From: Jet Propulsion Laboratory
Posted: Friday, December 12, 2008
The most recent spacecraft telemetry was acquired on Dec. 9 from the Deep Space Network tracking complex at Canberra, Australia. 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" page at: http://saturn.jpl.nasa.gov/operations/present-position.cfm.
Wednesday, Dec. 3 (DOY 338):
A meeting was held today for the S46 Saturn/Tethys Live Inertial Vector Propagator (IVP) update due to execute on DOY 343-345. This will be a tight schedule with the Go/No Go meeting tomorrow, command approval meeting on Friday, uplink of the commands on Saturday, and execution beginning on Monday, Dec. 8.
Thursday, Dec. 4 (DOY 339):
Based on the pointing error predictions, Science Planning (SP) recommended a GO for the live update of the Tethys vector. The pointing error suggested that the Saturn vectors should also be updated but it was not clear from the plots. After reviewing the data, Imaging Science (ISS), the Visual and Infrared Mapping Spectrometer (VIMS) and the Ultraviolet Imaging Spectrograph (UVIS) teams gave their GO for the update of both vectors. The team is proceeding with the generation and review of the sequence file to be uplinked tomorrow.
A procedure review was held today for the propulsion system fuel-side repressurization activity currently planned for early January 2009. On Monday, a week long dry run will begin execution in the Integrated Test Laboratory to confirm that commands perform as expected.
The final integrated S51 sequence segments for orbits 112-115 are due today. They will be delivered in their final form as there is not time for reintegration at a later date. The Science Operations Plan (SOP) implementation process will begin Dec. 9 with instrument teams beginning work on pointing designs for this sequence. In addition, today is also the first delivery port for S50 Spacecraft Activity Sequence Files as part of SOP development.
For science activities, today began with VIMS measurements of Saturn's atmospheric dynamics in the south polar region. This was followed by an ISS led Titan cloud monitoring campaign. The day concluded with a Magnetometer Subsystem (MAG) calibration roll. These calibrations are needed every 15-20 days in regions where field conditions are suitable.
Friday, Dec. 5 (DOY 340):
Sixteen days after its previous flyby, and just over three days after Saturn closest approach, Cassini flew past Titan for the T48 flyby. The spacecraft was traveling at 6.3 km/sec, passing Titan at an altitude of 960 km, latitude of 10.3 degrees S, and with closest approach occurring at 7:44 AM PST. T48 was the twelfth in a series of outbound encounters and the fourth Titan encounter in the Cassini Equinox mission. T48 and T47 were unique flybys with low phase and high resolution opportunities for the imaging instruments.
T48 was the only dayside pass near Titan's equator in the Prime and Equinox Mission tours. For the Ion and Neutral Mass Spectrometer (INMS), this prime observation measured non-reactive neutrals while simultaneously observing the dayside ionosphere. This flyby also gave INMS coverage of the boundary between the outer flank and wake magnetospheric interaction regions. Outbound, INMS collected measurements from closest approach to the ionospheric peak and into the transition from thermal to co-rotating particles.
For RADAR, T48 represented the end of a series of flybys that observed territory that may be cryovolcanic. RADAR had the opportunity to look at part of Tui Regio inbound. Previous VIMS observations suggested that this region might resemble Hotei Arcus, with an anomalous composition and possible cryolava flow morphologies. Near closest approach, RADAR observed the dark dune fields of Shangri-La while riding along on an INMS observation. Synthetic Aperture Radar looked at a possible impact structure feature seen in ISS data in the south mid-latitudes.
The Composite Infrared Spectrometer (CIRS) conducted far-infrared limb composition measurements, and mapped vertical distributions of CO, CH4, and H2O. In addition, CIRS continued its campaign of mapping the planet in the mid and far-infrared to obtain the spatial and temporal variation of temperature as well as to measure the more abundant hydrocarbon and nitrile molecules. These provide information on possible seasonal changes in weather, climate, and chemistry.
ISS collected global and regional mosaics of Titan's leading hemisphere, including a view of Hotei Arcus in its entirety, as well as southern Xanadu and the western reaches of Tsegihi.
The Magnetospheric Imaging Instrument (MIMI) measured the Titan exosphere and magnetosphere interaction by imaging with the Energetic Neutral Atom camera. This is a component of the MIMI Ion and Neutral Camera (INCA) that can be used when the sun is not in the INCA field of view.
UVIS had its Far Ultraviolet Occultation slit boresight on the star Epsilon CMa as Titan occulted the star. Over the course of the mission, UVIS stellar occultations will sample about 12 latitudes. This sampling will help constrain photochemistry, dynamics and aerosol microphysical processes in the upper stratosphere and mesosphere.
For links to more information on this flyby, go to http://saturn.jpl.nasa.gov/news/events/titan20081205/index.cfm
Monday, Dec. 8 (DOY 343):
Over the weekend ISS performed nighttime imaging using the narrow angle camera to monitor surface and atmosphere changes, and attempted to see surface color variations and monitor limb hazes.
CIRS slewed across the disk and took mid-IR measurements to obtain information on the thermal structure of Titan's stratosphere. CIRS ended the day and began the Rings segment with an observation of the rings designed to map the thermal emission at a variety of viewing geometries to help understand ring particle properties and ring dynamics.
Science Planning provided plots and analysis for the next live IVP update on DOY 350-353, this time for Saturn and Rhea. Although the pointing error was within margin, the pointing plot indicated that the Rhea vector should be updated. For Saturn vectors, the pointing error suggested an update, but the plots suggested otherwise. Instrument recommendations will be necessary to make the final determination in both cases. The Go/No Go meeting is scheduled for tomorrow, Tuesday, Dec. 9, with command approval on Dec 11, and uplink on Dec. 12.
Tuesday, Dec. 9 (DOY 344):
Orbit Trim Maneuver (OTM) #176 was performed today. This was the cleanup maneuver from the Titan 48 encounter on Dec. 5. The main engine burn began at 1:44 PM PDT. Telemetry immediately after the maneuver showed the burn duration was 18.225 seconds, giving a delta-V of 3.032 m/s. All subsystems reported nominal performance after the maneuver.
Today VIMS performed a ring spoke observation in the infrared. With CIRS then leading the pointing, the optical remote sensing instruments observed the Tethys eclipse and VIMS ended the day with a high-resolution observation of the rings.
Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
// end //