Cassini Update - December 15, 2006

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Cassini Significant Events 
for 12/07/06 - 12/13/06

The most recent spacecraft telemetry was acquired Wednesday, December 13,
from the Goldstone and Madrid tracking complexes. 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/operations/present-position.cfm .

Thursday, December 7 (DOY 341):

On November 2, Cassini used its 4000th DSN tracking pass since the
spacecraft was launched in October of 1997. The first 2837 passes were used
during the cruise phase prior to arrival at Saturn.

The last Cassini Monthly Management Review for 2006 was held today. At these
reviews, Program Management is informed of ongoing status through a series
of presentations by Resource Management, Scheduling, Outreach, Mission
Planning, Spacecraft Operations, Mission Assurance, Navigation, Mission
Support and Services, Telecommunications and Mission Services, and Science
and Uplink.

Two competing candidate plans were developed for the scientific observations
to be carried out on the T32 Titan flyby in June of 2007. One plan features
the collection of Ion and Neutral Mass Spectrometer (INMS) data, and the
other emphasizes Optical Remote Sensing (ORS) observations, in particular a
solar occultation egress measurement by the Ultraviolet Imaging Spectrograph
(UVIS) and the Visual and Infrared Mapping Spectrometer (VIMS). Members of
the Titan Orbiter Science Team (TOST) were unable to form a consensus as to
which plan to choose, and attempts to "merge" the plans in some way have not
been successful. The decision was handed over to the Project Scientist. What
made the decision difficult was the fact that both plans offer excellent
science at Titan. Also, with respect to Titan's surface and sensible
atmosphere, it is difficult to find a scientific criterion for choosing one
over the other. As a result, the Project Scientist fell back to the basics
of considering the project and the established science goals as a whole. The
following is extracted from the scientific objectives of the mission in the
NASA Announcement of Opportunity for Cassini:

Titan

- Determine abundances of atmospheric constituents (including any noble
gases; establish isotope ratios for abundant elements; constrain scenarios
of formation and evolution of Titan and its atmosphere

- Observe vertical and horizontal distributions of trace gases; search for
more complex organic molecules; investigate energy sources for atmospheric
chemistry; model the photochemistry of the stratosphere; study formation and
composition of aerosols;

- Measure winds and global temperatures; investigate cloud physics, general
circulation and seasonal effects in Titan's atmosphere; search for lightning
discharges;

- Determine the physical state, topography and the composition of the
surface; infer the internal structure of the satellite;

- Investigate the upper atmosphere, its ionization, and its role as a source
of neutral and ionized material for the magnetosphere of Saturn.

Magnetosphere

- Determine the configuration of the nearly axially symmetric magnetic field
and its relation to the modulation of Saturn Kilometric Radiation (SKR).

- Determine current systems, composition, sources, and sinks of
magnetosphere charged particles;

- Investigate wave-particle interactions and dynamics of the dayside
magnetosphere, and the magnetotail of Saturn and their interactions with the
solar wind, the satellites, and the rings;

- Study the effect of Titan's interaction with the solar wind and
magnetospheric plasma

- Investigate interactions of Titan's atmosphere and exosphere with the
surrounding plasma

Review of these objectives provided a clear way to resolve the "tie". Both
plans address, to some degree, the 1st, 2nd, and 5th Titan objectives. With
respect to the magnetospheric objectives, the INMS plan addresses the 4th
and 5th objectives. The ORS plan does not significantly address any of the
these objectives. The INMS plan was selected as it addresses more of the
mission's objectives.

Friday, December 8 (DOY 342):

A Dione, Pan, Saturn live update is now being planned to execute from DOY
348-350. This update was not officially scheduled at the time that S26 was
approved but has been carried on the books as a "possible" by Science
Planning. The observations during this time were just under the threshold of
the update limit when initial analysis of pointing variations in the
reference trajectory was performed. However, the variations have become
large enough to be over the live update threshold, hence the need for the
update. The kick-off meeting was held yesterday and the Go/No Go meeting for
today was cancelled, as all driving instruments wanted the update. The
mini-sequence will be uplinked next Tuesday, and the update will begin
execution on Thursday, December 14.

