Cassini Significant Events 12/14/06 - 12/20/06

December 22, 2006

(Source: Cassini Project)


The most recent spacecraft telemetry was acquired on Wednesday, Dec. 20, 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 http://saturn.jpl.nasa.gov/operations/present-position.cfm


Due to the holidays coming up, there will be no Significant Events report published next week. The report published the week of Jan. 2 will cover the two-week period from Dec. 21 through Jan. 4, 2007.

Thursday, Dec. 14 (DOY 348):

An image of Titan's mountains as seen by the Visual and Infrared Mapping Spectrometer is Astronomy Picture of the Day today. 

On DOY 348, the Imaging Science Subsystem (ISS) performed a 10-hour long azimuthal scan to analyze ring/gap structure and to search for moonlets. The Composite Infrared Spectrometer (CIRS) also obtained sub-millimeter ring temperature scans. These scans are performed periodically to acquire measurements at a variety of geometries such as solar elevation, spacecraft elevation, phase, and Saturn local time.

Friday, Dec. 15 (DOY 349):

Orbit Trim Maneuver (OTM) # 83 was performed today. This was the cleanup maneuver from the Titan 21 encounter on Dec. 12. The main engine burn began at 5:15AM PDT. Telemetry immediately after the maneuver showed a burn duration of 4.8 seconds, giving a delta-V of 0.77 m/sec. All subsystems reported nominal performance after the maneuver.

Cassini has now begun a period of 16 day orbits around Saturn that will last until June of 2007 with one break, a 24 day orbit at the end of January. After June, the orbit duration varies until the 16-day orbits begin again in December of 2007. For each 16-day orbit, three maneuvers have been planned for execution. The Navigation and Spacecraft teams will be busy for quite a while including on Christmas eve and New Year's eve this month.

The Aftermarket process for the S31 sequence began today. This 5-week process will address proposed changes that require re-integration of the segments contained in the S31 sequence. All proposed science and engineering changes are to be submitted by end of day today. If all of the requested changes do not fit within scope, there will be an assessment meeting with the Project Scientist to scope out these proposed changes on Dec. 19. If necessary, on Tuesday, Jan. 16, a final decision meeting will be held to decide what changes will be made to the S31 plan.

Monday, Dec. 18 (DOY 352):

Recently, a number of tweaks to the prime mission tour trajectory have been under consideration. First was an increase in the altitude of Titan 32. T32 is a near-polar pass whose minimum altitude was selected when the atmosphere model had a falloff in atmospheric density near the poles; that has since proved not to be the case, so the altitude of 950 km was deemed to be too aggressive. Second, the high-phase observations on orbit 28 - imagery from which has graced a number of news items and magazines - discovered a new ring at the orbit of Janus and Epimetheus, and Cassini has one traversal through this region in June of 2007 which needed study, in case we should avoid the region. Third, changes in the geometry of the Iapetus flyby in September of '07 had been requested by the Satellite Orbiter Science Team.

During a project-wide meeting held on Dec. 18, the T32 altitude raise was approved, but the Janus/Epimetheus avoidance and Iapetus tweaks were disapproved. No appreciable decrease in risk was gained by the J/E tweak, and the Iapetus tweak had a high delta-V cost. Furthermore, these two tweaks would have caused significant timing changes and a substantial workload increase to reintegrate a wide range of observations. Note that even though the J/E traversal risk is low, the spacecraft will still be adopting a High Gain Antenna to dust ram orientation to protect the spacecraft from any dust that might be present.

Cassini Outreach has announced the start of the second Cassini Photo Contest. Fifteen images obtained by the orbiter since the first anniversary of Saturn Orbit Insertion have been selected by the science teams, are now available for viewing, and for the public to vote for their favorite. Voting will continue through early February when the winner will be announced. Promotion for this web activity includes a prominent link on nasa.gov. A JPL e-postcard and link from jpl.nasa.gov are also expected. To go directly to the Photo Contest page link to: http://saturn.jpl.nasa.gov/multimedia/poll/index.cfm

The Titan 22 encounter will occur on Thursday, Dec. 28. Outreach has posted the T22 Mission Description containing an overview, information about Titan, science highlights, and the event timeline. The document comes in PDF format, and is 1 MB in size. To download this document link to: http://saturn.jpl.nasa.gov/multimedia/products/pdfs/20061228_titan_mission_description.pdf

Currently in production is a web slide show that shows off some spectacular views of the rings. The page will be called¿"Cassini Rings in the New Year." The page is planned to be released during the holiday period so the next time you see it mentioned in this report it will have been out for a while. So, in between wrapping those packages and snagging "just one more cookie", keep an eye on the Cassini website.

Tuesday, Dec. 19 (DOY 353):

RADAR performed a source scan today to provide an absolute calibration reference for all radiometry observations by observing targets that have been characterized from Earth. This source scan also provided an opportunity to perform some engineering tests and collect calibration data for all of the RADAR modes.

Wednesday, Dec. 20 (DOY 354):

The S27 final sequence approval meeting was held today. Uplink of the Instrument Expanded Block files will begin on Dec. 29 and continue into the new year. Sequence execution begins on Jan. 5, 2007. The sequence leads are still waiting on final DSN allocation negotiations. These should be complete by Dec. 22. After the holidays, the team will work the possibility of a real-time science allocation plan mini-sequence, adding a real-time dual-playback for Titan 23 and Titan 24 closest approach data for RADAR and VIMS.

Orbit Trim Maneuver (OTM) # 84 was performed today. This was an apoapsis maneuver setting up for the Titan 22 encounter on Dec. 28. The main engine burn began at 4:59 AM PDT. Telemetry immediately after the maneuver showed a burn duration of 42.7 seconds, giving a delta-V of 6.8 m/s. All subsystems reported nominal performance after the maneuver.

One of the most active Saturn Observation Campaign members sent in an image of a meteor passing "near" Saturn. To view the image link to http://soc.jpl.nasa.gov/experience/gallery-photo.cfm?id=347