Cassini Significant Events for 02/20/08 - 02/26/08 The most recent spacecraft telemetry was acquired on Tuesday, February 26, from the Goldstone tracking complex. The Cassini spacecraft is in an excellent state of health and all subsystems are 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. Wednesday, February 20 (DOY 051): Non-targeted flybys of Pan, Prometheus, Pandora, and Janus occurred today. Saturn is currently only a few days away from opposition. At that time Saturn and the sun will be on opposite sides of Earth. Because of this, for the next few months viewing of Saturn will be particularly fine. All Saturn Observation Campaign members are planning Saturn viewing opportunities. Contact one and find a Saturn view in your neighborhood: http://soc.jpl.nasa.gov/members.cfm Thursday, February 21 (DOY 052): The AACS reaction wheel (RWA) drag torque compensation limits for the three prime RWAs numbered 1, 2 and 4 were raised today. This activity requires that at the time of the update the spacecraft be operating on thruster control (RCS) instead of wheels. Because of this, the update was performed at the same time the Radio and Plasma Wave Science (RPWS) Whistler observation - also using thrusters - was executing. The limit had been raised once before for RWA-1, in October 2004, as a response to drag torque trends. Recent trends indicated that another patch, for all three prime wheels, was desirable. Friday, February 22 (DOY 053): The Satellite Orbiter Science Team held an Enceladus-3 flyby preview meeting today. At this event the science teams described the observations to be performed on Mar. 12 when Cassini passes by Enceladus at 50 km altitude. Sequence leads for S38 are still maintaining the possibility of a Live Inertial Vector Propagator (IVP) update for Enceladus. The update would only be necessary if Orbit Trim Maneuver 148 were to be cancelled. An open question is, can the process for an update be executed in time? The necessary orbit determination solution would be available on DOY 069, with all analysis and inputs due prior to uplink the next day, and execution of the update beginning two days after that. It's a bit tight. Stay tuned. The first of three ports occurred today as part of the S42 Science Operations Plan process for the proposed extended mission. S42 is the first of 20 sequences that will execute from July of 2008 through June of 2010. On Friday, Feb. 22, Cassini flew by Titan at an altitude of 1000 km, and a speed of 6.3 km/sec. Peak thruster duty cycle was 41%. Duty cycling is a measurement of how often the thrusters fire in order to keep the spacecraft pointed in the correct direction in response to atmospheric induced torques. A 100% duty cycle would mean that the thrusters are firing all the time. For this flyby, the buzz was all about RADAR and the Ultraviolet Imaging Spectrograph (UVIS). T41 was the prime opportunity in the mission for RADAR to observe the Huygens landing site. The landing site, just east of the Adiri bright region, was previously observed during the T8 flyby in October 2005. The new observations at a lower altitude than at T8 will provide sharper imagery and additional topographic information. The RADAR team used a unique "switch-hitter" pointing design, switching from right-looking to left-looking in order to observe the Hotei Arcus region, a possibly cryovolcanic area to the southeast of Xanadu, as well as the Huygens landing site. The Ion and Neutral Mass Spectrometer (INMS) rode along on the RADAR closest approach observations. The RADAR orientation is important for INMS mid-southern latitude coverage of Titan. INMS is also using Titan as a calibration source prior to the upcoming highly anticipated Enceladus flyby. UVIS had some of the best stellar occultation opportunities in the entire prime mission during this flyby, with opportunities to observe both Eta Canis Majoris and Epsilon Canus Majorus as they were occulted by Titan. These observations will help UVIS understand the so-called detached haze, seen in images at most latitudes outside the polar vortex region. UVIS measurements of aerosols are consistent with these pictures, and more coverage will give increased understanding of the transition region between the upper haze and lower atmosphere. Voyager also saw the detached haze, but much deeper in the atmosphere, so the haze has changed significantly at Titan over the last two decades. If Titan's atmosphere has a locked-in seasonal change, the science teams should be able to detect it over the next few years. Monday, February 25 (DOY 056): As part of the Earth and Space Science Colloquium sponsored by the Office of the Chief Scientist & Chief Technologist and the Science Division, a talk was given today in von Karman Auditorium at JPL on "Enceladus: An Active Ice World in the Saturn System." Tidal heat derived from Enceladus' interaction with Saturn is somehow concentrated under the south pole of the moon, and escapes along a series of fractures, which are also the source for huge jets of ice, water vapor, and other gases. These jets create an enormous ring of fine ice dust around Saturn, the E-ring. It even is possible that liquid water exists under the south pole, providing a potential habitat for life. Cassini is about to embark on a series of eight close flybys of Enceladus which will directly sample the dust and gas jets, and will image the active south polar region in unprecedented detail, promising deeper understanding of this remarkable phenomenon. Tuesday, February 26 (DOY 057): Today Radio Science (RSS) concluded the third and began the fourth Operations Readiness Test (ORT) to demonstrate DSN and RSS preparedness to support the Rings Occultation experiment on DOY 062. The Cassini-Huygens Analysis and Results of the Mission (CHARM) teleconference for February addressed the "Results from the Descent Imager/Spectral Radiometer (DISR) Experiment on Huygens." 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/>
