Cassini Significant Events 09/07/06 - 09/13/06

September 15, 2006

(Source: Cassini Project)


The most recent spacecraft telemetry was acquired Wednesday, Sept. 13,
from the Goldstone 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 at http://saturn.jpl.nasa.gov/operations/present-position.cfm .

Thursday, Sept. 7 (DOY 250):

The Titan 17 flyby (T17), at 1000 km altitude, occurred Sept. 7, 2006.
This flyby was at a latitude of 23 degrees, in a region where the Titan
atmospheric model predicted the atmospheric density to be greater than at
higher latitudes. The project anticipated thruster duty cycling between 40
and 65%, and developed an on-the-shelf reference trajectory to increase the
altitude of the T20 flyby should it be necessary. The duty cycle calculated
by AACS after the flyby was considerably lower than expected, around 20%.

Prior to closest approach, the Imaging Science Subsystem (ISS) searched for
and monitored lightning and aurora, and the Visible and Infrared Mapping
Spectrometer (VIMS) worked on Titan mapping, monitoring, and photometry, and
observed a stellar occultation through Titan's atmosphere.

Titan closest approach was designed with a spacecraft attitude suitable for
both Ion and Neutral Mass Spectrometer (INMS) data acquisition and a short
Synthetic Aperture RADAR (SAR) swath of Titan's surface. INMS data will be
used to help determine atmospheric and ionospheric thermal structure. The
Optical Remote Sensing (ORS) instruments used the time just after closest
approach to continue Titan global mapping and atmospheric analysis.

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) instrument performed under the Magnetospheric and Plasma Science
campaign to make inbound approach observations, provide context for the
interaction between Titan and Saturn's magnetosphere, and determine
atmospheric and ionospheric thermal structures.

Friday, Sept. 8 (DOY 251):

The S23 Saturn solar occultation Live Movable Block (LMB) kickoff meeting
was held today. A typical schedule for an LMB process runs from five to
seven days and looks something like this:

LMB kickoff meeting Friday (DOY 251)

Orbit Determination file available Saturday (DOY 252) at 2300 PDT

Epoch update and science analysis Sunday (DOY 253)

Go-No/Go meeting Monday (DOY 254)

Command Approval Meeting Tuesday (DOY 255) at 1600 PDT

Uplink Wednesday (DOY 256)

Execution beginning on Friday (DOY 258)

The S23 leads uplinked files for an Enceladus Live Inertial Vector
Propagator Update to execute tomorrow, Sept. 9, and a RADAR Enceladus
trigger. Both files have been verified onboard and should execute as
planned.

Today concluded the T17 encounter activities. The Imaging Science Subsystem
(ISS) used the Narrow Angle Camera to monitor surface and atmosphere changes
and attempt to see surface color variations on Titan. The spacecraft
performed a 9-hour downlink to the Goldstone 70-meter DSN antenna to play
back the Titan flyby data.

After playback, the spacecraft turned its attention to Saturn's rings and
Iapetus. The ISS instrument made a series of zero-phase Iapetus observations
and captured five Optical Navigation images. CIRS gathered temperature data
on the rings, while UVIS used the opportunity for spectral mapping of the
rings.

Saturday, Sept. 9 (DOY 252):

Non-targeted flybys of Atlas, Methone, Calypso, and Enceladus occurred
today. The Enceladus flyby was at an altitude of 39,932 km.

The first Cassini Radio Science Subsystem (RSS) Saturn gravity observation
in Orbit 28 concluded successfully today. The observation consisted of one
segment slightly over 6 hours in duration, and almost centered on periapsis.
This was the first of two RSS Saturn gravity observations during the Cassini
Tour that were selected as a pair. These two observations are specifically
optimized for measurement of the gravity field of Saturn. The second occurs
during Orbit 68 in May of 2008.

Sunday, Sept. 10 (DOY 253):

Orbit trim maneuver #71 was performed today. This was the T17 post flyby
cleanup maneuver. The main engine burn began at 12:23 PM. Telemetry
immediately after the maneuver showed a burn duration of 41.0 seconds,
giving a delta-V of 6.55 m/s. All subsystems reported nominal performance
after the maneuver. The next maneuver, OTM-072, is scheduled for Thursday,
Sept. 14.

