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Cassini Significant Events for 03/17/05 - 03/23/05



Cassini Significant Events
for 03/17/05 - 03/23/05

The most recent spacecraft telemetry was acquired today 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/operations/present-position.cfm .

Activities this week:

Science activities this week included a magnetospheric boundary campaign
performed by the Cassini Plasma Spectrometer (CAPS), Cosmic Dust Analyzer,
Ion and Neutral Mass Spectrometer, Magnetometer Subsystem, Magnetospheric
Imaging Instrument (MIMI) and Radio and Plasma Wave Science subsystem.
These six instruments represent the entire suite of Magnetospheric and
Plasma Science Instruments.

Optical Remote Sensing contributed mosaics of Saturn's inner magnetosphere
taken by the Ultraviolet Imaging Spectrograph, and Iapetus limb topography
and geodesy recorded by the Imaging Science Subsystem (ISS).

Thursday, March 17:

A contrast-enhanced image of the surface of Enceladus was Astronomy Picture
of the Day today.

The Mission Sequence Subsystem (MSS) team began user acceptance testing for
version D11 software.   D11 will be delivered in May and is the Project's
last big delivery for new capabilities. All MSS deliveries in the future
will be maintenance only.

Mission Planning hosted a session to discuss the possibility of lowering the
flyby altitude for the Tethys encounter in September of this year.  There
are a number of trades and concerns to be examined with this issue.  Among
them are the science advantages of a closer flyby, impact to operations
personnel if a new reference trajectory is delivered to support this change,
impact to the science and sequence teams if extensive modifications to S14
are necessary, optical remote sensing of Tethys versus atmospheric science
of Saturn, as well as the use of consumables.  A decision meeting for this
issue will be held Friday of next week.

System Engineering coordinated a MIMI flight software random access memory
patch meeting.  The patch is in response to an issue regarding the Low
Energy Magnetospheric Measurement Subsystem (LEMMS) sensor.  At times, the
sensor stops communicating with the main electronics.  The fix is to power
cycle the LEMMS.  The purpose of the patch is to have the code issue the
power cycle instead of having to send up real time commands.  The patch was
approved and will be uplinked tomorrow.

System Engineering also led a Ground Software Status Monthly Management
Review today. The Teams and Offices reported readiness for the D11 Spring
delivery and installation along with Deep Space Mission Systems D14.1 with
new TPS and Telemetry, Tracking, Command & Data Management.

The Navigation Team delivered their final orbit determination solution for
Orbit Trim Maneuver #18 (OTM). OTM-18 will execute over the weekend.

Friday, March 18:

Uplink Operations (ULO) sent real-time commands to the spacecraft for a MIMI
LEMMS flight software patch and motor test, a CAPS actuator test to
articulate to +90 degrees, and an ISS trigger overlay mini-sequence

As part of S10 development, ULO delivered the Live Movable Block (LMB)
mini-sequence containing the Radio Science Subsystem and Visual and Infrared
Mapping Spectrometer requests, and the current version of the S10 background
sequence that doesn't include the LMB activities.

ISS delivered an updated version of instrument flight software to the
Project Software Library.  One fix and one enhancement were made to improve
robustness.  A final run in the Integrated Test Laboratory will occur prior
to the final delivery review on April 15.

Saturday, March 19:

Cassini's fifth orbit around Saturn began today.  Rev 5 is 18 days long and
will conclude at the next apoapsis on April 6 when Rev 6 will begin.

OTM-18 was performed on the spacecraft this morning.  This apoapsis maneuver
targets the spacecraft to the proper trajectory for the March 31 Titan flyby
at an altitude of 2,402 km.  The main engine burn began at 11:31 a.m. PST.
A "quick look" at telemetry immediately after the maneuver showed the burn
duration was 10.4 sec long, giving a delta-V of 1.6 m/s. All subsystems
performance was nominal.

Monday, March 21:

All products for preliminary port two were delivered as part of the Science
Operations Plan Update process for the S12 sequence.   The files were merged
and the resulting files posted for review.

Today at the Project Science meeting a lively discussion was held about the
possibility of a Tethys tweak - see the entry from Friday, March 18.  After
the discussion, a consensus emerged that the delta V for this proposed
change should be kept at or below 10 m/sec or the equivalent of about one
Titan flyby, and the Radar atmospheric science in this time interval should
be preserved.  Project discussions are continuing before a final decision is
reached.

Tuesday, March 22:

At the Mission Planning Forum today Navigation gave a presentation on the
estimated duration of an extended mission based on the characteristics of
the nominal mission - number of encounters, and number of days between
encounters - and predictions of how much bi-propellant will still be
available in 2008.

Some additional Tethys tweak information was also provided at the Mission
Planning Forum along with the latest Consumables update.  Mission planning
tracks the "consumables" for the spacecraft and instruments.  This includes
main engine cover cycles - how many times we close and open it to protect
the engines -, how long instruments have been powered "on" since launch,
instrument articulations, use of reaction wheels, etc.

OTM-18 is looking so good that there's a possibility that Navigation will
recommend canceling OTM-19, the T4 approach maneuver.  In a possible
maneuver cancellation situation, Navigation provides two orbit determination
(OD) solutions.  One shows the trajectory that will happen if we do the
maneuver, and another trajectory that will happen if we don't.  Pointing
plots are also provided showing the difference between what was planned,
what will happen, and the uncertainty of the trajectories.  Science Planning
will provide COVT plots showing the fields of view for each Science Planning
Attitude Spread Sheet prime request for both trajectories.

The teams then evaluate these plots and provide feedback to the sequence
leads.  In this case, the S09 leads with a due date of Thursday March 25 for
the 3pm meeting.  The Program may repeat the whole thing for ODs delivered
on Thursday, but in previous situations the input from the distributed teams
in the first meeting was sufficient.  We did the exact same thing for the
approach to Enceladus maneuver and ultimately the maneuver was cancelled.

Wednesday March 23:

An assessment meeting was held today as part of the Science Planning
Aftermarket process for S14.  The purpose of the assessment is to determine
if the requested changes fit within available resources.  The proposed
"Tethys Tweak" would occur in S14. The consensus of participants was that
changes were in the ballpark for workload with regards to the standard S14
changes, and the changes that will be required for the Tethys Tweak.
However, the S14 Science Planning lead requested that all participants
respond with a specific impact to workload given the modifications that
would need to be made.  The plot thickens?   Stay tuned for next Friday's
decision meeting on this issue.

Wrap up:

The most recent spacecraft telemetry was acquired Wednesday from the
Goldstone tracking station.  The Cassini spacecraft is in an excellent state
of health and all subsystems are operating normally.  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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