Cassini Update - January 20, 2006

Cassini Significant Events
for 01/12/06 - 01/18/06

The most recent spacecraft telemetry was acquired Wednesday, January
18,
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 12 (DOY 012):

On Christmas Eve, 2005, the Z sigma ratio exceeded its limit for 10% of
its
persistence time due to the star tracker's confusion when Rhea passed
through its field of view (FOV). This ratio compares the measured
star
brightness to that expected, and Rhea's interference was interpreted as
an
unexpected bright body. Since two of the four safing events we've had
on the
spacecraft were triggered by this Fault Protection (FP) monitor, the
Spacecraft Operations Office decided to take some action to prevent any
risk
of losing the upcoming Titan-10 encounter, where Titan itself would
appear
in the tracker's FOV and potentially cause a similar situation. We
masked,
and then unmasked, the Z sigma ratio FP monitor prior to T-10 on
January 11.
This masking prevents a call to safing but logs the event for future
analysis. This mask/unmask strategy was successful, and we are
investigating potential bright body interferences at future periapses.

Friday, January 13 (DOY 013):

All Cassini instrument teams have delivered 100% of the data that was
scheduled to be submitted for the January, 2006, archive delivery.
This
includes science and house keeping data acquired from January 2005
through
March 2005.

Saturday, January 14 (DOY 014):

One year ago today the Cassini/Huygens flight team was anxiously
waiting to
hear back from the Huygens Probe as it descended through the atmosphere
of
Titan. Here are some of the events from that day. All times
referenced
are Pacific Time.

12:10 AM - Loss of Signal from Cassini as it turns off Earth point to
Probe
relay attitude

2:12 AM - Probe begins transmission

3:25 AM - The Robert C. Byrd Green Bank Telescope (GBT) of the National
Radio-astronomy Observatory in West Virginia, USA, detected the probe's
'carrier' signal. Presence of this signal indicated that Huygens had
survived its high-speed atmospheric entry, the back cover must have
been
ejected, the main parachute deployed, and the probe had begun to
transmit.
In other words, the probe is "alive".

The parachute deployment sequence was initiated when the Probe reached
Mach
1.5, and a pyrotechnic charge was fired deploying a 2.59m pilot chute.
After
a 30 second delay to ensure the shield was sufficiently far away to
avoid
instrument contamination, the science packages deployed and began to
make
measurements of Titan's atmosphere.

After a further 15 minutes, the main parachute was jettisoned to avoid
a
protracted descent and a smaller 3.03 m diameter parachute was
deployed.

The descent lasted about 147 minutes. Five batteries onboard the probe
are
sized for a Huygens mission duration of 153 minutes, corresponding to a
maximum descent time of 2.5 hours plus at least 3 additional minutes on
Titan's surface.

7:04 AM - Cassini is now on Earth Point

7:06 AM - End of the Probe Relay Sequence


7:07 AM - Begin 1st Playback Sequence

7:14 AM - Begin Solid State Recorder (SSR) Partition B4 Playback.
Data
from Huygens was relayed to the Cassini Orbiter passing overhead and
stored
on the SSRs. Closest approach distance was 60,000km.

10:00 AM - B4 Playback Complete

The probe signal was lost before the batteries expired, and before the
orbiter went over the horizon - loss of signal was due to the probe AGC
dropping below threshold due to the orbiter moving out of the
beam-width of
the probe antenna.

Radio Science/ Very Long Baseline Interferometry (VLBI) stations
continued
to receive data after loss of signal at the orbiter. After GBT set,
Parkes,
a 64-m radio telescope in Australia, received and recorded also via a
Radio
Science Receiver borrowed from the Canberra DSN complex. Parkes
recorded the
signal for over three hours after probe landing and set at 8:00 AM
while the
Probe was still transmitting and the signal was still present.

In addition to the GBT, sixteen other radio telescopes in Australia,
China,
Japan and the USA were involved in tracking the Huygens probe.

In the course of analyzing the data from the SSRs, it was determined
that
Huygens collected 2:27:13 of descent data, and 1:12:09 of surface data
- far
more surface data than was expected.

Not a single packet was dropped due to the Huygens receiver problem;
this is
a tribute to the mission redesign effort.

