Cassini Update - July 15, 2005

Cassini Significant Events
for 07/07/05 - 07/13/05

The most recent spacecraft telemetry was acquired Wednesday, July 13,
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 .

Activities this week:

Thursday, July 7 (DOY 188):

The Sequence Team leads for S12 sent commands to the spacecraft today
to
patch the Ultraviolet Imaging Spectrograph (UVIS) instrument expanded
block
(IEB) #5, and to check some Cosmic Dust Analyzer (CDA) settings prior
to the
Enceladus encounter next week.

An encounter strategy meeting was held today for the Enceladus2 through
Titan5 period. This includes Orbit Trim Maneuvers (OTM) 26, 27, and
28.
Topics for a strategy meeting include but are not limited to the
Navigation
schedule, deliveries, and reference trajectory, maneuver performance,
staffing, targeted encounter summary, past encounters, predicted orbit
determination accuracy, special events during the encounter, spacecraft
consumables tracking, main engine assembly cover strategy, DSN
coverage,
first time events, backup and contingency planning, instrument status,
and
so on. Even though Cassini is now up to OTM-25, nothing is taken for
granted and the preparation for each maneuver is carefully considered
prior
to approval.

Uplink Operations has released the merged products for OTM-25 with the
currently executing S12 background sequence. These are the products
that
will be used by the flight team to do their checklists. The maneuver
approval meeting is scheduled for 7:00 am Friday of this week with
uplink -
once approved - beginning at 9:00 am Pacific time.

The S12 DOY Live Inertial Vector Propagator (IVP) update kick-off
meeting
was held this morning. Later in the day Navigation released the orbit
determination solution for teams to review for this update. A go/no go
meeting will be held tomorrow.

Friday, July 8 (DOY 189):

The S15 official port occurred today as part of the Science Operations
Plan
Update process. A program briefing will be held on the contents of
this
sequence on July 20.

At the Live IVP Update Decision Meeting this morning for Rhea and
Enceladus,
Science Planning and the driving instruments present recommended a
"NO-Go"
for the DOY 195 Update. As part of the standard update process, science
planning along with each science team use the latest Navigation
trajectory
information to come up with a recommendation on whether the pointing
update
s needed or not. In this case, all teams felt the actual spacecraft
trajectory did not deviate significantly from the planned trajectory
used
when the pointing design was submitted several months ago. Therefore,
there
was no need to perform any near real-time updates to spacecraft
pointing.

OTM-25 was successfully completed on board the spacecraft today. This
"Enceladus 2 approach maneuver," together with OTM-24, places the
spacecraft
on the proper trajectory for the July 14, 175 km targeted flyby of
Enceladus.

The main engine (ME) burn began at 3:00 p.m. PDT. A "quick look" at
telemetry immediately after the maneuver showed the burn duration was
2.1
sec, giving a delta-V of 0.33 m/s. This is the shortest ME burn to
date.
All subsystems reported nominal performance after the event. OTM-25
was the
first use of the new Mission Sequence Subsystem (MSS) D11.0 OTM blocks
and
Maneuver Automation Software V5.0 software.

Saturday, July 9 (DOY 190):

Via commands in the background sequence, the Main Engine Cover was
closed in
preparation for dust hazard conditions around the Enceladus encounter
on
July 14. It will be opened again on August 2, the day before OTM-26.

Monday, July 11 (DOY 192):

The RADAR instrument was powered on to obtain distant full-disk
radiometry
of Titan. The next RADAR observation will be to participate in the Rhea
non-targeted flyby on July 14.

Real-time commands were sent to the spacecraft for a modification to
the CDA
Enceladus flyby activities, and to send a trigger command for the RADAR
scatterometry to be performed at Rhea.

An image advisory on Hyperion was released today. The image products
released include a movie sequence and a 3D view. The views were
acquired
between June 9 and June 11, 2005, during Cassini's first brush with
Hyperion. In both the movie and the 3D image, craters are visible on
the
moon's surface down to the limit of resolution, about 1 kilometer per
pixel.
The fresh appearance of most of these craters, combined with their high
spatial density, makes Hyperion look something like a sponge. Both
items
are available for viewing at http://saturn.jpl.nasa.gov or
http://www.nasa.gov/cassini.

With the Enceladus flyby happening this week, Cassini Outreach has
updated
the Enceladus moon and flyby pages. The links a

Enceladus moon page:
http://saturn.jpl.nasa.gov/science/m...s.cfm?pageID=5

Enceladus flyby page:
http://saturn.jpl.nasa.gov/news/even...0802/index.cfm

Tuesday, July 12 (DOY 193):

Last week at the Titan Atmosphere Model Working Group (TAMWG) telecon,
the
key topic of discussion was the appropriate altitude for the upcoming
T7
flyby in September. Because of variations in atmospheric density
observed
to date, there is no consensus model to predict the atmospheric density
to
be encountered at T7. Use of worst-case density values indicate that
the T5
altitude of 1025 km may not be safe for T7 with its far southern
hemisphere
latitude of closest approach, and might lead to spacecraft loss of
attitude
control and safing. The closer the spacecraft (S/C) gets to Titan, the
greater the atmospheric torque applied to the spacecraft. At some
point the
atmosphere becomes dense enough that the S/C cannot maintain its
orientation
while flying through it. Then it executes safing and has to find the
sun in
order to regain its proper orientation so that it can communicate with
Earth
again. Safing terminates the executing sequence, so all science
observations planned between the safing activity and when the sequence
is
resumed are lost. By raising the flyby altitude we essentially
eliminate
any chance of this happening because the atmosphere will be thinner.

Following the TAMWG meeting, a follow-on meeting was held to discuss
the
operational issues related to making this change. There were concerns
expressed about trying to accommodate changes for S13 when the sequence
is
so close to completion and there is limited time available to implement
changes. S13 is currently in the final development phase with sequence
approval scheduled for July 21, and uplink beginning on July 27.
However, a
schedule for product deliveries was developed that would allow the
changes
to be accommodated, and the decision was made to proceed with the
change. As
of today the target altitude for the T7 flyby has been officially
raised
from 1025 to 1075 km. An updated reference trajectory will be delivered
on
20 July for teams to begin making the necessary adjustments to S13 and
S14.

Commands were sent to the spacecraft today to enable Radio and Plasma
Wave
Science (RPWS) sounder operations and to load an Ion and Neutral Mass
Spectrometer (INMS) flight software patch and instrument expanded block
for
Enceladus.

The S14 preliminary cycle 1 merged sequence products were released
today for
team review. These include files necessary for the live moveable block
scheduled for that sequence. The cycle 2 products will be released on
July
15 so that teams may check their pointing designs against the new
reference
trajectory to be released on July 20. Teams have only one chance in the
cycle 2 phase to correct any flight rule violations or pointing designs
caused by flying the new trajectory.

Wednesday, July 13 (DOY 194):

The S13 preliminary cycle 2 products were released today as part of
sequence
development. These included products for the background sequence, live
moveable block (LMB) for DOY 214, and the combined background sequence
and
LMB.

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.