Cassini Update - March 24, 2006

Cassini Significant Events
for 03/16/06 - 03/22/06

The most recent spacecraft telemetry was acquired Wednesday, March 22,
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, March 16 (DOY 075)

In the Meridian room of Dunsink Observatory in Castleknock, Ireland, a
Saturn Observation Campaign (SOC) member hosted 55 people for a
presentation
about JPL's Spirit of Exploration and the stunning images from the
Cassini
Mission. Unfortunately the evening's Saturn-gazing had to be cancelled
due
to appalling weather.

Thirty-five 2nd grade elementary school students, their parents, and
teachers gathered in Grossrinderfeld, Germany to view Saturn, the Orion
nebula and the Pleiades star cluster. Kids and parents alike said a big
"wow" after looking for the first time at Saturn and its clearly
visible
moons.

Friday, March 17 (DOY 076):

Uplink operations sent commands to the spacecraft today for the DOY 080
Rhea
Live Inertial Vector Propagator (IVP) update, and RADAR Instrument
Expanded
Block Update mini-sequence for Rhea. All files have been verified
onboard
the spacecraft.

Saturday, March 18 (DOY 077):

On March 18 the Cassini spacecraft conducted the 13th targeted flyby of
Saturn's moon Titan. With a closest approach altitude of 1,951 km,
this
flyby provided the first Cassini tour opportunity for Radio Science
(RSS) to
observe Titan's ionosphere and neutral atmosphere using radio
occultation,
and Titan's surface using bistatic scattering. The radio occultation
is the
second ever of Titan, the first being a sole Voyager occultation in
1980.

During approach to Titan, the Cassini high gain antenna boresight was
pointed to illuminate regions of Titan's surface for which mirror-like
reflections of the incident radio signals can be observed at the DSN
ground
receiving stations. The strength and polarization properties of the
reflected signals, if detectable, provide important information about
the
physical nature of the surface region probed, as well as the surface
roughness.

Radio Science has reported that the S- and X-band data is of
exceptionally
high quality. Both the large and small-scale structure of the
atmosphere at
the two observation latitudes are well captured in the data. The data
is
consistent among the multiple stations observing at the same time,
clearly
indicating that the structure observed is real and not noise. The
details
of the small-scale structure appear to be different for the ingress and
egress sides. Despite spacecraft pointing being controlled by
thrusters and
poor weather at both Goldstone and Madrid at the time, the Ka-band
amplitude
stability appears to remain surprisingly good throughout the
approximately
one hour observation period.

All indications are that T12 was remarkably successful, the first Titan
occultation in 25 years, the first at three wavelengths, and the first
Titan
bistatic experiment as well.

Tuesday, March 21 (DOY 080):

Orbit trim maneuver (OTM) #56 was performed today. This is the cleanup
maneuver from the Titan 12 encounter on March 18. The main engine burn
began at 9:30 PM PST. A "quick look" immediately after the maneuver
showed
the main engine burn duration was 2.71 seconds, imparting a delta-V of
approximately 0.44 m/s. All subsystems reported nominal performance
after
the maneuver.

This week Cassini had one of the closest Rhea flybys in the tour.
Optical
remote sensing observations, along with a RADAR block, were used to
probe
the surface composition and geologic history of the largest icy
satellite
orbiting within the magnetosphere and E-ring environment. In
particular, the
Ultraviolet Imaging Spectrograph (UVIS) conducted compositional
investigations of Rhea's surface and the "near-Rhea" environment to
search
for a tenuous atmosphere. The Cosmic Dust Analyzer (CDA) continued
with its
search for Saturnian dust stream particles. In addition to its icy
satellite high phase campaign, the Imaging Science Subsystem (ISS)
observed
the sub-Saturn hemisphere of Rhea at the best resolution of the prime
mission, as well as part of the surface in "Saturn-shine".

Today the Navigation Team released reference trajectory 060323 for
Project
use. The new trajectory was designed to raise the minimum Titan flyby
altitude from 950 km, and will be used in the Aftermarket Process for
sequence development of S23.

Wednesday, March 22 (DOY 078):

The final system mode end-to-end test for the Monopropellant Tank
Assembly
(MTA) recharge and ACS flight software A8.7.4 uplink activities began
today
and will conclude on Thursday. The recharge brings the thrusters up to
nominal thrust levels to provide control authority for the planned
lower
altitude Titan flybys, starting with T-16 on July 22, 2006.

Reaction Wheel Assembly (RWA) #1 exhibited three drag torque spikes so
far
in 2006 -- on February 8, and, more recently, March 15 and 16. Before
this
year, the last drag torque spike on RWA-1 occurred in 2001. RWA-1 has
been
troublesome in the past, exhibiting excessive drag torque in 2004,
although
a friction test on January 27, 2006 showed a positive trend since early
2004. The ACS team is keeping an eye on this.

The S21 Science Operations Plan update Project Briefing was held today.
S21
now moves on to the final sequence development process that will kick
off
Tuesday of next week.

A delivery coordination meeting was held for Navigation tool set T2.3.
This is an incremental delivery of multi-mission Navigation software.

A gorgeous picture of Enceladus hovering just above the rings was
Astronomy
Picture of the Day today.

Wrap up:

Check out the Cassini web site at http://saturn.jpl.nasa.gov for the
latest
press releases and images.

Do you want to know where Saturn viewing might be happening in your
area?
We have over 350 members of the Saturn Observation Campaign in 45
states and
49 countries around the world. Contact one of the SOC members in your
state
to ask when and where you can see Saturn.
http://soc.jpl.nasa.gov/members.cfm

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.