NASA Cassini Significant Events for 11/16/06 – 11/21/06
The most recent spacecraft telemetry was acquired Tuesday, November 21, from the Madrid tracking stations. The Cassini spacecraft is in an excellent state of health and is operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the “Present Position” web page located at /operations/present-position.cfm .
Thursday, November 16 (DOY 320):
Due to the Thanksgiving Holiday, the Significant Events Report (SigEs) will cover a 6-day period this week, and will cover an 8-day period next week.
The DOY 324-326 Live Inertial Vector Propagator update files were sent up to the spacecraft today along with a RADAR mini-sequence to update the RADAR Instrument Expanded Block (IEB) for the Dione observation on Tuesday. The Radio Science Subsystem performed an antenna boresite calibration today.
Friday, November 17 (DOY 321):
Beginning today and continuing until Thursday, November 23, files in support of the S26 sequence will be uplinked to the spacecraft. Today, IEBs for Imaging Science Subsystem (ISS), Visual and Infrared Mapping Spectrometer (VIMS), Ion and Neutral Mass Spectrometer (INMS), Ultraviolet Imaging Spectrometer (UVIS), and Cassini Plasma Spectrometer (CAPS) were sent. Tomorrow additional INMS, Composite Infrared Spectrometer (CIRS), and Optical Navigation IEBs will go up. The background sequence will be uplinked on Tuesday, November 21, and will begin execution on Friday, November 24.
Monday, November 20 (DOY 324):
At the weekly Project Staff meeting it was announced that Orbit Trim Maneuver (OTM) 81 would execute over the backup window on November 27, instead of during the primary window on November 26. The current Titan 20 to Titan 21 transfer consists of four orbits, each with a duration of 12 days. This is the shortest orbit period to date in the Cassini tour. OTM-80, the first of three OTMs supporting the T20-T21 transfer, left ~70 km to be corrected in the T21 target B-plane. When the upcoming OTM-81 was computed at the backup window, it turned out to be only ~0.2 m/s, less than a third of the ~0.75 m/s at the prime window.
In the past, the backup location occasionally resulted in a slightly smaller delta-v than the prime location, but never has there been such a large reduction. It turns out that between the prime and backup locations for OTM-081, there is a peculiar singularity not observed before. While the geometry is still being analyzed, the situation presented a rather unique trade off – a main engine burn at the prime location which retains a ‘backup’ location vs. a smaller and more accurate reaction control subsystem burn which increases the likelihood of being able to cancel the T21 approach maneuver at OTM-82. Cancellation of an approach maneuver, if possible, always has merit in that there is less disturbance to the spacecraft on its final approach to a targeted flyby and thus to the associated science activities.
Members of the Navigation team made a presentation to the Program manager on November 15. A decision was reached to perform OTM-81 at its backup location, with OTM-82 becoming the backup to OTM-81. OTM-82 is nominally zero if OTM-81 is performed as planned, but otherwise will go to 0.3 m/sec.
Tuesday, November 21 (DOY 325):
A non-targeted encounter of Dione occurred today at an altitude of 74,783 km. Observations of this satellite were made by VIMS, CIRS, UVIS and RADAR. After the flyby, CIRS conducted a thermal and sub-millimeter mapping campaign of the rings, VIMS took a complete hi-res radial scan of the unlit face of the A, B and C rings at low phase angle, and UVIS observed a stellar occultation.
The Magnetospheric and Plasma Science (MAPS) instruments conducted several campaigns this week. Observations were made of the auroral magnetosphere – the acceleration region – and Saturn Kilometric Radiation (SKR) source regions, and measurements were made of the vertical structure and dynamics of the inner magnetosphere on orbits nearly tangent to L-shells at a variety of local times and L-shells. L-shell means basically the radial distance from Saturn. Here is a definition: a region defined by where magnetic field lines cross Saturn’s magnetic equator. For example: an L-shell equal to 5 roughly represents the set of field lines that cross the magnetic equator at 5 Saturnian radii from Saturn. A satellite’s L-shell represents the set of field lines that cross the equator near the satellite’s orbit.