Cassini Update - November 11, 2005

Cassini Significant Events
for 10/27/05 - 11/01/05

The most recent spacecraft telemetry was acquired Wednesday, November
9,
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 .

Wednesday, November 2 (DOY 306)

A Cassini image of the slow dancing moons Epimetheus and Janus, along
with
Saturn's rings, is Astronomy Picture of the Day today.

The S19 Science Operations Plan Update kickoff meeting was held today.
The
process runs for five weeks and will conclude on December 9.

The Program has made the decision to delete three apoapsis Orbit Trim
Maneuvers (OTM) in advance: OTM-48 on January 2, 2006, OTM-54 on March
5,
2006, OTM-60 on May 7, 2006.
The decision to cancel was made because there were only three DSN
tracks
between the post-encounter 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 is about 0.8 m/sec.
The
early deletion, as opposed to real time cancellation, allows for the
elimination of the meetings, analysis, and preparation associated with
the
normal process of deciding to cancel or perform these maneuvers. Most
OTMs
are not candidates for such early cancellation because they either have
a
sizeable deterministic component or a significant probability of being
required in order to meet mission requirements.

Members of the RADAR instrument team gave a Cassini internal
presentation on
RADAR science results.

Thursday, November 3 (DOY 307):

This week on board the spacecraft several of the instruments turned
their
attention to Iapetus. The Imaging Science Subsystem (ISS) performed a
global
map, obtaining geologic, geographic, and topographic data, the
Ultraviolet
Imaging Spectrograph (UVIS) measured the UV albedo across various
longitudes
and phase angles, and the Composite Infrared Spectrometer (CIRS)
performed
observations with high spectral resolution integration for composition
and
for phase angle coverage. These were all relatively distant
observations
leading up to next week's closest approach point of around 417,000 km.
In
addition to their own Iapetus observations, the Visual and Infrared
Mapping
Spectrometer (VIMS) observed the E ring from 30-40 Saturn radii in
order to
build up spectra at different phase angles, and the Magnetospheric and
Plasma Science instruments were able to observe the dawn-side
magnetospheric
boundaries over a range of radial distances, as well as obtain solar
wind
data.

Friday, November 4 (DOY 308):

A command approval meeting was held today for S16 Instrument Expanded
Block
(IEB) loads for ISS, VIMS, CIRS, UVIS, the Cassini Plasma Spectrometer,
and
optical navigation. Uplink of these files to the spacecraft will begin
on
Tuesday, November 8, at 1:00 AM PST.

The Science Allocation Panel (SAP) meeting held today was not the usual
meeting for sponge bit allocation. Instead, due to a change from a 70
meter
to a 34 meter DSN station for the downlink on 2006-069, the meeting was
used
to determine how to reduce data volume by 335 Mb on that pass, the last
of
the S18 sequence.

The Solid State Power Switch (SSPS) on line 1 of Reaction Wheel
Assembly-4
(RWA) tripped off unexpectedly today 51 weeks after the last such trip
on
November 11, 2004. That time it was line 2 of RWA-1. These SSPS trips
have
been seen before and are believed to be caused by Galactic Cosmic Rays
(GCR). So far in the mission there have been 13 such trips, and they
are
predicted to occur at a rate of about two per year. There was no
impact to
spacecraft performance, as there are two SSPSs and power lines per RWA,
but
each line is capable of carrying the entire load. The tripped switch
was
brought back online by stopping the downlink roll, transitioning to
Reaction
Control System (RCS) control, thereby turning off all three reaction
wheels,
biasing the wheels, and going back to RWA control. About 35 minutes of
the
roll for science data acquisition was lost, but there was no
interruption of
the downlink telemetry. The spacecraft is operating normally following
this
activity.

Monday, November 7 (DOY 311):

The S16 Final Sequence approval meeting was held today. S16 will begin
execution on board the spacecraft on Saturday, November 12.

The Project has selected a Monopropellant Tank Assembly (MTA) recharge
date
of April 10, 2006. This recharge date allows the thrusters to be at
optimal
pressure to provide control authority for the planned 950 km Titan
flybys
starting with T-16 on July 22, 2006. Calculations showed that the
predicted
tank pressure after repressurization is about 406 psia. The hardware
is
designed and qualified to operate properly at 420 psia.

Tuesday, November 8 (DOY 312):

Uplink to the spacecraft of six IEBs began today. The activity is
scheduled
to complete tomorrow. Additional commanding included a Magnetospheric
Imaging Instrument automated sequence processor command, and a command
to
clear the CDS error logs.

Wednesday, November 9 (DOY 313):

Commanding continued today with uplink of the remaining IEB files, the
S16
background sequence, the S15 end of sequence real time RWA bias, and a
RADAR
IEB trigger.

A Tour Science talk was given today on recent Cosmic Dust Analyzer
science
results concerning Enceladus and the E-ring.

A delivery coordination meeting was held today for the Spacecraft
Operations
Office tool Flight Software Development System (FSDS) version 2.2.
FSDS is
a simulation environment for the Cassini ACS subsystem. It provides
the
user with a command line interface for visibility into the spacecraft
simulation, the flight software and the ground interface. Users can
retrieve and set variables in the hardware, peek and poke global
variables
in the flight software, and check telemetry values.

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.