Cassini Significant Events 04/11/07 - 04/17/07

April 19, 2007

(Source: Cassini Project)

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

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:

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.