Cassini Update - February 3, 2012

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Cassini Significant Events
fof 01/25/2012 - 01/31/2012

The most recent spacecraft tracking and telemetry data in this reporting
period were acquired on Feb. 1 from the Deep Space Network 34 meter Station
26 at Goldstone, California. The Cassini spacecraft is in an excellent state
of health with all subsystems operating normally except for the known issues
with the Cassini Plasma Spectrometer and the Ultrastable Oscillator.
Information on the present position and speed of the Cassini spacecraft may
be found on the "Present Position" page at:

http://saturn.jpl.nasa.gov/mission/presentposition/ .

This week, command sequence S72 started its science observations with a
Titan Meteorological Campaign, in which the Imaging Science Subsystem (ISS)
looked for cloud events. The Ultraviolet Imaging Spectrograph (UVIS) then
executed slow scans in the extreme- and far-ultraviolet across Saturn's
illuminated hemisphere. The Visual and Infrared Mapping Spectrometer (VIMS)
concentrated on the remains of the storm in Saturn's northern hemisphere,
which has been raging since December 2010. Scientists think the String of
Pearls (http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20061011/)
may be hidden beneath the storm, and after the storm wanes will try to
discover whether the feature may have been destroyed by the tempest. ISS
then acquired images over a range of latitudes at low, medium, and high
emission angles as the planet rotated. (Emission angle is the angle between
the camera boresight and a line normal to the surface point being imaged;
straight down is zero degrees.)

The Composite Infrared Spectrometer (CIRS) mapped Saturn's prime meridian
from the north pole to the equator to determine the upper troposphere and
tropopause temperatures with spatial resolutions of about two degrees of
latitude and longitude. Following this, VIMS acquired a high spatial
resolution map of the dynamics of Saturn's deep atmosphere. VIMS imaged the
same area twice, measuring winds via motions of the clouds. Since these
observations were made while the spacecraft was near periapsis, clouds as
small as 300 kilometers wide were detectable.

RADAR mapped the same deep region at and around periapsis, obtaining
radiometry data at microwave wavelengths much longer than those seen by
VIMS. These RADAR maps looked for ammonia gas to reveal the variability of
this condensable constituent over the same area where VIMS mapped clouds
(formed either via chemical reaction with hydrogen sulfide, thus forming
ammonia hydrosulfide clouds, or via direct condensation into ammonia
clouds). Unfortunately, this carefully collected RADAR data set and most of
the corresponding VIMS data were lost when heavy Australian summer
rainstorms drowned out Cassini's signal while it was arriving at Earth on
Sunday, January 29.

Targeted Titan encounter T-81 then executed perfectly on January 30, as
detailed below.

Wednesday, Jan. 25 (DOY 025)

The S72 background command sequence went active on the spacecraft today. The
Cosmic Dust Analyzer instrument turned on heaters to perform a routine
15-hour long decontamination activity.

Thursday, Jan. 26 (DOY 026)

JPL flags flew at half-mast as a NASA-wide Day of Remembrance was observed
in honor of the Apollo 1, Challenger, and Columbia crews, as well as other
members of the NASA family who have died supporting NASA's mission.

The S74 Sequence Implementation Process kick-off meeting was held today.

Attitude and Articulation Control Subsystem (AACS) engineers read out the
spacecraft's Reaction Wheel Assembly revolution counter, and then reset it
to 0 counts. This is done about every six months to maintain an accurate
accounting of wheel usage and avoid rollover of the counter.

It was discovered that the Cassini remote Science Operations Planning
Computers in the ground system were unable to obtain data from some of the
servers at JPL that were upgraded last week. Additional server upgrades have
been postponed, and the previous version of software was re-installed to
restore service.

Friday, Jan. 27 (DOY 027)

Orbit Trim Maneuver 308, the Titan T-81 cleanup maneuver, is being prepared
this week to execute on Feb. 2 local time.

Saturday, Jan. 28 (DOY 028)

Cassini passed through periapsis this morning, about 206,000 kilometers
above Saturn's cloud tops, which is the closest point to the planet for this
orbit. Relative to Saturn, Cassini was traveling 58,187 kilometers per hour.

Sunday, Jan. 29 (DOY 029)

AACS executed a Reaction Wheel Bias maneuver while Cassini was not being
tracked from Earth. Using thrusters to maintain attitude, the reaction wheel
speeds were set to the required values.

Monday, Jan. 30 (DOY 030)

During the high-altitude Titan T-81 encounter, ISS performed high-resolution
observations around closest approach (31,131 kilometers) along Titan's
leading hemisphere at high southern latitudes, including a late view of
Ontario Lacus before the Sun sets for southern winter. ISS also "rode along"
(took advantage of instrument pointing) with CIRS inbound high-phase angle
observations and outbound observations over Titan's anti-Saturnian
hemisphere at low phase angles. This encounter provided one of Cassini's
last views of Titan's high southern latitudes. VIMS rode along with ISS
looking for lakes in the south polar region.

Inbound and outbound UVIS observations obtained an image cube of Titan's
atmosphere at extreme- and far-ultraviolet wavelengths by sweeping its slit
across the disk. These cubes provided spectral and spatial information on
nitrogen emissions, hydrogen emission and absorption, absorption by simple
hydrocarbons, and the scattering properties of haze aerosols. This was one
of many such cubes gathered over the course of the mission to provide
latitude and seasonal coverage of Titan's middle atmosphere and
stratosphere.

During the flyby, the Radio and Plasma Wave Science instrument (RPWS)
measured thermal plasmas in Titan's ionosphere and surrounding environment,
searched for lightning in Titan's atmosphere, and investigated the
interaction of Titan with Saturn's magnetosphere.

More details about this encounter are available at:

http://saturn.jpl.nasa.gov/mission/flybys/titan20120130/ .

Back on Earth, Cassini's 56th Project Science Group meeting convened at JPL
today; about 130 scientists are in attendance at various meetings and
workshops throughout the week.

Near the end of the day, AACS executed a Reaction Wheel Bias maneuver while
Cassini's high-gain antenna was off Earth-point.

Tuesday, Jan. 31 (DOY 031)

Starting at midnight Pacific time, Deep Space Station 14, the 70 meter
aperture at Goldstone, California, began capturing realtime tracking data
(Doppler and range for navigation), and playback of the telemetry that had
been stored on Cassini's Solid-State Recorder during the Titan T-81
encounter. All of the data were safely down by 11:00 a.m. local. For
background on telecommunications in general, see:

http://www.jpl.nasa.gov/basics/bsf10-1.php .

Since approach science began in January, 2004, there have been 258,340 ISS
images planned, commanded, acquired, and downlinked. Of these, only 8
percent have suffered any missing data. VIMS has acquired 128,946 cubes in
the same time frame, with a similar rate of loss. Raw images from ISS are
always posted online soon after receipt at:
http://saturn.jpl.nasa.gov/photos/raw/.

Visit the JPL Cassini home page for more information about the Cassini
Project:

http://saturn.jpl.nasa.gov/

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