Cassini Update - July 17, 2009

Cassini Significant Events
for 07/08/09 - 07/14/09

The most recent spacecraft telemetry was acquired
on July 14 from the Deep Space Network tracking
complex at Goldstone, California. 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" page at:
http://saturn.jpl.nasa.gov/mission/presentposition/.


Wednesday, July 8 (DOY 189)

Part two of the S51 background sequence began
execution in the early hours this morning. S51 will conclude on July
23.

A kickoff meeting was held today for the S56
Science Operations Plan (SOP) process. The
process runs for approximately 15 weeks and will
conclude on Oct. 12 when it will be handed off to
Uplink Operations for final development and execution.

On Wednesday, July 8, Cassini flew by Titan at an
altitude of 965 kilometers and a speed of 6
km/sec. Closest approach for T58 occurred at
11:26 AM PDT at a latitude of 52.2 degrees S. T58
is the seventh flyby in a series of eleven
inbound encounters and the fourteenth Titan
encounter in Cassini's Equinox (extended) Mission.

During T58, the Ultraviolet Imaging Spectrograph
(UVIS) observed a long stellar occultation and a
solar occultation. The two observations probe
different parts of the atmosphere and are the
most valuable Titan observations for UVIS because
they provide detailed vertical profiles of
nitrogen using the Extreme Ultraviolet (EUV)
channel during solar occultations, and
hydrocarbons, HCN, and aerosols using the Far
Ultraviolet (FUV) channel during stellar occultations.

The solar occultation sampled the northern polar
vortex region from about 900 kilometers altitude
up to about 2,300 kilometers. This range overlaps
the atmospheric region sampled by the Ion and
Neutral Mass Spectrometer (INMS) and by Cassini's
attitude control system, or AACS. Solar
occultation measurements give a measure of the
density profile of N2, the main constituent of
the atmosphere, and the rate of change of the N2
density with altitude gives information on the
temperature. There has been a long-running
controversy about the density of the high
atmosphere. AACS consistently gets a higher value
than INMS and UVIS. This is one of the questions
to address with the data from these observations.

Both the solar and stellar occultations show a
complex picture of the upper atmosphere. Density
profiles and mixing ratios cannot be described as
a simple function of latitude and longitude.
There is more going on, perhaps gravity wave
activity, perhaps some other phenomena, which
make the upper atmosphere more variable than
simple models would predict. Continued
observations like the ones in T58 will help us sort out these issues.

With INMS riding along, the RADAR instrument
observed the western edge of Xanadu to study the
boundary with Shangri-La using Synthetic Aperture
Radar (SAR). The swath ran parallel to the
T55/56/57 mapping sequence and covered Ontario
Lacus. Altimetry observations of this same area
will be obtained by RADAR during the T60 flyby.

The Composite Infrared Spectrometer (CIRS)
performed a surface temperature scan and disk
integration to search for new gases in far-IR,
Imaging Science (ISS) acquired full-disk,
global-mapping, and regional-mapping mosaics of
the region southwest of Senkyo and northeast of
Tsegihi at low phase angles, and rode along with
the Visual and Infrared Mapping Spectrometer
(VIMS) for high resolution imaging and cloud
monitoring. VIMS ride-along observations
provided information on the composition of
Titan's atmosphere, and along with UVIS, observed
during a stellar occultation that will provide
information on the composition of Titan's atmosphere.

For the Magnetospheric and Plasma Science (MAPS)
instruments, the Magnetospheric Imaging
Instrument (MIMI) measured energetic ion and
electron energy input to Titan's atmosphere, and
the Radio and Plasma Wave Science (RPWS)
instrument measured thermal plasmas in Titan's
ionosphere and surrounding environment, searched
for lightning in Titan's atmosphere, and
investigated the interaction of Titan with
Saturn's magnetosphere. As in T55, T56 and T57,
Magnetometer measurements provided a description
of the draping and the pileup of the external
magnetic field around Titan on the night side
hemisphere. This data set will be a good
complement to those from T52, T53, T54, T55, T56
and T57 to characterize the background field for
similar local times with respect to Saturn and
different Saturn Kilometric Radiation longitudes.

Thursday, July 9 (DOY 190):

The Cassini Satellite Orbiter Science Team (SOST)
has requested the Project to perform the
Enceladus 9 flyby, scheduled for April 2010, on
reaction wheels instead of thrusters for more
accurate acquisition of Radio Science (RSS)
gravity data. AACS is evaluating the request and
will decide if the wheels have sufficient control
authority after the very similar E7 flyby on Nov.
5 of this year. SOST has proposed to perform
parallel sequence development of the
wheels/thrusters options so that products due for
port 1 of the S59 SOP process will not be
delayed. If the decision is that E9 will remain
on thrusters, SOST will alter the observations to
a MAPS flyby rather than an RSS flyby.

Friday, July 10 (DOY 191):

Weeks 35-36 and part of week 37 have been
negotiated for the S53 DSN station allocations.
One issue affects the Titan 61 dual playback
activity in August. The DSS-43 track scheduled
on DOY 239 has been lost due to a bearing
maintenance activity scheduled for the same
time. An extension of the DOY 239 DSS-14 track
plus a shadow DSS-63 track on DOY 241 to make up
for some of the lost data volume has been
negotiated. An SSR overage waiver will still be
needed and work on this waiver will proceed once
the allocation file has been released.

The first science activity today was one
observation in a CIRS campaign to study how and
how quickly ring temperatures change as the Sun
heats one side of the rings and then the other as
Saturn passes through equinox. This was followed
by two ISS observations: an AZSCAN to track
azimuthal variations in the rings and an
EQXSHADOW intended to utilize the low solar
elevation prior to equinox to look for shadows
cast by vertical structure within the rings.
Later in the week, ISS will be performing
MNRNGSHAD observations looking for shadows cast
by various moons of Saturn as they shepherd the
rings. While all this was occurring, the MAPS
instruments surveyed the inner portion of the Saturnian magnetosphere.

Saturday, July 11 (DOY 192):

A non-targeted flyby of Dione occurred today.

Sunday, July 12 (DOY 193):

Orbit Trim Maneuver (OTM) #206 was performed
today. This is the cleanup maneuver following the
Titan 58 encounter on July 7. The main engine
burn began at 10:38 PM PDT. Telemetry immediately
after the maneuver showed the burn duration was
20.75 seconds, giving a delta-V of 3.51 m/s, as
planned. All subsystems reported nominal performance after the
maneuver.

Monday, July 13 (DOY 194):

Files were due today for the Port 2 delivery as
part of the SOP process for S55. Spacecraft
Operations and Science Planning are currently
evaluating hydrazine use for conducting the
Enceladus 8 flyby - in November - on thrusters or
reaction wheels. The decision will be made before the Port 3
delivery.

The S55 Science Operations Plan process Port 2
delivery was due today. The merge will be
performed this evening with files distributed to
the team for review tomorrow. Files for the S54
Port 3 delivery are also due tomorrow.

The Integrated Test Laboratory performed a
simulation of the Titan 61 flyby this week to
enable RADAR to verify their observation plans.
RADAR is currently reviewing the test results and
c-kernel, and will report back with their findings.


Visit the JPL Cassini home page for more
information about the Cassini Project:
http://saturn.jpl.nasa.gov/
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