Cassini Significant Events for 06/01/06 - 06/07/06 The most recent spacecraft telemetry was acquired Wednesday, June 7, 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, June 1 (152): The Science Operations Plan Update process for S24 kicked off today. The process will continue for approximately five weeks, and then will be handed off to Uplink Operations for final development. Friday, June 2 (DOY 153): A friction test of the backup reaction wheel - number 3 - was completed today. Unlike the test for the primary wheels, which is performed every three months, the test for the backup wheel is performed every six months. The results were unchanged from those obtained in January 2006 and showed no significant change since early 2004. After the Monopropellant Tank Assembly recharge performed in April of this year, ACS and the Navigation team noticed that the ACS Flight Software (FSW) determination of delta V was always a factor of 1.10 to 1.16 larger than that of their Navigation counterparts. A review of the pre-launch ground based thruster test data indicated that at a feed pressure of 400 psia, the thrusters' tail off time constant is 48.6+or-4.4 msec. ACS FSW had a thruster tail-off time constant of 65 msec based on the pre-recharge pressures. A revised tail off time constant of 43 msec instead of 65 msec could best explain the 1.10 to 1.16-discrepancy factor. To correct the problem, the spacecraft team uplinked the revised value to the FSW today. Saturday, June 3 (DOY 153): The last activity to be performed for S20 was an end of sequence Reaction Wheel Assembly (RWA) bias. The S21 background sequence began execution on June 3 at 2006-154T02:39:00. It will run for about 44 days and will conclude on July 17. The DSN will be supporting Cassini for 48 tracks over three complexes. Nearly 40% of these tracks will be over 70 meter antennas. The sequence contains the Titan 15 targeted flyby, four Orbit Trim Maneuvers (OTM) numbers 63-66, one live update of Hyperion and Enceladus for the Ultraviolet Imaging Spectrograph (UVIS), Imaging Science Subsystem (ISS) and Composite Infrared Spectrometer (CIRS), a ring plane crossing, one each Sun and Earth occultations by Titan, and a dust hazard for 12 minutes on June 30. Watch for the team to close the main engine cover again for this last event. The S21 background sequence began with a standard turn to Earth to downlink data. The first science activity in S21 was a UVIS observation looking for Saturn Aurorae. This was followed by the Cassini Plasma Spectrometer (CAPS) taking control of spacecraft pointing, placing it in a unique orientation to support the Magnetospheric and Plasma Science (MAPS) instruments' study of the structure and dynamics of Saturn's Magnetotail at low latitudes and moderate distances downstream. CAPS also performed a series of spacecraft rolls to allow full spatial coverage for the MAPS instruments. Monday, June 5 (DOY 156): The Cosmic Dust Analyzer (CDA) instrument team successfully uploaded their new version 10.4 FSW to the spacecraft today. FSW checkout is scheduled for June 13. Optical Navigation (Opnav) images were scheduled for acquisition today. The Navigation team using the ISS cameras took images of Saturn's moons against the background star field to help determine the spacecraft trajectory as well as the orbits of the satellites. After the Opnavs, UVIS searched for Saturn Aurorae. The ISS team took a series of images of a unique geometric event, the transit of one Saturnian moon, Telesto, across another moon, Rhea. CAPS then became the prime instrument and continued the Saturn Magnetotail campaign. The day ended with another series of Opnav images. Tuesday, June 6 (DOY 157): The Integrated Test Laboratory concluded a test today of CDS partition 5 playback of Ion and Neutral Mass Spectrometer (INMS) and Magnetometer Subsystem data during the T16 flyby. The final test report is still pending but so far nothing anomalous has been reported. At the end of May, a situation arose where it looked like one or more activities during the S22, Rev 27, Saturn segment might have to be sacrificed. The issue had to do with spending about six hours in the region of less than 300 RPM for the reaction wheels between DOY 227-229. Uplink Operations, Science Planning, Spacecraft Operations and the scientists working with various instrument team representatives have been able to reduce significantly the period of concern with the proposal to add RWA biases during the DOY 227 and 229 downlink tracks and change the initial downlink secondary attitude on the DOY 229 track. ACS presented the final proposal to project management today and it was approved without any loss to the scheduled observations. Many thanks to all who were involved with solving this problem! Wednesday, June 7 (DOY 158): Cassini flight team members were awarded several NASA Honor Awards at a ceremony held today at JPL. Group achievement awards went to Radar Instrument Operations and the Radio Science Subsystem teams as well as the Huygens Ground Doppler and Huygens Probe Earth-Detection Team. The Cassini Literacy Program also received an award for its Reading, Writing and Rings literacy program for 1-4th grade students. In addition to the group awards, several individuals received the Exceptional Achievement Medal at the ceremony. Orbit Trim Maneuver (OTM) # 63 was performed today. This apoapse maneuver sets up for the Titan 15 encounter on July 2. This maneuver fulfills the requirement of the FR10B52 propellant line flushing flight rule. The main engine burn began at 5:45 PM PDT. Telemetry immediately after the maneuver showed the burn duration was 12 seconds, giving a delta-V of approximately 1.9 m/s. All subsystems reported nominal performance after the maneuver. A Cassini in-reach talk was given today on the Cassini RADAR Observations of Longitudinal Dunes. The speaker oriented his audience by starting with the types of dunes seen on Earth and the processes that create them. He then moved on to what has been observed so far on Titan. 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/>
