Cassini Significant Events 01/31/07 - 02/06/07

February 8, 2007

(Source: Cassini Project)

The most recent spacecraft telemetry was acquired on Tuesday, February 6, 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 at .

Wednesday, January 31 (DOY 031):

An instrument flight software update delivery coordination meeting was held today for Composite Infrared Spectrometer (CIRS) version 5.0. The update included four new CIRS internal commands, added ability to pre-filter raw data, and added additional items to housekeeping telemetry.

A time-lapse movie of Cassini crossing Saturn's ring plane is Astronomy Picture of the Day today.

Science observations on Wednesday included Ultraviolet Imaging Spectrograph (UVIS) observations of the occultation of a star by Enceladus. Saturn's moons Tethys and Rhea were imaged for optical navigation use.

Thursday, February 1 (DOY 032):

The final plenary session of the Cassini Project Science Group (PSG) meeting concluded at 4:00 today. The attending group of scientists and flight team members were able to narrow the selection of a tour extension trajectory down to three candidates. Those three were then passed off to members of the PSG Executive Session to make the final selection. Tour PF6h9 was the selected tour. On Feb. 15, the Program will present a proposal to NASA for a continuation of the Cassini mission beyond its current nominal plan of four years. The presentation will include an overview of the selected tour and science rational for an extended mission.

The Media Relations Office has issued an image advisory on an infrared image taken by the Visual and Infrared Mapping Spectrometer (VIMS). On Dec. 29, 2006, VIMS imaged a giant cloud on Titan half the size of the United States. Scientific models had predicted this cloud system, but it had never been imaged in such detail before. The same cloud system seen on Dec. 29 was still there two weeks later during a Jan. 13, 2007, flyby, even though observing conditions were slightly less favorable than in December. The cloud may be responsible for the material that fills the lakes discovered last year by the RADAR instrument. For the full story and associated images link to:

Two different types of observations today focused on the high latitudes of Saturn. The Imaging Science Subsystem (ISS) used photopolarimetry to study the physical properties of particulate matter in Saturn's atmosphere by measuring the intensity and polarization at different wavelengths. VIMS made simultaneous observations.

Periapsis of orbit 38 was at 2007-032T09:57:52 at a distance of 15.6 Rs. The Radio and Plasma Wave Science (RPWS) instrument took advantage of the proximity at periapsis to observe Saturn Kilometric Radiation (SKR) at millisecond resolution to characterize its temporal structure.

Outbound from periapsis, ISS, CIRS, and VIMS began a campaign to try to catch a spoke forming on the rings near the morning shadow edge at a ring radius of 110,000 km.

Friday, February 2 (DOY 033):

A non-targeted flyby of Titan occurred today. For this flyby RADAR turned its attention toward the satellite for radiometer data of the southern latitudes.

Optical navigation images were taken today of Rhea and Enceladus.

Saturday will provide an opportunity to observe Dione at low phase and even at zero-phase. In this geometry, since phase angle measures the angle from Sun to satellite to Cassini, there are no shadows on the surface. As the phase approaches zero, the observing instruments see an opposition surge in which the target brightens far more than would normally be expected.

Also on Saturday, ISS will observe a transit of Saturn's moon Mimas in front of the much smaller Helene. The exact time when the satellites are aligned in the instrument's field of view helps to refine determination of their orbits.

Sunday, February 4 (DOY 035):

Early in the day, Cassini crossed through the ring plane from south to north at approximately 20Rs from Saturn. The MAPS (Magnetosphere And Plasma Science) instruments used this crossing to measure the vertical profile of the Titan torus. The opportunity will be repeated at this distance but in a descending crossing on the 16th of February.

Saturn with all of its rings and its satellites Dione and Telesto were captured together in a single image. Tethys, Mimas, and Epimetheus starred in another image with the rings. Mimas was the object of an optical navigation image.

Monday, February 5 (DOY 036):

The A8.7.5 Attitude and Articulation Control Subsystem (AACS) flight software (FSW) patch has been declared to be a success. While the FSW upload procedures would occur over a week of prime and backup passes, the A8.7.5 parameter updates involved months of planning, testing and reviews. Many hard hours of work and effort were invested to mitigate any risk involved in patching the FSW, which now resides on the Solid State Recorders (SSR)s and AACS Flight Computers (AFC)s. This load changed parameters and vectors only. There were no logic changes. Changes included:
Default thruster magnitude updates,
Default secondary safing vector pair for window Feb. - Dec., 2007,
IRU-A scale factor updates,
Phantom momentum-related FP parameter updates.

Still on the slate to wrap up events for this update is the first in-flight IRU-A gyro calibration with the new scale factor values on Feb. 27. The FSW normalization involving the copying of AACS FSW A8.7.5 from the non-default to default partitions of the SSR is scheduled to occur on March 4, 2007. The next AACS FSW update, version A8.7.6, is coming up in January, 2008.

Tuesday, February 6 (DOY 037):

Dione was the first target of observations today with CIRS observing in the infrared and UVIS in the ultraviolet. An image was taken of each of Enceladus, Epimetheus, Atlas, Prometheus, and Pandora for orbit determination purposes. Attention then turned from satellites to rings. VIMS made a 3x1 mosaic of each ansa of the rings. UVIS observed an occultation of the star Psi Cen by the rings.

Cassini outreach presented an overview of "Reading, Writing & Rings" at JPL to a group of 60 after school educators from disadvantaged schools participating in the Collaborative After School Project (CASP). The Project is dedicated to fostering developmentally oriented learning experiences for children and youth during the after school hours. For more information link to:

The sequence leads for S28 have reported that after the last merge of input products, the sequence size was over the memory limit by 4128 words. A time to split the sequence into Parts A and B has been selected on DOY 074. Requests have been sent to all participants to let the leads know by Feb. 7 if there are any concerns or issues with the selected time. The uplink of S28 files to the spacecraft begins next week. S28 begins execution on Feb. 17.

A kick-off meeting has been scheduled for Thursday for a live update for VIMS and RADAR observations of Hyperion. Based on the post OTM-93 trajectory, the Hyperion errors are much smaller than last week but still substantial. An update currently seems wise.

The sequence leads for the S30 Science Operations Plan Update process received the products for the official input port today. The products will now be merged, sent to the Spacecraft team for review, then posted to the official file repository for review.

A delivery coordination meeting was held today for Cassini Radio Science Predicts software version 3.0. The purpose of the program PREDICTS is to predict the radio frequencies to be received by the Radio Science Receiver (RSR) as a function of time. The Radio Science System Group at JPL uses this program for receiving data during operations pertaining to Radio Science experiments. The Cassini Radio Science Operations Team uses it for specific Cassini operations pertaining to Cassini Radio Science experiments.

Now that the project has selected a tour to fly for extended mission, the question arises, what next? This was the topic discussed at the Mission Planning Forum this week. Specific items included receipt of tweak requests, how much time should be allocated to the requests, review, and final analysis, TOST jumpstart results, and generation of the reference trajectory for the extended mission. A draft schedule was presented with dates for these and other milestones.

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