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Cassini mission updates
5th December, 2005

Pinpointing Huygens Landing Site
1st November, 2005

Left: composite of the imaging camera and the infrared data. On the right is the synthetic aperature radar image.

The Cassini spacecraft carried the European Space Agency's Huygens probe to Saturn and released it in December 2004. The probe landed on Titan Jan. 14, 2005, acquiring a set of images using the descent imager/spectral radiometer camera as it parachuted to the surface.

As Cassini continued to orbit Saturn, its imaging science subsystem and visual and infrared mapping spectrometer mapped the region where the Huygens probe landed. On Friday, Oct. 28, 2005, Cassini's radar instrument provided the highest resolution orbital data yet of this area.

The two images shown here tell the story. On the left, in color, is a composite of the imaging camera and infrared data (red areas are brighter and blue darker, as seen in infrared). On the right is the synthetic aperture radar image. The Huygens descent images are shown inset on the left image and outlined in yellow on the right. The magenta cross in both images shows the best estimate of the actual Huygens landing site. This is a preliminary result, based on the best information available at the present time.

In the left image, the brighter areas seen by the Huygens camera correspond to the large area depicted in red and yellow. On closer inspection, bright features within the Huygens mosaic seem to correspond to smaller features in the map composed of data from the visual and infrared spectrometer and imaging camera. On the right, the correspondence is less clear. In radar images bright features are usually rougher, so one would not necessarily expect an obvious connection.

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.

Cassini positional information

These images show SIMULATED views from the Cassini spacecraft, from several useful points of view which will vary depending on what's happening in the mission. Click on an image to see a full-screen view. These images are updated as circumstances warrant, at least once a day. These computer-rendered images were generated by David Seal using his Solar System Simulator. To obtain Cassini's position in the sky or detailed orbital elements for Cassini please visit the Solar System Dynamics web site and click on the Ephemerides - "Horizons" link. Follow the instructions provided.

Activities this week:

Tuesday, November 22 (DOY 326):

It's going to be a very busy week on through the Thanksgiving holiday. Today at 9:00 AM, the DOY 330 Live Inertial Vector Propagator (IVP) Kickoff Meeting was held. Then at 2:00 PM the Orbit Trim Maneuver 43 (OTM) cancellation meeting was held. It was decided not to cancel. Finally, at 9:00 PM the OTM-043 approval meeting was held.Radio Science Subsystem (RSS) team members performed a Gravity Operations Readiness Test (ORT) in preparation for Rhea gravity science observations to be executed over the weekend.

Wednesday, November 23, (DOY 327):

The Rhea DOY 330 Live Update was cancelled today at the Go/No Go meeting. Since OTM-043 was not canceled, changes in the trajectory will be negligible.

Orbit trim maneuver #43 (OTM-43) was performed today. The Reaction Control Subsystem burn began at 6:15 am PST. Telemetry immediately after the maneuver showed the burn duration was 63.125 sec, giving a delta-V of approximately 60 mm/s. All subsystems reported nominal performance after the maneuver.

Pandora: A Shepherd Moon of Saturn was Astronomy Picture of the Day today. Cassini passed about 50,000 kilometers from the moon in early September and captured the highest resolution image of Pandora ever taken. Features as small as 300 meters can be discerned on 80-kilometer wide Pandora. Craters on Pandora appear to be covered over by some sort of material, providing a much smoother appearance than sponge-like Hyperion. Pandora is of interest because, along with its companion moon Prometheus, it helps shepherd the particles of Saturn's F ring.

Thursday, November 24 (DOY 328): Thanksgiving Day

It's Thanksgiving Day and all is well with the spacecraft� and a handful of people who needed to come in to support commanding today. Flying a spacecraft is a 24-7 operation! Uplink Operations, Mission Support and Services Office Personnel, and team personnel from RADAR, the Magnetometer Subsystem (MAG), and the Cosmic Dust Analyzer (CDA) supported the uplink of commands for a RADAR Instrument Expanded Block trigger for Rhea, a change of MAG housekeeping mode, a CDA setup mini-sequence, CDA commands to reset and reload, and finally, commands to update downlink telemetry modes for the DSS-24 and DSS-15 passes on DOY 334. The uplink of telemetry modes is due to the late "coming on line" of DSS-15. The details of what Cassini is doing to work around the DSS-15 situation were reported last week.

Friday, November 25 (DOY 329):

MUSES-C requested additional Goldstone coverage to support their asteroid touchdown. The Cassini Program was contacted by the DSN schedulers regarding this situation. After discussion it was determined that RSS would be willing to release the end of the DSS-26 Cassini track without significant impact to the RSS ORT or Gravity Science experiments underway
today. This worked for all parties involved.

Saturday, November 26 (DOY 330):

On November 26, Cassini made its only targeted flyby of Rhea in the prime mission. During this, one of the best icy satellite encounters of the tour, the Magnetospheric and Plasma Science instruments performed observations during the almost diametric wake crossing at 500 km altitude, with excellent and stable ride-along during the RSS observations. This flyby was ideal for studying Rhea's interaction with the magnetosphere and for measuring the composition of material sputtered off the surface. The Optical Remote Sensing instruments performed global mapping and global color observations at spatial resolutions up to 270 m/pxl. Near closest approach, while the spacecraft was Earth pointed for the gravity experiment, the cameras took a few images that might reach spatial resolutions better than 20 m/pxl. RADAR took scatterometry data of four quadrants of Rhea as well as radiometry raster scans centered on the target.

Cassini Radio Science conducted a Rhea Gravity Observation on Saturday and Sunday, November 26 and 27. This was the last planned RSS icy satellite gravity observation in the tour and a very important observation for RSS gravity science. Only Titan and Saturn gravity observations remain.

Sunday, November 27, (DOY 331):

Non-targeted flybys of Enceladus and Helene occurred today. Observations included Enceladus color photometry/polarization and geyser/plume search, transits of Enceladus across Calypso, Epimetheus across Janus, and Tethys across Enceladus, as well as other Tethys observations, and a Mimas spectrophotometry campaign.

OTM-044 was successfully performed today. The RCS burn began at 9:27 PM PST. Telemetry obtained immediately after the maneuver showed the burn duration was 262.75 sec, giving a delta-V of about 237 mm/s. All subsystems reported nominal performance after the OTM.

Tuesday, November 29 (DOY 333):

Soon the project will be coming to a decision about what Titan altitudes to fly for the remainder of the prime mission. All of the relevant data has been made available for any review or analyses the teams might wish to conduct. A Mission Planning forum was held today to discuss the Titan altitude profile for the remaining flybys. Since time is growing short on this issue, now is the time for the science teams to perform studies and ask questions. It is planned that the altitude profile will be selected this week, after which point it will be too late to argue for higher or lower altitudes.

Wednesday, November 30 (DOY 334):

CDA performed a scheduled decontamination today.

At 10 a.m. EST Wednesday, the European Space Agency (ESA) presented the latest Huygens probe and Mars Express orbiter results during back-to-back briefings from the agency's Paris headquarters.

Mission Planning presented statistics on low Titan flyby altitude tumbling densities and model uncertainties to the Project today. Safe altitudes were shown as a function of risk factor. After discussion, the Program Manager chose to use a risk factor around 5%. Specific altitudes were then modified by rounding inbound flybys up and by rounding outbound flybys down. In two
special cases science requested and was granted an additional 5 or 10 km lower. For the two flybys with optional orientations, science requested to choose the higher altitude to preserve science options. Mission Planning will present a final product of approved altitudes to the Navigation Team this week.

Wrap up:

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.

Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest press releases and images.