NASA Cassini Significant Event Report for Week Ending 12/20/2004

The most recent spacecraft telemetry was acquired from the Goldstone
tracking station on Monday, December 20. The Cassini spacecraft is in
an
excellent state of health and is operating normally. As of today
(December 21), the Program is three days from Probe release and 25 days
from Probe relay.

The S07 background sequence began execution on Thursday December 16.
This sequence will run for 37 days and will end on January 22, 2005.
During this time, five Orbital Trim Maneuvers (OTM) will execute – one
of which is the Probe Targeting Maneuver. There will be one targeted
flyby of Titan, one non-targeted flyby of Iapetus, the Huygens Probe
will be released from the Cassini Spacecraft, and Probe Relay will
occur.

Science this week consisted of Saturn Magnetospheric studies performed
by the Cassini Plasma Spectrometer, Ion and Neutral Mass Spectrometer,
Magnetometer Subsystem, Magnetospheric Imaging Instrument and Radio and
Plasma Wave Science instrument.

On board activities this week primarily involved preparations for the
Huygens Probe separation event.   Orbital trim maneuver #8 was
successfully completed on the spacecraft on December 16. This
maneuver,
also called the Probe Targeting Maneuver, places Cassini on a Titan
entry trajectory in preparation for the Huygens probe mission. The
main
engine burn began at 6:30 p.m. Pacific Time. The “quick look”
immediately after the maneuver showed the burn duration was 84.9 sec,
with a delta-V of 11.9 m/s, as planned. ACS, Propulsion, and Thermal
teams all reported a nominal burn.

Also on December 16, the Huygens primary mission commitment meeting was
held. The participants were NASA, the European Space Agency, and JPL
management as well as Cassini and Huygens project management. The
participants reviewed the final report from the Mission Risk Review and
status and readiness assessments from both Cassini and Huygens. All
reports were favorable and the decision was made to proceed with the
primary Probe mission.

On December 19 and 20, the Probe Relay critical sequence was loaded to
the SSRs, the baseline High Gain Antenna pointing vectors were uplinked
for the Probe Relay sequence, and the Mission Timer Unit that will
activate the Probe shortly before atmospheric entry was loaded and its
countdown begun.

The Iapetus late update kick-off meeting was held this week. The files
will be uplinked to the spacecraft on December 30 for execution on the
31st. An Iapetus science preview meeting was held on December 20 to
present the science goals and plans for the upcoming close non-targeted
flyby on January 1.

Official port#1 occurred this week as part of Science Operations Plan
(SOP) Implementation of the S41 sequence. The team products are in the
process of being merged and will be delivered to ACS for the end-to-end
pointing validation after the New Year.

All sequence development including the Aftermarket, SOP Update, Science
and Sequence Update Process and SOP implementation processes stand down
for the period of December 18 through January 2. This decision was
made
to allow teams to focus on Probe Release operations and to squeeze in
time with their families.

The revised Mission Sequence Subsystem (MSS) D11 baseline plan, based
on
the final set of Engineering Change Requests (ECR), was presented at
the
Ground Software Monthly Management Review. There is one more likely
ECR
to be submitted for D11 addressing a data loss issue that arose in S06.

An image of Prometheus stealing particles from Saturn’s F ring and one
of an illustration of the Probe landing on Titan were Astronomy
Pictures
of the Day on December 17 and 20.

Image advisories, press releases and the latest Cassini information can
be found at http://saturn.jpl.nasa.gov.