Monday, Sept. 11 (DOY 254):

It turns out that S25 is in conflict with the Messenger Project on October
24, DOY 297, for Deep Space Station 14. Messenger has a critical event, the
Venus-1 flyby, on that day. DSS-14 is required by Messenger to downlink the
flyby data. The current proposal is for Cassini to keep the first 3 hours
over DSS-14 and then hand over to DSS-15 for the remaining 6 hours of the
pass. Messenger will then have the remaining 6 hours over DSS-14 for
downlink.

The Titan Atmosphere Model Working Group (TAMWG) met today to review the T17
Titan flyby results and to recommend whether the T20 closest approach
altitude should be raised. T17 is significant because it is, at closest
approach, the lowest latitude flown to date at 23=B0. The results from AACS,
INMS, and Navigation showed the atmospheric density significantly lower than
predicted. As a result, the previous model, which assumed an increase in
density near the equator, is under serious question.The flybys for T18 on
Sept. 23 and T19 on October 9 will be watched closely since these
altitudes were adopted assuming lower density at higher latitudes. However,
they are considered safe to fly based on the new information from T17. The
T20 altitude is not planned to be changed. The next two TAMWG meetings are
scheduled for Sept. 27 and October 16 after the T18 and T19 flybys.

The Science Operations Plan Update process for S27 kicked off today.

Tuesday, Sept. 12 (DOY 255):

A change board meeting was held today for AACS flight software version
A8.7.5. The four parameter changes approved were: secondary safing vector
pair update, A and B-branch thruster magnitude updates, Inertial Reference
Unit-A scale factor updates, and response script tier count change for a
potential fault protection case following an unexpected reaction wheel to
thruster transition.

The final approval meeting was held today for the S24 background sequence.
The instrument expanded block files will be uplinked beginning today with
the background sequence going up on Sept. 18.

The S23 Saturn solar occultation Live Movable Block was successfully
uplinked today and has been verified as registered onboard. The file should
execute as expected beginning on DOY-258.

The final development process began today for S26. The process will run for
ten weeks with uplink of sequence files occurring during the 11th week. S26
begins execution on Friday, November 24.

A beautiful image of Saturn at night is Astronomy Picture of the Day today.

Wednesday, Sept. 13 (DOY 256):

At the time S24 was going through the final development process, Uplink
Operations was unable to confirm the DSN allocations requested for the
sequence. The uncertainty was part of the STEREO launch and MRO aerobraking
conflict that the flight projects have been working with the DSN. Since the
allocations were uncertain, SSR data margin that is usually released for
instrument use during the development process was withheld, pending possible
station losses and the concomitant data cuts that would be required.

Now that the STEREO launch has been shifted to not earlier than October 25,
allocations are confirmed for most of S24, but not in time for the
instruments to take advantage of the now-available SSR data margin. The S24
leads are handling this by building a mini-sequence to be stored in the
movable block region of memory. It will run for most of the sequence from
DOY 269 through DOY 291. This file will contain the new data policing table
commands, all instrument commands required to take advantage of the sponge
bits, and any new instrument expanded block files required which go straight
to the instrument, and are not stored on the SSR. The mini-sequence will be
uplinked the day after S24 begins execution with a primary window of DOY
264/13:05-18:54, and a backup window of DOY 265/12:50-18:39.

The Magnetospheric and Plasma Science (MAPS) instruments continued the
magnetotail campaign to observe plasma flows and the dynamics of the
magnetotail from large distances downstream. The spacecraft is entering an
important phase of the mission that covers unique geometry optimal for MAPS
coverage of the magnetotail and plasma wake.

First viewed at the Saturn Orbit Insertion anniversary event held at JPL for
the flight team, the SOI +2 years highlights video chronicles some of
Cassini's discoveries in the last two years. To see it, go to: http://saturn.jpl.nasa.gov/multimedia/videos/video-details.cfm?videoID=128