Cassini Update - March 28, 2008

Cassini Significant Events
for 03/19/08 - 03/25/08

The most recent spacecraft telemetry was acquired on Monday, March 24,
from
the Madrid, Spain tracking complex. The Cassini spacecraft is in an
excellent state of health and all subsystems are 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.

Wednesday, March 19 (DOY 079):

An encounter strategy meeting was held today to cover the period
between
Mar. 25 and May 12, Titan flybys T42 and T43, and maneuvers 152-154.

Thursday, March 20 (DOY 080):

During the day today the Solid State Power Switch (SSPS) for Traveling
Wave
Tube Amplifier (TWTA) B Line A tripped off. The trip was detected
once
Cassini began receiving telemetry from a scheduled overnight DSN
pass. The
last safing event on the spacecraft, on September 11, 2007, was
triggered by
a trip of this same switch. This time, however, safing was avoided.
In the
new V10 CDS flight software, the SSPS / System Fault Protection (SFP)
interaction had been changed to allow the SSPS FP to take action
before
safing would be invoked. The software responded as designed by
commanding
the switch OFF to clear the trip, and then back ON. The TWTA and
spacecraft
are performing nominally following this activity. The CDS team will
send
real-time commands to the spacecraft on Saturday to clear the response
counter for TWTA-B line A.

This is trip #24, and the second one on this particular switch. Two
other
SSPSs have also tripped twice. These trips were predicted to occur at
a
rate of about two per year. Being in the Saturnian system has
accelerated
the SSPS trip rate for Cassini. Starting in April of 2004 until the
present, the trip rate has more than doubled compared to the cruise
period.

Cassini has discovered evidence that points to the existence of an
underground ocean of water and ammonia on Saturn's moon Titan. The
findings
made using RADAR measurements of Titan's rotation will appear in the
Mar. 21
issue of the journal Science. For the full news release link to:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=826

Friday, March 21 (DOY 081):

Today the Composite Infrared Spectrometer (CIRS) will target the rings
for a
longitudinal scan on the unlit face, outside shadow area, and at mid
phase
angle. Imaging Science (ISS) will target satellites in their
continuing
satellite orbit determination campaign.

Saturday, March 22 (DOY 082):

At the preliminary Orbit Trim Maneuver (OTM)-151 Navigation review,
the
required B-plane correction at Titan 42 was about 400 meters,
requiring a
correction of about 3.7 mm/sec (That's about 0.01 km/hr!), which is
well
below the minimum delta V capability. A quick look at the tracking
data
from Friday night's pass indicated a further shift of about 100 meters
in
the trajectory solution. This change was insufficient to increase the
delta
V to an acceptable level, about 14 mm/s. Science has reviewed the
trajectory
without the OTM and has not found any negative impact to science
acquisition. Therefore OTM-151, scheduled to execute today, has been
cancelled.

Sunday, March 23 (DOY 083):

Non-targeted flybys of Pallene, Epimetheus, and Methone occurred
today.

The main engine cover was closed today at the end of the OTM-151 prime
pass
for dust hazard avoidance. It will be reopened tomorrow at the start
of the
OTM-151 backup pass. This is the 38th cycling of the cover. A cycle
consists of deployment or closing of the cover, then stow or opening
of the
cover to a retracted position. The next cover closure is scheduled
for June
1, 2008.

The S38 sequence concluded and S39 began execution today. The
sequence will
run for 27 days and conclude on April 19. During that time there will
be
one targeted encounter of Titan and seven non-targeted flybys - two of
Pallene, and one each of Epimetheus, Methone, Titan, Janus, and Mimas.
OTM-152 is the only OTM scheduled to execute during this 4-week
period.

Today was a busy day for science, commencing with a CIRS radial scan
to
obtain ring temperature measurements over varying solar elevation and
phase
angles on both the lit and unlit sides of rings. CIRS also obtained a
longitudinal scan on the lit face of ring, in and around the shadows,
at low
phase angle. The Visual and Infrared Mapping Spectrometer (VIMS)
performed a
complete high resolution radial scan of the unlit face of the A, B and
C
rings at high phase angle, and observed the sun continuously as it
crossed
behind the east ansa, with coverage mostly of the A and B rings. ISS
captured a retargeted observation of specific gap edges and narrow
ringlet
structures. Some time was given to satellite observations, with VIMS
observing the lit surface of Dione and Mimas, and CIRS observing
Dione's
solar eclipse entry and Mimas's solar eclipse exit.

Monday, March 24 (DOY 084):

A beautiful picture of Saturn and Titan is Astronomy Picture of the
Day
today. Check it out at http://antwrp.gsfc.nasa.gov/apod/ap080324.html

A presentation was given today at JPL on "The Role of Tides on
Enceladus."

Science Operations Plan implementation for S44 began today. The
Science
Planning Attitude Spread *** (SPASS) will be delivered to the
instrument
teams on Mar. 26 so that they can begin working on the pointing
designs for
this sequence. The final Cassini DSN station requests will also be
delivered to the DSN schedulers that day.

Tuesday, March 25 (DOY 085):

Today Cassini flew by Titan at an altitude of 1000 km, and a speed of
6.3
km/sec. Closest approach (CA) occurred at 2008-085T14:28:48 SCET.
Just
prior to CA of this T42 flyby, the Ion and Neutral Mass Spectrometer
(INMS)
examined the upper atmosphere. Immediately after, VIMS captured images
of
Titan near the Huygens landing site using the so-called "noodle" mode,
where
VIMS captures a long noodle-shaped swatch of Titan's surface. CIRS
spent
eight hours looking at several positions on Titan's limb, measuring
stratospheric temperatures around one quarter of the visible disk, and
also
searching for new trace species. Additionally, CIRS rode along with
ISS to
obtain imagery of the landing site. Link to the following for more
information on this flyby:
http://saturn.jpl.nasa.gov/news/events/titan20080325/index.cfm

The Cassini-Huygens Analysis and Results of the Mission (CHARM)
teleconference for March addressed the topic of: Organics on Titan,
Water
on Enceladus: Worlds of Possibilities for Life.

The final sequence development process for S41 kicked off today. The
process will run approximately ten weeks and conclude just before the
start
of sequence execution on May 31. S41 is the final sequence in the
Prime
Mission.

Today a two-day NASA review began at JPL to assess Cassini operations
preparedness to support Extended Mission. The review will conclude
tomorrow. Update: At the end of the review on Mar. 26, the board had
found
no negative aspects to the Cassini operations plan. An official
report of
the board's findings will be released shortly.

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.


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