Sunday, January 15 (DOY 015):

Today Cassini executed the 10th targeted flyby of Titan at an altitude
of
2043 kilometers. The Composite Infrared Spectrometer (CIRS) observed
the
northern limb at +55 degrees latitude both on the inbound and the
outbound
legs. This is expected to be on or near the transition to a possible
winter
polar vortex region over the northpole. CIRS also performed
hemispheric
temperature mapping in the stratosphere, increasing temporal coverage,
and
also adding the spatial coverage of the far-infrared composition
mapping.

Especially exciting scientifically for the Visual and Infrared Mapping
Spectrometer (VIMS) instrument was the opportunity for a 64X64 cube
mosaic
of Titan's surface within 2 hours of closest approach. This
opportunity
allowed VIMS more high resolution data in an effort to better
understand the
surface geology and chemistry of Titan, and to continue the search for
surface liquids and evidence of cryovolcanism. The targeted areas
included
the Huygens Landing Site, Xanadu, and the "Snail" feature previously
imaged
by VIMS.

At precisely 40 minutes before closest approach, the Ultraviolet
Imaging
Spectrograph (UVIS) instrument performed its first solar occultation to
measure the compositional variations with altitude in Titan's upper
atmosphere. More specifically, with this occultation UVIS observed the
extreme ultraviolet (EUV) spectrum below 110 nanometers to sample
opacity
from nitrogen and methane and possibly some other hydrocarbons.

The Imaging Science Subsystem (ISS) acquired a mosaic of Titan's
anti-Saturnian hemisphere, including Shangri-la, Dilmun, Mindango,
Shikoku,
and Antilia Faculae. ISS also performed a higher-resolution mosaic of
the
western portions of Dilmun and Shangri-la of which may provide stereo
with
later ISS observations of Antilia Faculae.

The entire suite of Magnetospheric and Plasma Science (MAPS)
instruments,
which includes the Cassini Plasma Spectrometer (CAPS), Cosmic Dust
Analyzer
(CDA), Ion and Neutral Mass Spectrometer (INMS), Magnetometer Subsystem
(MAG), Magnetospheric Imaging Instrument (MIMI) and Radio and Plasma
Wave
Science (RPWS), also participated in this Titan encounter as they
measured
different aspects of Titan and its interaction with the magnetosphere.
MAG
was able to take full advantage of this encounter, as it was upstream
of the
Titan/magnetospheric interaction. The spacecraft flew through Titan's
middle ionosphere. Together with the T8 and T6 flybys, T10 will allow
MAG
to reconstruct the upstream equatorial ionospheric pile-up region.

MIMI observed details of the Titan/magnetospheric interaction within a
one-hour period of closest approach. MIMI also observed Titan's
exosphere/magnetospheric interaction by imaging energetic neutral atoms
(ENA) with the Ion and Neutral Camera (INCA). INMS obtained data
regarding
Titan's atmospheric and ionospheric composition and thermal structure.
This
observation will also help INMS piece together the fundamentals of the
magnetospheric/ionospheric interaction. RPWS studied the interaction
of the
magnetosphere with Titan at intermediate distances for evidence of ion
pickup, radio emissions, density profiles, and the general wave
environment.

Tuesday, January 17 (DOY 016):

Orbit Trim Maneuver (OTM) #50, the Titan-10 cleanup maneuver planned
for
January 18, 2006, was cancelled. This was the third cancelled OTM in a
row.
OTM-48, planned for January 2, was deleted in early November; OTM-49,
the
Titan 10 targeting maneuver, planned for January 12, was cancelled due
to
extremely small magnitude and duration, and OTM-50 was insignificant as
well.

A command approval meeting was held today for the eight instrument
expanded
block files to be uplinked to the spacecraft in support of S18. The
commands will go up beginning on January 22, and the sequence will
begin
execution on January 27.

Live update kick-off meetings were held today for both the third and
final
Inertial Vector Propagator (IVP) update in S17 and the first IVP update
to
execute in S18. Pointing analysis taking into account the cancellation
of
OTM-050 confirmed that both updates were unnecessary.

Periapsis for orbit 20 occurred today. At this time, RPWS was on a
campaign to look for dust impacts, lightning whistlers - very low
frequency
radio waves generated by lightning - and measured the variation of
plasma
density inside of about 9 Saturn Radii using the upper hybrid resonance
band.

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.