Cassini Significant Events for 01/19/06 - 01/25/06 The most recent spacecraft telemetry was acquired Wednesday, January 25, from the Goldstone tracking stations. 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 http://saturn.jpl.nasa.gov/operations/present-position.cfm . Thursday, January 19 (DOY 012): A Program Control Change Board Review was held today to examine three Engineering Change Requests. The Cassini Program Manager approved "Maneuver Automation Software V6.0 Requirements," "Cassini Coherency Transition Playback Delay Tool Design," and "Remote Access Multi-mission Processing & Ground Environment software v2.4.1 - New Features." Approval is currently pending for " Mission Sequence Subsystem D12.0 Orbit Trim Maneuver Blocks." Friday, January 20 (DOY 013): The final approval meeting for S18 was held today. Uplink of the instrument expanded block files will begin on Sunday evening, and the sequence will begin execution on January 27. Saturday, January 21 (DOY 014): A Reaction Wheel Assembly (RWA) friction test was performed today on the prime wheels, numbers 1,2, and 4. In this test, the prime RWAs are spun up to 900 RPM in both directions and are timed as they spin down to 0 RPM. This gives an indication of RWA performance. The longer the spin down time, the better. The results of the test today were favorable. As compared to early 2004, RWA-1 showed a positive trend, RWA-2 showed no significant change, and RWA-4 showed only a slight negative trend. The RWA-1 results are particularly gratifying since it has recovered nicely from the big friction spike observed in 2004. The prime RWAs are tested every three months, and the backups are tested every six months. A test of the backup wheel is scheduled for January 26. Monday, January 23 (DOY 016): High winds at JPL forced the facility to close early due to potential wind hazards e.g., broken trees, loose building materials, etc. The Laboratory was closed to off-site visitors including the 110 Cassini scientists who were to visit for the 38th week-long Project Science Group (PSG) meeting. Although it was necessary to cancel the working group meetings planned for today, the PSG was able to resume with the plenary session scheduled on Tuesday. A member of the Spacecraft Operations Office Attitude Control Subsystem will present "In-Flight Estimations of Cassini Spacecraft Inertia Tensor and Thruster Magnitude" at the AIAA/AAS Space Flight Mechanics Conference in Tampa, Florida, this week. Instrument Expanded block files for S18 and the background sequence were uplinked to the spacecraft today by the sequence leads. This morning the Spacecraft Operations Office received an email from the DSN notifying the Cassini Program that at present, the DSS-15 X Maser is red due to difficulties coming back from a power outage at Goldstone this morning. It may not return to operation until DOY 032. The S18 passes on DOY 029, 030, and 031 use DSS-15. In its current condition, the telemetry rates in the S18 background sequence cannot be supported and would need to be reduced to 27650 bps. This would leave an excess of just over 1 Gb of data volume over the three days. It is possible to carry over the data until DOY 036 when the SSR would be overfilled. Station personnel are attempting to fix the problem. In the mean time, Cassini Science Planning is working the issue with the instrument teams, the sequence leads are examining possible customization of the background sequence and the generation of contingency files to drop the telemetry rates, and the DSN schedulers are hunting for a window where 70M coverage could be provided in which we could retrieve the data. Wednesday, January 25 (DOY 016): This week science observations included ISS spectrophotometry and phase coverage of Dione, Enceladus, Iapetus, Mimas, Rhea and Tethys. For Iapetus, ISS also obtained good limb topography and geodesy coverage along with a good global color observation. The Ultraviolet Imaging Spectrograph (UVIS) rode along with these ISS observations to measure the ultra-violet albedo across a range of longitude and phase. Wrap up: Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest press releases and images. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. JPL designed, developed and assembled the Cassini orbiter. --- To unsubscribe from Cassini Spacecraft Updates, send a message to leave-cassini-@xxxxxxxxxxxxxxxxx --- Visit the JPL Cassini home page for more information about the Cassini Project: <http://saturn.jpl.nasa.gov/>
