Cassini Update - February 25, 2005

Cassini Significant Events
for 02/11/05 - 02/23/05

The most recent spacecraft telemetry was acquired today from the
Goldstone
tracking station. 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
located at http://saturn.jpl.nasa.gov/operation...t-position.cfm .

Activities this week:

During the fifth week of S08, OTM-14 was successfully executed, Cassini
flew
past Enceladus for a non-targeted flyby, and passed through Saturn
periapsis.

Thursday, February 17:

This was a VERY busy day. The time-line looked something like this:
(In
Pacific time)

4:00 AM - The science folks bid a fond farewell to Enceladus as we
completed
closest approach and began the outbound leg of this flyby. Our next
opportunity for Enceladus science is a scant three weeks away! This
time,
however, it will be a targeted encounter.

6:00 AM - The Spacecraft Operations Office (SCO) takes center stage as
they
begin the final Maneuver Automation System run and publish the
resulting
Orbit Trim Maneuver (OTM) #14 files.

7:00 AM - Uplink Operations merges the files with a copy of the
background
sequence currently running on board the spacecraft. They then send
those
files out for Flight Software Development System testing.

8:00 AM - The OTM and background sequence files are published and
available
for the teams to run their checklists.

1:00 PM - Everything is due, checklists, presentations, etc.

3:00 PM - The Maneuver Approval Meeting is held followed by the Command
Approval Meeting (CAM). The difference is, at the Maneuver Approval
meeting
the Project says yes, this is the right maneuver to perform to keep us
on
the tour. At the CAM, the specific file names and uplink windows are
documented on uplink forms, and concurring signatures obtained. Once it
is
all signed off, the forms are delivered to the ACE in preparation for
radiation to the spacecraft.

5:00 PM - Is the beginning of track for the pass that will be used for
uplink. The files are sent, and confirmation received that they have
been
successfully registered on board.

11:09 PM - The burn executes. The purpose of OTM-14 is to clean up any
residual effects from the flybys and keep the spacecraft on its tour
trajectory. It is part of the Titan 3 through Enceladus, 8-maneuver
optimization chain.

This main engine burn was performed in the "blow-down" mode, where the
fuel
and oxidizer tanks were not directly connected to the helium pressurant
source. The burn began at 11:09 and ran for 4.583 seconds, giving a
delta-V
of 0.71 m/s.

The OTM-14 Maneuver Wrap-Up Meeting will be held tomorrow.

This is the process that occurs every time we have a maneuver. Only
the
times of day, on any day, vary. Hats off to the teams involved - SCO,
Navigation, Uplink Operations, and the Mission Support and Services
Office.
We are keeping them VERY busy.

Now let's talk about Enceladus! I'll give you some specifics about the
observations that were performed. For more information there is a
really
good write-up on the Cassini Web page that is less cut and dried, and
goes
into the interpretation of the data that was obtained. It's a news
release
called "Saturn's Moons Titan and Enceladus Seen by Cassini".

Roughly three hours before Enceladus closest approach, the Cosmic Dust
Analyzer (CDA) took measurements inside the E-Ring with an altitude to
the
Saturn ring plane between 190 km and 1140 km.

The Composite and Infrared Spectrometer (CIRS) had its first good
opportunity to search for possible endogenic activity that may be
associated
with the production of the E-ring material. In addition, the CIRS team
obtained their first good map of the dark side of Enceladus. This will
allow them to look for passive thermal anomalies associated with
surface
structural differences, e.g., with friable vs. highly consolidated
materials.

Optical Remote Sensing (ORS) observations and RADAR scatterometry and
radiometry measurements were performed to probe the geologic history
and
composition of the surface of Enceladus, measure surface temperatures,
look
for current thermal activity and investigate whether a tenuous
atmosphere
exists.

The Cassini Plasma Spectrometer (CAPS) observed electrons and energetic
ions
near the satellite.

Finally, during both the inbound and outbound legs of the flyby, Radio
Science (RSS) measurements were taken to constrain the mass of
Enceladus,
and to better understand the internal structure of this moon.

Two deliveries were made today as part of the Science Operations Plan
Update
process, official port #2 for tour sequence S11 and preliminary port
#1 for
S12. S11 was merged and delivered to ACS for end-to-end pointing
validation, and the merge report for S12 was published for the teams to
review and identify corrections.

Friday, February 18:

Earlier this month, SCO performed the first Inertial Reference Unit
(IRU)-A
calibration since the Probe was released from the Cassini Spacecraft
last
December. Three tests were performed where commands were sent to slew
the
spacecraft about the ?X-axis, ?Y-axis, and ?Z-axis.

This week a status report was issued on the tests. All were
successfully
executed with nominal results. In particular, the calibrated values of
the
scale factor errors, and the biases of IRU-A's gyroscopes meet the
established requirements. What all this means is, ACS has concluded
that the
impulse induced as a result of Probe separation did not adversely
impact
this set of important ACS sensors.

Outreach staff members attended a week-long conference sponsored by
NASA and
the Native American Academy. Titled "One Earth, One Universe" this
workshop
focused on the differences and similarities between western and Native
American science. This conference was the beginning of a dialogue with
the
objective of building a community that encompasses both of these
communities.

Monday, February 21:

Holiday.

Tuesday, February 22:

Today Uplink Operations hosted a Sequence Approval meeting where the
S09
background sequence and all 15 associated Instrument Expanded Block
(IEB)
files were approved for transmission to the spacecraft.

A Cassini-Huygens Analysis and Results from the Mission (CHARM) telecon
was
held where recent findings associated with Titan were discussed.
Sixty-nine
members of the community called into the talk.

Wednesday, February 23:

Uplink Operations has begun the radiation of the IEB files for S09.
Seven
Ion and Neutral Mass Spectrometer files were sent along with the
Ultraviolet
Imaging Spectrograph IEB before the command window closed. More files
will
be sent tomorrow night.

The Magnetospheric Imaging Instrument successfully submitted an ASP
command
request and radiated it to the spacecraft. ASP or Automated Sequence
Process allows instrument teams to directly command their instruments
without having to go through the "nominal" real-time command process.
The
set of commands each instrument is allowed to send is limited and has
been
reviewed to ensure they do not adversely interact with the system or
with
the other instruments. This capability will simplify operations for
the
instrument teams.

ISS and the Ultraviolet Imaging Spectrograph (UVIS) jointly observed
Dione,
Enceladus, Mimas, Rhea and Tethys. The Visible and Infrared Mapping
Spectrometer (VIMS) observed the G-Ring, and CIRS collected Mid-IR Maps
showing the temperature of Saturn's troposphere and tropopause.

In addition to the ORS observations, the suite of Magnetospheric and
Plasma
Science (MAPS) instruments simultaneously performed low-rate
magnetospheric
surveys.

Wrap up:

That's it for this week.

Due to the rain, the February 18 and 19 Pasadena and Monrovia telescope
viewing events reported in last week's report were postponed until this
weekend. Same time and place, on February 25 and 26, same weather
permitting
caveat.

Feb 25 Pasadena: Colorado Blvd near DeLacey 6 - 10 p.m.
Feb 26 Monrovia: Library Square, corner of Myrtle and Lime 6 - 10 p.m.

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.