose of this activity is to derive the distribution and density of atomic and molecular species. The suite of Magnetospheric and Plasma Science (MAPS) instruments continued its survey of Saturn's magnetosphere, in particular looking for upstream solar wind conditions and wave phenomena as we approach Saturn's bow shock. The Imaging Science Subsystem (ISS) continued data collection for a Titan movie that documents evidence of cloud motion that will be used to measure winds.

Additional instrument activities included a Radio and Plasma Wave Science High Frequency Receiver Calibration, a Cassini Plasma Spectrometer Power-On-Reset mini-sequence, periodic instrument maintenance of the Radio Science Subsystem, and Visual and Infrared Mapping Spectrometer (VIMS) instrument expanded block #3 SSR load, cleanup, verification, and memory read out.

Spacecraft activities included power cycling of Reaction Wheel Assembly (RWA)-1, uplink and execution of an RWA bias for Phoebe, and an ACS post Trajectory Correction Maneuver (TCM)-20 mass properties parameter update.

In support of the upcoming Phoebe flyby, the first "Live Update" process was executed and the output products uplinked to the spacecraft.

While the knowledge of the spacecraft trajectory and the various bodies in the Saturnian system are known well enough in advance that science activities can be planned, in some cases the detailed position knowledge isn't known well enough to ensure that the goals of the science teams are met. In these cases, the Live Update process is used. For this process the desired activity design is loaded to the spacecraft with "default" timing and pointing data to ensure basic science return. Then, just before the encounter the most recent Navigation knowledge is used to update that default timing and pointing to maximize the science return.

The Live Update process is especially needed with the Phoebe flyby. This target is so small and faint when viewed from the ground that the only targeting data available is from Cassini as it approaches closer and closer. This data provides the navigation team sufficient insight to make accurate trajectory predictions that meet the science needs.

Closing in on the Phoebe flyby, members of the Cassini Navigation team worked every day after TCM-20 to collect, reduce, and analyze spacecraft and Phoebe position data, and to evaluate the remaining position uncertainty against the pointing knowledge requirements. On Sunday, June 6th, the team was confident that they had good enough data to commence with the update process, and the updated trajectory files were released to the project.

The science teams then took those files and assessed the impact to their activities if the update were to be executed or not. Agreement was reached at the Live Update Go/No Go meeting that the update was both warranted and the Navigation knowledge was sufficient to meet the science intent. A "go" was then given for a continuation of the process and the Sequence Team executed the update.

There is no DSN track on Friday June 11 when the Phoebe encounter actually occurs. The flight team is eager with anticipation for the results of the flyby that will be downlinked over the Madrid and Goldstone DSN complexes on Saturday June 12.

A NASA News Release, 2004-145 June 9, 2004, entitled "Cassini Spacecraft Near First Stop in Historic Saturn Tour" giving more information on the flyby itself can be found at: In addition, Aviation Week & Space Technology June 7, 2004 has published an article on Phoebe and the TCMs that are getting us there.

Background sequence products were released as part of the Preliminary Sequence Integration and Validation (PSIV) 2 cycle for tour sequence S02, and a final SIV sequence change request and waiver approval meeting was held.

Preliminary port#2 for Science Operations Plan Implementation of tour sequences S29 and S30 occurred this week along with preliminary port #1 for S31 and S32. The products have been merged, checked and any problems reported to the teams.

As part of the Science Planning aftermarket process, all requested changes to the S06 sequence were delivered this week. An assessment meeting will be held on June 14.

In the last week, 500 ISS images were obtained and were distributed along with 875 VIMS cubes. The total number of ISS images acquired since the start of Approach Science is now 10219, and the number of VIMS cubes is 3217.

As reported at the last Cassini Project Science Group meeting, the Cosmic Dust Analyzer (CDA) instrument has discovered dust storms from Saturn! The detected particles are tiny and fast, similar to the dust stream particles from Jupiter. They appear not only directly from Saturn, but can be detected as far as 100 degrees off from the direct Saturn-CDA direction.

NASA and European Space Agency (ESA) officials held an arrival press conference for the Cassini-Huygens Saturn mission this week. The press conference originated out of NASA Headquarters where panelists discussed an overview of the Saturn tour, Huygens Probe mission, the Phoebe flyby, and the challenging maneuver to place the spacecraft in orbit around Saturn. Panelists included:

  • Dr. Ed Weiler, NASA's Associate Administrator for Space Science, Washington.
  • Orlando Figueroa, Director, Solar System Exploration Division, NASA Headquarters.
  • Dr. Charles Elachi, Director, NASA JPL, Team Leader for the Cassini Radar Instrument, Pasadena, Calif.
  • Robert Mitchell, JPL Cassini Program Manager.
  • Dr. Jean-Pierre Lebreton, ESA Huygens Probe Project Manager.

The Cassini arrival press kit is available to download from the Cassini website at:

In conjunction with the press briefing, the Imaging Team released two new images. One shows a colorful Saturn looming up ahead. The other indicates the radial position of Cassini's ring plane crossing relative to the main rings and some of Saturn's moons. The images can be found at

From the other side of the globe, the Imperial College of Science, Technology and Medicine, London, where members of the Magnetometer Subsystem (MAG) instrument team reside have issued a press release on upcoming Cassini activities. MAG maps the internal magnetic field of the planet, and will give a better idea of what the interior of the planet is like, how the magnetic field is formed, how it is still being generated, and some further clues about how the solar system was formed. For more information please link to:

The University of Arizona is hosting a Cassini event on June 19. For maps, directions, and more information link to:

Outreach participated in 'Scout Expo,' an event for Boy Scouts and Cub Scouts from the San Gabriel Valley Council of the Boy Scouts Association of America. Over 2,000 scouts attended the one-day event. Cassini staff members spoke about the flight project, the upcoming Saturn tour, and assisted in helping 'Bear Scouts' complete elective merits in space exploration. The Cassini Mission to Saturn and Cub Scout pack 482 from Glendora, California hosted the booth. Scout Expo took place at Santa Anita Race Track in Arcadia, California.

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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