From: VK1DSN@VK1DSN.ACT.AUS.OC
To : SPACE@VKNET
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.
------------------------
Visit the JPL Cassini home page for more information about the Cassini Project:
<http://saturn.jpl.nasa.gov/ >
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Posted by Rob vk1zqr@vk1dsn.act.aus.oc
Please use the same BID if re-posting...Thanks.
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