Cassini Significant Events — 11/02/05 – 11/09/05

Cassini Significant Events -- 11/02/05 - 11/09/05

November 11, 2005

(Source: Cassini Project)

Wednesday, November 2 (DOY 306)

A Cassini image of the slow dancing moons Epimetheus and Janus, along with Saturn's rings, is Astronomy Picture of the Day today.

The S19 Science Operations Plan Update kickoff meeting was held today. The process runs for five weeks and will conclude on December 9.
The Program has made the decision to delete three apoapsis Orbit Trim Maneuvers (OTM) in advance: OTM-48 on January 2, 2006, OTM-54 on March 5, 2006, OTM-60 on May 7, 2006.
The decision to cancel was made because there were only three DSN tracks between the post-encounter cleanup and apoapsis maneuvers, delivery errors did not improve after the apoapsis maneuver, and the maneuvers would be difficult to cancel in real time. The delta-V cost is about 0.8 m/sec. The early deletion, as opposed to real time cancellation, allows for the elimination of the meetings, analysis, and preparation associated with the normal process of deciding to cancel or perform these maneuvers. Most OTMs are not candidates for such early cancellation because they either have a sizeable deterministic component or a significant probability of being required in order to meet mission requirements.

Members of the RADAR instrument team gave a Cassini internal presentation on RADAR science results.

Thursday, November 3 (DOY 307):
This week on board the spacecraft several of the instruments turned their attention to Iapetus. The Imaging Science Subsystem (ISS) performed a global map, obtaining geologic, geographic, and topographic data, the Ultraviolet Imaging Spectrograph (UVIS) measured the UV albedo across various longitudes and phase angles, and the Composite Infrared Spectrometer (CIRS) performed observations with high spectral resolution integration for composition and for phase angle coverage. These were all relatively distant observations leading up to next week's closest approach point of around 417,000 km. In addition to their own Iapetus observations, the Visual and Infrared Mapping Spectrometer (VIMS) observed the E ring from 30-40 Saturn radii in order to build up spectra at different phase angles, and the Magnetospheric and Plasma Science instruments were able to observe the dawn-side magnetospheric boundaries over a range of radial distances, as well as obtain solar wind data.

Friday, November 4 (DOY 308):
A command approval meeting was held today for S16 Instrument Expanded Block (IEB) loads for ISS, VIMS, CIRS, UVIS, the Cassini Plasma Spectrometer, and optical navigation. Uplink of these files to the spacecraft will begin on Tuesday, November 8, at 1:00 AM PST.

The Science Allocation Panel (SAP) meeting held today was not the usual meeting for sponge bit allocation. Instead, due to a change from a 70 meter to a 34 meter DSN station for the downlink on 2006-069, the meeting was used to determine how to reduce data volume by 335 Mb on that pass, the last of the S18 sequence.

The Solid State Power Switch (SSPS) on line 1 of Reaction Wheel Assembly-4 (RWA) tripped off unexpectedly today 51 weeks after the last such trip on November 11, 2004. That time it was line 2 of RWA-1. These SSPS trips have been seen before and are believed to be caused by Galactic Cosmic Rays (GCR). So far in the mission there have been 13 such trips, and they are predicted to occur at a rate of about two per year. There was no impact to spacecraft performance, as there are two SSPSs and power lines per RWA, but each line is capable of carrying the entire load. The tripped switch was brought back online by stopping the downlink roll, transitioning to Reaction Control System (RCS) control, thereby turning off all three reaction wheels, biasing the wheels, and going back to RWA control. About 35 minutes of the roll for science data acquisition was lost, but there was no interruption of the downlink telemetry. The spacecraft is operating normally following this activity.

Monday, November 7 (DOY 311):

The S16 Final Sequence approval meeting was held today. S16 will begin execution on board the spacecraft on Saturday, November 12.

The Project has selected a Monopropellant Tank Assembly (MTA) recharge date of April 10, 2006. This recharge date allows the thrusters to be at optimal pressure to provide control authority for the planned 950 km Titan flybys starting with T-16 on July 22, 2006. Calculations showed that the predicted tank pressure after repressurization is about 406 psia. The hardware is designed and qualified to operate properly at 420 psia.

Tuesday, November 8 (DOY 312):
Uplink to the spacecraft of six IEBs began today. The activity is scheduled to complete tomorrow. Additional commanding included a Magnetospheric Imaging Instrument automated sequence processor command, and a command to clear the CDS error logs.

Wednesday, November 9 (DOY 313):
Commanding continued today with uplink of the remaining IEB files, the S16 background sequence, the S15 end of sequence real time RWA bias, and a RADAR IEB trigger.

A Tour Science talk was given today on recent Cosmic Dust Analyzer science results concerning Enceladus and the E-ring.

A delivery coordination meeting was held today for the Spacecraft Operations Office tool Flight Software Development System (FSDS) version 2.2. FSDS is a simulation environment for the Cassini ACS subsystem. It provides the user with a command line interface for visibility into the spacecraft simulation, the flight software and the ground interface. Users can retrieve and set variables in the hardware, peek and poke global variables in the flight software, and check telemetry values.

Wrap up:
The most recent spacecraft telemetry was acquired Wednesday, November 9, from the Goldstone tracking complex. The Cassini spacecraft is in an excellent state of health and all subsystems are operating normally. Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest press releases and images.