Cassini Significant Events 10/26/06 - 11/01/06

November 3, 2006

(Source: Cassini Project)


The most recent spacecraft telemetry was acquired on Wednesday, Nov. 1, 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 .


Thursday, Oct. 26 (DOY 299):

The Spacecraft Operations Office (SCO) Solid State Power Switch (SSPS) Trip Working Group held their first meeting today. Options are being examined for possibly increasing the system fault protection persistence filter values for two radio frequency subsystem components. The group also plans to review the instrument and subsystem SSPS trip fault protection settings. The rationale for changing the persistence filters is to avoid spacecraft safing and unnecessary hardware swaps for a simple SSPS trip in the deep space transponder or traveling wave tube amplifier.

Friday, Oct. 27 (DOY 300):

Members of the Attitude and Articulation Control Subsystem (AACS) have developed an automated reaction wheel assembly drag spike tracking tool. The tool will track spikes greater than 5 milli-Newton-meters (mNm) in magnitude, and persisting longer than 60 seconds. It will exclude those occurring immediately after zero crossings that occur as a result of discontinuities near zero rpm, and those occurring when the spacecraft rate is greater than 0.1 mrad/second due to uncertainties during acceleration and deceleration phases.

A kick off meeting was held today for a Live Inertial Vector Propagator (IVP) update for DOY 311-315. The Navigation team provided a special orbit determination (OD) solution based on the Titan 20 flyby for this event. Analysis of this update by Science and Operations teams indicated that the update was necessary. Members of the RADAR team also reported that based on the new OD, an updated Enceladus-Rev 32 instrument expanded block would be needed for the RADAR instrument. The necessary files have been received by the sequence leads and will be approved for uplink on Nov. 2.

Members of CDA have informed the S25 leads that they wish to uplink a patch to instrument flight software. The patch has been approved by project management and will be uplinked mid-November.


Monday, Oct. 30 (DOY 303):

A post Titan 20 Titan Atmosphere Model Working Group (TAMWG) meeting was held today. For T-20 it was reported that the AACS duty cycle was higher than from just atmospheric torque compensation. This was due to turns for the Visual and Infrared Mapping Spectrometer (VIMS) observations shortly after Titan closest approach (CA). The density at 1030 km was estimated to be 6.7E-10 kg/m3. The next TAMWG meeting is scheduled for December 20, after the Titan 21 flyby. At that time, the TAMWG will recommend an updated density model. AACS hopes to have the results of their T20 accelerometer data analysis finished by that date.

Two future flybys will also receive additional scrutiny. Since Titan 27 has a lot of turns near closest approach, and the turn design has changed since the tumble density was last calculated, AACS will release a new T27 tumble density estimate on Friday, Nov. 3. In addition the altitude of the Titan 32b flyby was selected using an old density model and now has a predicted duty cycle of 80%. The Titan Orbiter Science Team is expected to choose between T32a and T32b in early December.

All teams participating in S28 submitted their preliminary input products as part of the Science Operations Plan Update Process. Final inputs are due next week with a program briefing scheduled for Nov. 20.


Tuesday, Oct. 31 (DOY 304):

The Project Scientist has made a decision on the science trade between ISS Enceladus and CDA E-ring observations to occur during S29. The two plans proposed by the teams concerned were named "Carte Blanche" and "Plan B." Both offered the prospect of achieving excellent scientific results. Carte Blanche would mainly carry out optical remote sensing (ORS) observations, whereas Plan B offers many instruments some opportunities.

In resolving situations of this kind, the Project Scientist must consider several criteria in deciding which science will take priority. The criteria used for resolving this contention were:

1) In order to select Carte Blanche, the incremental scientific value of the results achieved by Carte Blanche over what we know now and what we will know if Plan B is executed must clearly exceed the scientific value of the CDA data to be obtained in Plan B.
2) A demonstration that the additional ORS observations gained under Carte Blanche can only be obtained in S29.

FINDINGS:

1) The CDA in situ measurements to be made in Plan B are directly related to achieving Cassini-Huygens objectives originating in the NASA and European Space Agency Announcements of Opportunity. The desire for these measurements was the reason for selecting the CDA instrument. Furthermore, this characterization of the E-ring by CDA will be valuable as a boundary condition for constraining models of Enceladus' plume activity and ring models. The S29 opportunity is unique in the primary mission and is not foreseen as occurring in an extended mission.

2) Carte Blanche offers some geometric opportunities which are important for the interpretation of the grain size and other properties of Enceladus' plume particles. It may afford the best opportunity for sorting out the exact locations of some plume vents. Other opportunities for approximately similar observations exist in the primary mission and are foreseeable in an extended mission. However, it is problematical that all the observations to be obtained under Carte Blanche could be done later.

JUDGEMENT:

Carte Blanche is good but it is not as fundamentally important as Plan B. The Cassini-Huygens Project will adopt Plan B for S29.

Wednesday, Nov. 01 (DOY 305):

Orbit 31 periapse occurred this week. Science opportunities for this event included one of the first Magnetospheric and Plasma Science (MAPS) instruments studies of the auroral region in which the spacecraft crosses magnetic fields at high latitudes. The MAPS instruments also carried out a vertical profile of the inner magnetosphere during this periapse, taking advantage of Cassini's trajectory from south to north at a relatively constant distance from the planet.





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