Cassini Significant Events 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 Cassini¹s 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 Cassini¹s 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 Titan¹s 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.
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