Monday, December 11 (DOY 345):

The Spacecraft Operations Office began a week-long final end-to-end test of
AACS flight software version A8.7.5. today in the Integrated Test
Laboratory. The software will be uplinked to the spacecraft in late January
or early February of 2007.

Tuesday, December 12 (DOY 346):

Cassini flew by Titan for the T21 encounter at an altitude of 1000km.
Traveling at a Titan-relative speed of 5.9 kilometers per second, Cassini
could travel from Los Angeles, CA to New York, NY in just over 11 minutes.

T21 is an upstream encounter with appreciable inclination with respect to
the equatorial plane. It is thus the first very close upstream pass and may
enable the Magnetospheric and Plasma Science (MAPS) instruments, especially
the Magnetometer (MAG), to study the magnetized ionosphere down to below the
ionopause on the upstream side. Additionally for MAG, this flyby has
considerable potential for internal magnetic field studies.

For this flyby the Synthetic Aperture RADAR (SAR) took a swath covering a
wide range of latitudes from just below the equator overlapping with the T8
swath and moving up to about 50 deg N. This image will be the only SAR image
in this region making it extremely valuable coverage. RADAR scatterometry
covered a wide range of incidence angles including the very valuable low
incidence angle range around the nadir point. It also extended down to the
south pole providing valuable south polar coverage, which is in short
supply. RADAR radiometry provided more coverage and polarization diversity
to help resolve the properties of Titan's surface materials.

Meanwhile, the Composite Infrared Spectrometer (CIRS) obtained a combination
of composition integrations in nadir mode and limb integrations in the
mid-infrared, and the entire suite of Magnetospheric and Plasma Science
(MAPS) instruments performed observations to study the interaction between
Titan and Saturn's magnetosphere.

Wednesday, December 13 (DOY 347):

The Spacecraft Operations Office held an AACS Flight Computer Reset tabletop
walk-through today. Walk-throughs are part of on-going training. This was
the latest in a series designed to acquaint, or re-acquaint, team members
with the behavior of System Fault Protection algorithms.

Official port 1 products were due today as part of the Science Operations
Plan Update process for S29. The joint Project Briefing and final sequence
development process kickoff meeting for S29 will be held on January 17.

JPL Media Relations supported a Titan news briefing for two dozen reporters
at the American Geophysical Union (AGU) meeting held this week in San
Francisco, CA. In conjunction with this briefing, a news release was issued
on the tallest mountains ever seen on Titan by the Cassini spacecraft. These
mountains appear to be coated with layers of organic material and blanketed
by clouds. To find out more link to: 

http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=709

At the Tuesday Ops Status and Coordination Meeting, Radio and Plasma Wave
Science (RPWS) team members reported that they had received science data
from the future, May of 2007 to be exact. Although amused by the report, the
flight team recognized that this could be a serious problem. In fact, it is
just the latest in a string of reports from the instrument teams regarding
recent problems with the data from DOY 336 -343. Command & Data Subsystem
(CDS) personnel have been reviewing the raw telemetry data and have
determined that the data corruption is due to double bit error hits in the
SSR memory after the data was recorded.

CDS monitors the hourly rate of Single Bit Errors (SBE) and Double Bit
Errors (DBE) on each SSR. A significant rise in the rates started on DOY
336, with a new high peak of 3820 SBEs per hour. This is coincident with a
strong increase in solar flare activity recently reported in the news. CDS
believes that the DBEs are a result of the solar activity, and there are no
indications of any CDS flight software problems or SSR memory degradation.
Double bit errors are temporary, being removed the next time the affected
memory is overwritten. SSR memory is not radiation hardened and some SBE and
DBE errors are expected. SBEs are corrected automatically by the SSR
hardware using Error Detection And Correction (EDAC) logic, but the DBEs
cannot be corrected and will result in some data corruption.CDS expects the
SBE and DBE rates to return to normal levels once the solar activity
subsides.

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 Spsce 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.
 

 




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