Cassini Update - April 22, 2005

Cassini Significant Events
for 04/14/05 - 04/20/05

The most recent spacecraft telemetry was acquired Wednesday from the
Goldstone tracking station. 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 .

Activities this week:

The Titan 5 targeted encounter occurs on Saturday April 16.

Remember how I have been saying for the last two weeks that the flight
team
would be pulling off three Orbit Trim Maneuvers in 10 days? Well, that
was
until we cancelled one! Read on for more information.

Thursday, April 14:

Today there was an untargeted flyby of Saturn's satellite Pan.

The Main Engine cover was closed beginning around 11:00 PM Pacific Time
for
about 20 hours as a dust hazard avoidance precaution. The next time we
close the cover is in about two weeks on April 29. The cover will then
remain closed until our next maneuver in July.

Uplink Operations (ULO) radiated commands to the spacecraft to trigger
the
RADAR Instrument Expanded Block program for their Titan 5 Scatterometry
and
Radiometry observations.

Development for tour sequence S11 continued this week with a sequence
change
request (SCR) approval meeting. All seven SCRs were approved and are
now
being implemented by their respective teams.

Friday, April 15:

Untargeted flybys of Epimetheus, Mimas, and Calypso occurred today.

The Navigation team has announced that OTM-23, the T5 cleanup maneuver,
is
now a candidate for cancellation. It is possible that the maneuver
required
would be so small as to be negligible. DSN tracks at Madrid on Sunday
and
Goldstone on Monday will be used to obtain the necessary information to
make
a decision.

Since this is the first time a cleanup maneuver has been a candidate
for
cancellation, a preliminary cancellation meeting will be held on Monday
afternoon. The final decision will be made at the maneuver approval
meeting
on Tuesday morning. ULO was scheduled to uplink a live Inertial Vector
Propagator (IVP) update the week after OTM-23, and a live moveable
block the
week after that. Since these two activities affect instrument
pointing, and
since OTMs affect pointing as well, Science Planning will be
investigating
the impact of cancellation on these two events. The results will be
incorporated into the decision to cancel at the meeting on Tuesday.

Saturday, April 16:

The Titan 5 (T5) targeted flyby occurred today at the lowest altitude
thus
far of 1025 kilometers, and is the first low altitude pass in the tour
for
which the Ion and Neutral Mass Spectrometer (INMS) is the prime
instrument.

T5 is important for determining the minor neutral and ion densities,
and is
a critical first step in sampling the global composition of the
thermosphere
and ionosphere, and the thermal structure as a function of local time
and
latitude under varying magnetospheric input conditions.

T5 also provides a second good look at the sub-Saturn hemisphere,
including
the first high-resolution - less than 250 m/pixel - coverage by the
Imaging
Science Subsystem (ISS) over the sub-Saturn region. This will be
first
good look ISS has had at the quasi-circular ~1000 km diameter feature,
perhaps associated with an impact structure. ISS will also continue
global
monitoring and surface mapping coverage, wide-angle camera (WAC)
photometry
of haze properties, and a WAC movie of clouds in ride-along with
Ultraviolet
Imaging Spectrograph (UVIS). Eighteen hours before closest approach
there
is an outreach image opportunity of Saturn rise/set over Dione.

For this flyby UVIS will be obtaining an EUVFUV spectral image that is
part
of a series to map Titan's atomic emissions, acetylene distribution and
haze
properties.

The Cassini Plasma Spectrometer (CAPS) team reported that the T5
encounter
is the first low altitude flyby with prime or otherwise excellent
pointing
for +-25 minutes. This will allow CAPS to sound the polar (74 deg)
ionosphere to altitudes well below the ionospheric peak, and to study
the
plasma environment around the Titan/magnetosphere interaction. The high
latitude of closest approach means Cassini will be flying through the
Alfven
currents which couple Titan to the magnetosphere. Finally, CAPS will
continue to take high resolution data, with prime pointing, outbound to
120
Titan radii, observing the distant signatures of the Titan interaction,
such
as pickup ions escaping Titan's atmosphere.

Members of the Saturn Observation Campaign conducted over 60 special
events
honoring Astronomy Day today. Locally, Cassini Outreach held three
Saturn
Observing sessions reaching 950 attendees this week alone.

Monday, April 18:

An image of Enceladus and Saturn's rings edge on is today's Astronomy
Picture of the Day.

Tuesday, April 19:

It's official. Orbit Trim Maneuver 23 has been cancelled. Navigation
reviewed the latest orbit determination and maneuver solution this
morning
and confirmed yesterday's tentative decision.

Each time an OTM is cancelled you can expect to see that ULO uplinked
Reaction Wheel Assembly (RWA) bias commands. This is because the bias
that
would have been included with the OTM commands needs to be performed
anyway,
and is now sent up as a separate activity.

Along with commands to perform an RWA bias ULO uplinked commands for a
Magnetospheric Imaging Instrument (MIMI) motor test.

Wednesday, April 20:

Four SCRs were approved as part of S12 sequence development. Teams are
now
in the process of implementing the changes.

The Radio Science Team hosted a very exciting meeting where they
described
the purpose of the RSS Saturn Equatorial Occultations and the data they
expect to receive after the activities that will execute on May 2-3.

Wrap up:

Recently Cassini Outreach has been receiving requests for information
on
science results as part of the weekly significant events report. The
purpose
of the Cassini "SigEs" is to give a report of activities that occurred
that
week. But not to worry. Your questions were passed on to the Program
Manager. He provided the following information:

The things that we have learned from these observations are, to some
extent,
available now in the literature. A literature search would show most of
them. Probably the two most readable journals are Science and Nature,
which have featured us a few times since SOI. Another avenue for people
who
really want to get serious about this is to refer them to the Planetary
Data
System. We have a big data release headed there this coming July, and
more
to follow on a quarterly basis. Anyone seriously interested in the raw
data
and how to access it should get in touch with Outreach who will refer
them
to the appropriate individuals.

The new moons page for the Cassini website is now online. As of
Thursday
the 14th not all the links to the 34 different moons had been
implemented.
Outreach thought they should be there in a few days so give it a try!
Link
to:
http://saturn.jpl.nasa.gov/science/moons/index.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.