Cassini Update - January 26, 2006

Cassini Significant Events
for 01/19/06 - 01/25/06

The most recent spacecraft telemetry was acquired Wednesday, January
25,
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, January 19 (DOY 012):

A Program Control Change Board Review was held today to examine three
Engineering Change Requests. The Cassini Program Manager approved
"Maneuver
Automation Software V6.0 Requirements," "Cassini Coherency Transition
Playback Delay Tool Design," and "Remote Access Multi-mission
Processing &
Ground Environment software v2.4.1 - New Features." Approval is
currently
pending for " Mission Sequence Subsystem D12.0 Orbit Trim Maneuver
Blocks."

Friday, January 20 (DOY 013):

The final approval meeting for S18 was held today. Uplink of the
instrument
expanded block files will begin on Sunday evening, and the sequence
will
begin execution on January 27.

Saturday, January 21 (DOY 014):

A Reaction Wheel Assembly (RWA) friction test was performed today on
the
prime wheels, numbers 1,2, and 4. In this test, the prime RWAs are spun
up
to 900 RPM in both directions and are timed as they spin down to 0 RPM.
This gives an indication of RWA performance. The longer the spin down
time,
the better. The results of the test today were favorable. As compared
to
early 2004, RWA-1 showed a positive trend, RWA-2 showed no significant
change, and RWA-4 showed only a slight negative trend. The RWA-1
results
are particularly gratifying since it has recovered nicely from the big
friction spike observed in 2004. The prime RWAs are tested every three
months, and the backups are tested every six months. A test of the
backup
wheel is scheduled for January 26.

Monday, January 23 (DOY 016):

High winds at JPL forced the facility to close early due to potential
wind
hazards e.g., broken trees, loose building materials, etc. The
Laboratory
was closed to off-site visitors including the 110 Cassini scientists
who
were to visit for the 38th week-long Project Science Group (PSG)
meeting.
Although it was necessary to cancel the working group meetings planned
for
today, the PSG was able to resume with the plenary session scheduled on
Tuesday.

A member of the Spacecraft Operations Office Attitude Control Subsystem
will
present "In-Flight Estimations of Cassini Spacecraft Inertia Tensor and
Thruster Magnitude" at the AIAA/AAS Space Flight Mechanics Conference
in
Tampa, Florida, this week.

Instrument Expanded block files for S18 and the background sequence
were
uplinked to the spacecraft today by the sequence leads.

This morning the Spacecraft Operations Office received an email from
the DSN
notifying the Cassini Program that at present, the DSS-15 X Maser is
red due
to difficulties coming back from a power outage at Goldstone this
morning.
It may not return to operation until DOY 032. The S18 passes on DOY
029,
030, and 031 use DSS-15. In its current condition, the telemetry rates
in
the S18 background sequence cannot be supported and would need to be
reduced
to 27650 bps. This would leave an excess of just over 1 Gb of data
volume
over the three days. It is possible to carry over the data until DOY
036
when the SSR would be overfilled. Station personnel are attempting to
fix
the problem. In the mean time, Cassini Science Planning is working the
issue with the instrument teams, the sequence leads are examining
possible
customization of the background sequence and the generation of
contingency
files to drop the telemetry rates, and the DSN schedulers are hunting
for a
window where 70M coverage could be provided in which we could retrieve
the
data.

Wednesday, January 25 (DOY 016):

This week science observations included ISS spectrophotometry and phase
coverage of Dione, Enceladus, Iapetus, Mimas, Rhea and Tethys. For
Iapetus,
ISS also obtained good limb topography and geodesy coverage along with
a
good global color observation. The Ultraviolet Imaging Spectrograph
(UVIS)
rode along with these ISS observations to measure the ultra-violet
albedo
across a range of longitude and phase.

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.