Cassini Significant Events for 03/16/06 - 03/22/06 The most recent spacecraft telemetry was acquired Wednesday, March 22, 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, March 16 (DOY 075) In the Meridian room of Dunsink Observatory in Castleknock, Ireland, a Saturn Observation Campaign (SOC) member hosted 55 people for a presentation about JPL's Spirit of Exploration and the stunning images from the Cassini Mission. Unfortunately the evening's Saturn-gazing had to be cancelled due to appalling weather. Thirty-five 2nd grade elementary school students, their parents, and teachers gathered in Grossrinderfeld, Germany to view Saturn, the Orion nebula and the Pleiades star cluster. Kids and parents alike said a big "wow" after looking for the first time at Saturn and its clearly visible moons. Friday, March 17 (DOY 076): Uplink operations sent commands to the spacecraft today for the DOY 080 Rhea Live Inertial Vector Propagator (IVP) update, and RADAR Instrument Expanded Block Update mini-sequence for Rhea. All files have been verified onboard the spacecraft. Saturday, March 18 (DOY 077): On March 18 the Cassini spacecraft conducted the 13th targeted flyby of Saturn's moon Titan. With a closest approach altitude of 1,951 km, this flyby provided the first Cassini tour opportunity for Radio Science (RSS) to observe Titan's ionosphere and neutral atmosphere using radio occultation, and Titan's surface using bistatic scattering. The radio occultation is the second ever of Titan, the first being a sole Voyager occultation in 1980. During approach to Titan, the Cassini high gain antenna boresight was pointed to illuminate regions of Titan's surface for which mirror-like reflections of the incident radio signals can be observed at the DSN ground receiving stations. The strength and polarization properties of the reflected signals, if detectable, provide important information about the physical nature of the surface region probed, as well as the surface roughness. Radio Science has reported that the S- and X-band data is of exceptionally high quality. Both the large and small-scale structure of the atmosphere at the two observation latitudes are well captured in the data. The data is consistent among the multiple stations observing at the same time, clearly indicating that the structure observed is real and not noise. The details of the small-scale structure appear to be different for the ingress and egress sides. Despite spacecraft pointing being controlled by thrusters and poor weather at both Goldstone and Madrid at the time, the Ka-band amplitude stability appears to remain surprisingly good throughout the approximately one hour observation period. All indications are that T12 was remarkably successful, the first Titan occultation in 25 years, the first at three wavelengths, and the first Titan bistatic experiment as well. Tuesday, March 21 (DOY 080): Orbit trim maneuver (OTM) #56 was performed today. This is the cleanup maneuver from the Titan 12 encounter on March 18. The main engine burn began at 9:30 PM PST. A "quick look" immediately after the maneuver showed the main engine burn duration was 2.71 seconds, imparting a delta-V of approximately 0.44 m/s. All subsystems reported nominal performance after the maneuver. This week Cassini had one of the closest Rhea flybys in the tour. Optical remote sensing observations, along with a RADAR block, were used to probe the surface composition and geologic history of the largest icy satellite orbiting within the magnetosphere and E-ring environment. In particular, the Ultraviolet Imaging Spectrograph (UVIS) conducted compositional investigations of Rhea's surface and the "near-Rhea" environment to search for a tenuous atmosphere. The Cosmic Dust Analyzer (CDA) continued with its search for Saturnian dust stream particles. In addition to its icy satellite high phase campaign, the Imaging Science Subsystem (ISS) observed the sub-Saturn hemisphere of Rhea at the best resolution of the prime mission, as well as part of the surface in "Saturn-shine". Today the Navigation Team released reference trajectory 060323 for Project use. The new trajectory was designed to raise the minimum Titan flyby altitude from 950 km, and will be used in the Aftermarket Process for sequence development of S23. Wednesday, March 22 (DOY 078): The final system mode end-to-end test for the Monopropellant Tank Assembly (MTA) recharge and ACS flight software A8.7.4 uplink activities began today and will conclude on Thursday. The recharge brings the thrusters up to nominal thrust levels to provide control authority for the planned lower altitude Titan flybys, starting with T-16 on July 22, 2006. Reaction Wheel Assembly (RWA) #1 exhibited three drag torque spikes so far in 2006 -- on February 8, and, more recently, March 15 and 16. Before this year, the last drag torque spike on RWA-1 occurred in 2001. RWA-1 has been troublesome in the past, exhibiting excessive drag torque in 2004, although a friction test on January 27, 2006 showed a positive trend since early 2004. The ACS team is keeping an eye on this. The S21 Science Operations Plan update Project Briefing was held today. S21 now moves on to the final sequence development process that will kick off Tuesday of next week. A delivery coordination meeting was held for Navigation tool set T2.3. This is an incremental delivery of multi-mission Navigation software. A gorgeous picture of Enceladus hovering just above the rings was Astronomy Picture of the Day today. Wrap up: Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest press releases and images. Do you want to know where Saturn viewing might be happening in your area? We have over 350 members of the Saturn Observation Campaign in 45 states and 49 countries around the world. Contact one of the SOC members in your state to ask when and where you can see Saturn. http://soc.jpl.nasa.gov/members.cfm 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/>
