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Posted by baalke on April 20, 2007, 6:51 pm
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Cassini Significant Events
for 04/11/07 - 04/17/07
The most recent spacecraft telemetry was acquired on Tuesday, April
17,
from the Madrid 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, April 11 (DOY 101):
The official input port occurred today as part of the S32 Science
Operations Plan Update process. A Sequence Change Request (SCR)
approval
meeting was also held for S31. Fourteen SCRs were approved at this
meeting. No major issues are expected with incorporating them into the
sequence.
Cassini's magnetometer team has concluded that a leak in a helium lamp
in one of two detectors on the magnetometer caused the loss of one of
the detectors--the vector scalar helium detector-- after nearly nine
years of flawless operations. This detector is comprised of multiple
electronic components and one helium lamp. The detector has not been
operational since Nov. 2005, in spite of tests to turn the instrument
off and then back on at increasing time intervals. The second detector
continues to function at full capacity.
The magnetometer operated flawlessly throughout pre-flight testing,
Earth swing-by, cruise from Jupiter to Saturn, and the first year and
one-half in Saturn orbit. However, a gradual degradation that began a
year or more before Saturn orbit insertion in 2003 had been evident in
two housekeeping and engineering telemetry parameters that monitor the
output signals from the sensor.
The most probable cause of helium loss is a small puncture or crack in
the glass in the lamp that went undetected or resulted from damage by
a
micrometeoroid impact. The magnetometer scientific objectives in an
extended mission could be degraded by up to 15 percent, but the team
hopes to get additional calibration time to limit the impact to around
10 percent. The magnetometer was the first instrument to identify an
"atmosphere" around Saturn's little moon Enceladus, prompting the team
to move the trajectory in for a closer look, which led to the
discovery
of ice-gushing geysers erupting from its surface.
Thursday, April 12 (DOY 102):
With the Titan 28 flyby executed as planned, the Navigation team was
able to obtain a converged orbit determination solution based on the
first tracking pass after the flyby. Using this solution, Orbit Trim
Maneuver (OTM) #104 would have had a magnitude of 0.36 m/s. Since
OTM-105 has a mean value of about 3.5 m/s, the penalty for the
cancellation of 104 was only about 0.2 m/s, with the increases
occurring
in OTMs 107 and 110. Therefore, OTM-104, planned for execution on
Friday, April 13, has been cancelled.
Friday, April 13 (DOY 103):
The S34 aftermarket process kicked off today. This five-week process
will address proposed changes that require re-integration of the
segments contained in the S34 sequence. The initial Science Operations
Plan Implementation process was completed for S34 in July 2004 with
the
sequence archived and placed on the shelf for later development. Since
that time, a new CDS flight software update has been scheduled in the
S34 time period. There will be no science activity during the flight
software checkout period from 279T20:07 to 291T19:38. Instruments may
remain on but must be quiescent beginning with the DOY 279 downlink
pass. As a result, there may be a few changes to discuss for this
period.
Saturday, April 14 (DOY 104):
A Reaction Wheel Assembly (RWA) friction test of backup wheel #3 was
performed today. In this test, run every six months, the RWA is spun
up
to 600 rpm in both the clockwise and counterclockwise directions, and
then timed as it is allowed to run down to zero. Results showed no
significant change in either direction since the last test on Nov. 3,
2006. Run-down times remained above 40 minutes.
Monday, April 16 (DOY 106):
The winner of the most recent Cassini "Scientist for a Day" contest
visited JPL today. Jared Dmello, a 13-year-old from Columbia Middle
School in Adelanto, Calif., and seven classmates met with the Project
Manager and members of the science team to discuss his essay. The
students quizzed the team on the Saturnian system, and heard analyses
of
the three images taken as part of the contest.
Four students from Battle Academy in Chattanooga, Tenn., the authors
of
the runner-up essay, participated in the discussion via
videoconference.
They had selected a different image, argued their points with the
science team, and were equally full of questions. For writing the
winning essay, Jared received an autographed, poster-sized copy of the
image he had selected and argued for as the best scientific choice.
The
image depicts the rings and a rare appearance of both Atlas and
Daphnis,
two smaller moons in orbit around Saturn.
The next contest is scheduled for October 2007. For more information
on
Cassini's "Scientist for a Day," link to:
http://saturn.jpl.nasa.gov/education/edu-scientist.cfm
Tuesday, April 17 (DOY 107):
Today a kickoff meeting was held for the live Inertial Vector
Propagator
(IVP) update activity planned for DOY 114. The driving instruments for
this update are the Composite Infrared Spectrometer, Visual and
Infrared
Mapping Spectrometer, and Imaging Science Subsystem with targets of
Saturn and Dione. Science Planning analysis tools were run on the
orbit
determination solution based on not executing OTM-104. As expected,
results showed significant pointing errors starting on DOY 114. It is
anticipated that these pointing errors will be eliminated with the
execution of the live update. A go/no go meeting will be held tomorrow
and if approved, the update will be sent to the spacecraft on April
20.
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
Europe
an 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, Washingt on, D.C. JPL designed, developed and
assembled the Cassini orbiter.
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