Cassini Significant Events for 03/03/05 - 03/09/05 The most recent spacecraft telemetry was acquired today from the Goldstone tracking station. 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 . Activities this week: Science this week included outer magnetospheric survey observations performed by the entire suite of Magnetospheric and Plasma Science (MAPS) instruments, and a MAPS ring and satellite campaign to investigate the exchange of plasma, neutrals and dust between Saturn's ionosphere, rings, and the icy satellites in the inner magnetosphere. Optical remote sensing activities (ORS) included Visual and Infrared Mapping Spectrometer (VIMS) observations of the E and G Rings, and Imaging Science Subsystem (ISS) satellite orbit determination campaigns, feature tracks of Saturn's winds and clouds, and observations of the transit of Janus across Enceladus and Prometheus. ISS jointly participated with Ultraviolet Imaging Spectrograph (UVIS) to observe Dione, Enceladus, Mimas, Rhea and Tethys. Seven hours of ORS images of Rhea were obtained during a 136000 km flyby along with an F-ring movie and brief imaging of Epimetheus and Iapetus. Thursday, March 3: Uplink Operations sent commands to the spacecraft for a VIMS Fast Housekeeping overlay mini-sequence, Radio and Plasma Wave Science (RPWS) +Z Antenna Calibration, and transfer of VIMS Instrument expanded block files to the solid-state recorder. The targeting results from last week's Orbit Trim Maneuver (OTM)-15 are looking so good that there is a chance that the Navigation team will recommend canceling OTM-16, the Enceladus approach maneuver. The OTM-16 approval meeting is scheduled for Saturday at 1:00 PM Pacific time. Normally the Orbit Determination (OD) solution would not come out till the day before. Instead, Navigation is providing an early OD and pointing plots today. Plots with and without the OTM will be made available tonight for evaluation and feedback by Friday. Right now the plan is to redo the plots using the Friday afternoon OD as well. UPDATE: So far it really looks like a no-brainer. You have to look *very* closely at the Composite InfraRed Spectrometer FP1 images to find any differences between with and without the OTM. We will continue to look at this tomorrow with an updated OD, and also look at a few other observations besides those in the Satellite Orbit Science Team (SOST) segment. Friday, March 4: After receiving the expected OD solution today we re-did the plots. These are pretty much identical to yesterdays and to each other. There is now an 11:00 AM status meeting planned for Saturday where the ORS representatives may call in to check and comment if they are OK with canceling the maneuver. As of now the consensus is to cancel. RPWS performed an 11.5-hour post-probe release antenna calibration today. The S11 Science Operations Plan Update process completed today. The sequence product was delivered to the sequence leads for the start of the Science and Sequence Update Process (SSUP) process on Tuesday. A lightning strike interrupted Cassini tracking from the DSN station #15 in Goldstone, California today. Station 26 was brought up in real-time to provide additional support. Saturday, March 5: Due to the very successful OTM-015, which executed this past week, OTM-016 was determined not to be necessary. Consequently, after reviewing the impacts to pointing for Enceladus and T4, we decided to cancel OTM-016. Ok, so why was all this so important and worth reporting? Pointing and targeting are very tightly controlled on Cassini. The instrument teams plan years in advance on what observations will be taken based on the proximity of the spacecraft to a target, and where we are pointing the spacecraft - and subsequently the instruments - at the time. If we cancel a maneuver, it will only be if there is virtually no change to pointing with, or without the maneuver. Hence the importance of science involvement in this decision. OTM-15 put the spacecraft dead on where it needed to be to obtain the Enceladus observations. So, we cancelled OTM-16 and lightened the workload just a bit for a few folks. Monday, March 7: We are getting ready for the Enceladus targeted flyby. Uplink Operations sent an Ion and Neutral Mass Spectrometer Enceladus Measurement program and a RADAR Enceladus Trigger Update to the spacecraft. Today the SOST hosted an Enceladus preview meeting to discuss science objectives and planned activities. All parties have approved the Planetary Data System Data Product Software Interface Specification for the UVIS instrument. The UVIS archive development milestones are now complete. Tuesday, March 8: Today we performed a Reaction Wheel momentum unload onboard the spacecraft. The S11 Science and Sequence Update Process (SSUP) kicked off today. In ten weeks the process will conclude and the new background sequence will be uplinked to Cassini. A picture of the large crater on Mimas was Astronomy Picture of the Day today. Wednesday, March 9: The Rev 4 Enceladus flyby today was the first targeted flyby of this icy moon. The closest approach distance was 500 km. Inbound, for about 7 hours, optical remote sensing measurements were made to probe the geologic history and composition of the surface of Enceladus, measure surface temperatures, and investigate whether a tenuous atmosphere exists. Ten minutes prior to closest approach, Cassini turned into a "safe spacecraft" attitude as it flew through the E-ring, the particle density of which is highest at the orbit of Enceladus. This was Cassini's first pass through the central region of Saturn's E ring. The E ring is a widely distributed, diffuse ring dominated by very small particles which extend from the orbit of Mimas past Dione, about 3 to 8 Saturn radii, and thousands of kilometers above and below the ring plane. Near today's Enceladus flyby, the spacecraft oriented its High Gain Antenna into the incoming particle direction to protect it from any large material that may be in the centermost section of the E ring. UPDATE: Analysis to see if any large particles struck the antenna is currently underway. No spacecraft effects during this crossing have been observed. After the E-ring crossing, only a crescent of Enceladus was illuminated, allowing for key measurements to characterize any thermal activity and surface temperatures. RADAR performed scatterometry and radiometry measurements to understand ice "cleanliness." Along with the Enceladus flyby, Cassini flew within ~85,000 km of Enceladus' neighbor Tethys, providing the opportunity for optical remote sensing observations of that moon. Wrap up: That's it for this week. 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. 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