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Posted by baalke on September 14, 2007, 8:20 pm
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Cassini Significant Events
for 09/05/07 - 09/11/08
The most recent spacecraft telemetry was acquired on Tuesday,
September 11,
from the Goldstone tracking complex. The Cassini spacecraft is in an
excellent state of health and all subsystems are operating normally,
given
the configuration established by the safing. 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, September 5 (DOY 248):
An encounter strategy meeting was held today to cover the period from
Sept.
10 to Oct. 2, Iapetus 1 to Titan 36, and maneuvers 128-130.
Thursday, September 6 (DOY 249.):
The Navigation Team Chief has reported that the orbit determination
uncertainties have converged to the level of the Iapetus ephemeris
uncertainty, with the result that further improvement in the Iapetus
delivery accuracy is not expected. The UVIS star occultation
observation
just prior to closest approach exists with or without Orbit Trim
Maneuver
(OTM) 127. Using tracking data through today, OTM-127 has a magnitude
of
25.6 mm/sec. The downstream cost of cancellation is 17.5 mm/sec. Based
on
the minimal delta V cost of cancellation, the decision was made to
cancel
the maneuver. The maneuver would have executed on Sept. 8. A
reaction
wheel bias will be sent to the spacecraft to replace the one what
would have
been executed as part of the maneuver.
Friday, September 7 (DOY 250):
The Aftermarket process for S37 has now completed. The next major
activity
in development for this sequence, the Science Operations Plan Update
Process, will begin in about a week.
Monday, September 10 (DOY 253)
Fabulous raw images of Saturn's moon Iapetus are now available on the
Cassini web site. The raw image area is the most popular link on the
Cassini-Huygens Mission to Saturn and Titan web site. Go to this
link:
http://saturn.jpl.nasa.gov/multimedia/images/raw/index.cfm
Under Target, select Iapetus, and at the bottom click the button to
search
for images. A new world awaits you.
Here are some additional sources of information available regarding
this
flyby:
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=774
http://saturn.jpl.nasa.gov/news/events/iapetus/index.cfm
http://saturn.jpl.nasa.gov/science/moons/moonDetails.cfm?pageID=7
http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=773
Closest approach occurred on Sept. 10 at an altitude of 1644 km -
nearly 100
times closer than the non-targeted flyby in 2004 - and a speed of 2.4
km/sec. This is the first and only targeted encounter of Iapetus in
the
prime or proposed extended mission for Cassini. Early on, scientists
and
science planners identified two periods as being "high value" science
for
this flyby:
Observation Period 1: 2007-253T08:45:00 to 2007-253T20:05:00 SCET
Observation Period 2: 2007-253T22:20:00 to 2007-254T05:30:00 SCET
Instrument observations included RADAR scatterometry and radiometry,
Imaging
Science Subsystem limb topography and imaging, Composite Infrared
Spectrometer high spectral resolution integration for composition and
phase
angle coverage, and Ultraviolet Imaging Spectrograph observations to
determine the UV albedo of Iapetus' surface. In addition, the entire
suite
of Magnetospheric and Plasma Science instruments simultaneously
performed
outer magnetospheric survey observations.
In order to ensure against any data loss, the sequence was developed
so that
all of the high priority data would be played back twice.
Members of the flight team organized a presentation to occur on
Tuesday in
Von Karman Auditorium at JPL to give background on Iapetus to JPL
employees
and to view the raw images with live narration from some of the
Cassini
scientists.
Tuesday, September 11 (DOY 254)
After all the science observations during the encounter were complete
and
the data were safely stored on the solid state recorders, playback of
the
data began. Twenty-one minutes into this data downlink, the spacecraft
executed a safing routine to put it into a state called "safe mode".
The
cause was Traveling Wave Tube Amplifier RF Loss, triggered by a Solid
State
Power Switch (SSPS) trip, most likely caused by a galactic cosmic ray
hit.
Tuesday morning, commands were sent to the spacecraft to resume high
rate
science and engineering data playback. The project received all of the
data
on the spacecraft downlinks on Tuesday and Wednesday, with no impact
on the
Iapetus science data return beyond a brief delay.
In the course of executing the safing routine, the spacecraft turns
off all
nonessential activities and transmits only engineering telemetry at a
low
data rate while it awaits commands from Earth. Due to the safing
event, the
S33 sequence executing on the spacecraft was halted and the science
instruments were turned off. The last time Cassini executed safing was
over
four years ago during the execution of the C37 sequence. The SSPS trip
was
number 21 on the spacecraft since launch and the first since November
26,
2006
UPDATE:
At an anomaly resolution meeting on Wednesday, Sept. 12, the flight
team and
Project management selected the third of three options to follow to
resume
the S33 sequence execution and science data acquisition.
A mini-sequence will be sent to Cassini on Thursday, Sept. 13, to
execute
OTM-128. After that, the flight team will spend the next three days
sending
commands to reconfigure the spacecraft, turn on and load the science
instruments, and turn the S33 background sequence back on. It is
expected
that all will be back to business as usual by Sunday, DOY 259T21:09:37
SCET.
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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