Cassini Significant Events for 08/29/07 - 09/04/07

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Cassini Significant Events 
for 08/29/07 - 09/04/07

The most recent spacecraft telemetry was acquired on Tuesday, September 4,
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 located at
http://saturn.jpl.nasa.gov/operations/present-position.cfm.

Wednesday, August 29 (DOY 241):

Cassini passed Tethys today for a non-targeted flyby at  a distance of
55,499 km.  The Optical Remote Sensing (ORS) instruments performed imaging
and mapping activities, and obtained measurements of the ultraviolet albedo
across both longitude and phase space.  Additional science activities
included an F-Ring rotation movie and raster scans of the north and south
regions of Saturn  by the Composite Infrared Spectrometer (CIRS), and
scatterometry and radiometry observations of Phoebe performed by RADAR.

Thursday, August 30 (DOY 242.):

The day after Tethys, Cassini encountered Rhea during the outbound leg of
orbit 49. Closest approach was 5,737 km at a phase angle of 46 deg. The Rhea
science observations included Imaging Science Subsystem (ISS) mosaics, an
Ultraviolet Imaging Spectrograph (UVIS) map of the surface albedo of Rhea in
UV and limb drifts to determine atmospheric scattering, and CIRS high
spatial resolution mapping. In addition to the ORS observations, the suite
of Magnetospheric and Plasma Science (MAPS) instruments, which includes the
Cassini Plasma Spectrometer (CAPS), Cosmic Dust Analyzer (CDA), Ion and
Neutral Mass Spectrometer (INMS), Magnetometer Subsystem (MAG),
Magnetospheric Imaging Instrument (MIMI), and Radio and Plasma Wave Science
(RPWS), simultaneously performed low-rate magnetospheric surveys.  The live
update commands uplinked to the spacecraft on Aug. 28 were extremely
successful. Very detailed images of a crater of interest have been returned
and the scientists are quite excited.

Using the latest orbit determination (OD) solution, the maneuver team has
been able to show that there is virtually no difference between the
trajectory to Iapetus with or without OTM-126.  Further, the current
prediction is that OTM-126 would be very small and might have to be
cancelled as a result of being below the minimum delta V.  There was no
mission delta V penalty associated with deleting OTM 126.  The current OD
solution has a relatively large uncertainty. The consensus of flight team
members was that even if there were sizeable changes in the OD solutions,
the conclusions relative to the deletion of OTM-126 would not change.
Therefore OTM 126 is now deleted.

Near midnight, Cassini began observations for the Titan T35 targeted
encounter.  Closest approach was at an altitude of 3,326 km, a speed of 6.1
km/sec, outbound from Saturn at a phase angle of 87 degrees. The main engine
cover was reopened just prior to the encounter.  This flyby placed Cassini
on a course to conduct the closest flyby of Iapetus that will be performed
during the entire mission. On Sept. 10, Cassini will come within 1,650
kilometers from the surface of Iapetus.  For more information on the Iapetus
flyby link to:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=771

You may see differences in the date reported for when the T35 flyby
occurred.  Was it the 30th or the 31st?  The answer lies in Spacecraft Event
Time (SCET), which is always stated in GMT at the spacecraft.  Closest
approach for Titan was at 2007-243T05:32:34 SCET.  DOY 243 = August 31.
But, when you convert SCET to Pacific Daylight Time, the time moves earlier
and lands on the 30th.  FYI.

Friday, August 31 (DOY 243):

Science for the Titan flyby included CIRS measurements of CH4 levels in the
troposphere along with vertical profiles of temperatures in the stratosphere
and on the surface, a UVIS observation of the Titan occultation of Sigma
Sgr., a VIMS observation of the stellar occultation of alpha Sco and
AlpCMa., Titan very high resolution imaging, and ISS observations including
a regional map of Titan.

Sunday, September 2 (DOY 245):

Science observations over the weekend included CIRS Saturn IR mapping, ISS
Titan imaging, a UVIS mosaic of the Saturn inner magnetosphere, and a MAG
calibration.

Orbit Trim Maneuver (OTM) #125 was performed today.  This is the cleanup
maneuver from the Titan 35 encounter on Aug. 31.  The main engine burn began
at 6:00 AM PDT. Telemetry immediately after the maneuver showed the burn
duration was 2.98 seconds, giving a delta-V of 0.477 m/s. All subsystems
reported nominal performance after the maneuver.

Tuesday, September 4 (DOY 247)

A real-time command to perform a reaction wheel bias was sent up to the
spacecraft today.  The bias replaces the one that would have executed if
OTM-126 had not been deleted. 

The preliminary port for the S36 Science Operations Plan process occurred
today.  All teams have submitted the necessary files.  The final port for
this process occurs Sept. 12.

Final end-to-end testing for the Command Data Subsystem (CDS) Flight
Software version 10 began today and will run through September 11, 2007.
CDS V10 uplink to the spacecraft is set for the end of September as part of
the activities in S34.

Based on Spacecraft Office and Sequence Team recommendations, a real-time
command is to be sent to the spacecraft as a result of changes to the
Cassini DSN allocation file for the S33 background sequence now currently in
execution. The command will pause playback for appropriate durations during
shortened passes, and change the priority playback table.  Three passes
needed to be shorted to accommodate the needs of other missions:
DOY 256 - shortened by 20 min. at the front end
DOY 260 - shortened by 20 min. at the front end
DOY 263 - shortened by 35 min. at the front end

A feature on how the studies of atmospheric turbulence on Earth and on Titan
are each assisting the other is now available at:
http://saturn.jpl.nasa.gov/news/features/feature20070828.cfm

Wrap up:

Check out the Cassini web site at http://saturn.jpl.nasa.gov for the latest
press releases and images.

The Cassini-Huygens mission is a cooperative project of NASA, the European
Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a
division of the California Institute of Technology in Pasadena, manages the
Cassini-Huygens mission for NASA's Science Mission Directorate, Washington,
D.C.  JPL designed, developed and assembled the Cassini orbiter.


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