Cassini Update - May 12, 2006

Cassini Significant Events
for 05/04/06 - 05/10/06

The most recent spacecraft telemetry was acquired Wednesday, May 10,
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 located at
http://saturn.jpl.nasa.gov/operation...t-position.cfm .

Thursday, May 4 (DOY 124):

On Wednesday, May 3, the Titan Orbiter Science Team (TOST) held a Titan
flexibility workshop to discuss possible changes to future Titan flyby
sequences based on the current data. No changes were made to the
existing
plans.

We all know Earth rotates once every 24 hours, but scientists have long
had
difficulty pinpointing how long a day is on Saturn. The Magnetometer
Subsystem (MAG) has, for the first time ever, measured a periodic
signal in
Saturn's magnetic field, key information to finally understanding the
length
of a Saturn day and the evolution of this gaseous planet. The latest
research suggests a Saturn day is 10 hours, 47 minutes, 6 seconds, plus
or
minus 40 seconds. That's 8 minutes slower than NASA Voyager results
from the
early 1980s, and slower than previous estimates from another Cassini
instrument. The magnetometer results provide the best estimate of the
Saturn
day to date, because it can see deep inside Saturn. These Cassini
results
can be found in the May 4 issue of the journal Nature. For more
information
link to:
http://saturn.jpl.nasa.gov/news/pres...cfm?newsID=656

Science Planning provided updated numbers for the data recovered from
the
Titan 13 flyby last week. Without the playback recovery plan in place,
the
science teams would have lost ~2500Mbits out of 3500, or approximately
70%
of the TOST segment, almost all of the closest approach data including
almost all of the Synthetic Aperture RADAR (SAR), and all of the
Ultraviolet
Imaging Spectrograph (UVIS) stellar occultation. With the playback
recovery
plan in place, this was reduced to ~600Mbits of TOST data lost, or
approximately 17%, and ~2100Mbits of Cross Discipline (XD) data
including
Icy Satellite and Rings data. Only the Visual and Infrared Mapping
Spectrometer (VIMS) data was saved of the XD set. Of the 600Mbits
lost,
almost 500Mbits of that was the earliest inbound data of the flyby and
only
about 100 Mbits were lost from -27 minutes to -12 minutes affecting the
start of the SAR swath.

NASA, the European Space Agency, and the University of Arizona have
released
a joint image advisory with two phenomenal movies. The movies show the
dramatic descent of the Huygens probe to the surface of Saturn's moon
Titan
on Jan. 14, 2005. To view the movies and for more information link to:
http://saturn.jpl.nasa.gov/news/pres...cfm?newsID=655

Friday, May 5 (DOY 125):

Cassini Outreach participated in two National Space Day events on May
4-5.
On May 4, over 3,000 students from Washington DC area schools as well
as
1,000 NASA Explorer school students and teacher teams attended a Space
Day
event at Goddard Space Flight Center. On May 5, over 15,000 students
and
families from the Washington DC and Northern Virginia area attended a
Space
Day event at the Smithsonian Institution's Udvar-Hazy Aerospace Museum
in
Washington DC. The Cassini Reading, Writing, and Rings DVD was
highlighted
at both events.

Uplink Operations sent commands to the spacecraft today for a Cosmic
Dust
Analyzer (CDA) decontamination exercise, and for a real time Reaction
Wheel
Assembly (RWA) bias to compensate for the cancelled Orbit Trim Maneuver
(OTM) #60. Both files are registered on-board the spacecraft and will
execute on DOY 128.

Sunday, May 7 (DOY 127):

OTM-60, originally planned for May 7, was deleted last November along
with
OTMs 48 and 54. This was done because there were only three DSN tracks
between the cleanup and apoapsis maneuvers, delivery errors did not
improve
after the apoapsis maneuver, and the maneuvers would be difficult to
cancel
in real time. The delta-V cost was about 0.8 m/sec.

Monday, May 8 (DOY 128):

The CDS Command Loss Timer (CLT) software patch will be uplinked
beginning
today and concluding Wednesday.

The Science Operations Plan Update kickoff meeting for S23 was held
today.
The process runs for five weeks and will conclude on June 9.

A very cool panorama of Huygens descending onto the surface of Titan is
Astronomy Picture of the Day today.

Tuesday, May 9 (DOY 129):

On Tuesday, May 9, an Enceladus Plume Debris working group held its
first
meeting. The primary goal of this group is to characterize the
Enceladus
plumes so that the Rev 61 flyby can be designed so as to not present a
hazard to the spacecraft. The work of this group is also important for
creation and analysis of possible extended mission tours. The group
needs to
develop a dust and gas engineering model that can be incorporated into
Mission Planning and Navigation software for planning flyby scenarios.

Wednesday, May 10 (DOY 130):

The Navigation Team has converged the orbit solution after OTM-059 to
the
point where it is clear that OTM-061 is a required maneuver with no
option
for cancellation. About a 20 km correction is needed to achieve the
desired
flyby for Titan 14. The current orbit determination solution
uncertainty is
less than 2 km and stable. Further, canceling OTM-061 would increase
the
total delta-V by about 9 m/s. OTM-061 will be targeted to the reference
trajectory flyby point.

Since this maneuver will bring us back to the reference trajectory, no
update to the Radio Science Subsystem Inertial Vector Definition file,
built
before the S20 uplink, will be required.

The CDS CLT software patch uplink activity was successfully completed
today.
This patch corrects a code error found last September that was
discovered
when the timer was set back for OTM-31, resulting in data loss for the
Titan
7 flyby. A temporary patch to restore normal operations was issued at
that
time; this patch fixes the code.

Since the Titan 15 to Titan 16 segment is very similar to the segments
where
Navigation recommended deletion of OTMs 48, 54 and 60, Navigation has
now
recommended the deletion of OTM-066. Program Management has concurred.
In
addition to reducing the number of maneuvers by one, the deletion
eliminates
work on the preceding weekend and saves about 0.15 m/s in the mean.
The
option to execute the maneuver and its backup on July 10 and 11 will be
maintained.

Wrap up:

Check out the Cassini web site at http://saturn.jpl.nasa.gov for the
latest
press releases and images.

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.