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NASA Cassini Significant Events 09/19/2012 - 09/25/2012

Status Report From: Jet Propulsion Laboratory
Posted: Friday, September 28, 2012

image The most recent spacecraft tracking and telemetry data were collected on Sept. 25 by the Deep Space Network's 70 meter Station 14 at Goldstone, California. Except for the Cassini Plasma Spectrometer, which is off, and the failed Ultrastable Oscillator, the Cassini spacecraft continues to be in an excellent state of health with all its subsystems functioning normally. Information on the present position of the Cassini spacecraft may be found on the "Present Position" page at: http://saturn.jpl.nasa.gov/mission/presentposition/.

The last Titan flyby, T-85 on July 24, by design put Cassini into a 3:4 orbital resonance with Titan; the spacecraft made three orbits of Saturn while the hazy moon went around four times. That meant the next encounter, T-86, would be more than two months later. While this provided a welcome break for the navigation and spacecraft teams, there has been little relief for the sequencing and science planning teams. The web page describing the Titan T86 flyby, which occurs on September 26, may be found here: http://saturn.jpl.nasa.gov/mission/flybys/titan20120926/.

Wednesday, Sept. 19 (DOY 263)

The Imaging Science Subsystem (ISS) completed a movie of the rings at high phase in order to observe spokes. After a 9-hour Deep Space Network (DSN) tracking period, ISS began another spoke movie.

Thursday, Sept. 20 (DOY 264)

ISS, the Composite Infrared Spectrometer (CIRS), and the Visible and Infrared Mapping Spectrometer (VIMS) performed another observation in the Titan monitoring campaign from a distance of 2.8 million kilometers.

Project management approved an update to the Mission Planning guidelines and constraints, the envelope within which mission activities are designed, developed, implemented, and executed. This was the first major update since Saturn orbit insertion in 2004.

Friday, Sept. 21 (DOY 265)

ISS, CIRS and VIMS observed the F ring for 13 hours.

Saturday, Sept. 22 (DOY 266)

CIRS observed Saturn for 13.5 hours to measure oxygen compounds (H2O, CO2) in the stratosphere. VIMS captured the slow ingress occultation of the star Beta Pegasi as it made a radial pass behind the entire ring system. ISS then began a 6.5-hour movie of the Encke Gap in the outer A ring.

The flight team sent commands today to perform Orbit Trim Maneuver (OTM) 331, which will execute on Sunday.

Sunday, Sept. 23 (DOY 267)

During today's DSN pass, telemetry indicated that the Magnetometer (MAG) Bus Interface Unit had malfunctioned, stopping the instrument's data collection. An anomaly meeting was scheduled for the next day.

Orbit Trim Maneuver (OTM) 331, the Titan T-86 approach maneuver, was performed today using the Reaction Control Subsystem thrusters. The 54-second burn provided a delta-V of about 60 millimeters per second.

ISS took images of known "propeller" features in the rings. Later, ISS made a high-phase observation looking for any possible plumes from Saturn's moon Mimas. The Ultraviolet Imaging Spectrograph (UVIS) then observed an occultation of the star Gamma Pegasi as it passed behind the central A ring where "self-gravity wake" clumping structure is most prominent. The occultation was at an elevation angle where the effects show up most dramatically. More information about self-gravity wakes may be found here: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20070522/

Monday, Sept. 24 (DOY 268)

The flight team participated in an anomaly meeting this morning; realtime commands were approved to power MAG off and back on again.

VIMS observed a radial passage of the Sun behind the rings to further constrain the size distribution of millimeter-sized particles by imaging the "aureole" of forward-scattered sunlight. ISS then observed Enceladus's plumes, and made high-phase observations of dusty rings. Finally, ISS performed a search of the Cassini division between the A and B rings for possible moonlets.

Cassini passed through periapsis going 50,000 kilometers per hour, just inside the orbit of Dione, as illustrated here: http://go.usa.gov/Yc9Q.

Ground processing of ISS and VIMS data by the Instrument Operations team failed because timing errors were present in the data headers due to a DSN problem. A work-around procedure was performed later in the week, which re-enabled processing. No data were lost.

An article by a member of the Realtime Operations team about radio science occultations was published by the NASA Space Place Community Partners at: http://spaceplace.nasa.gov/partners.

Tuesday, Sept. 25 (DOY 269)

Commands were uplinked today to power-cycle MAG. After a round trip light time of 2 hours 58 minutes, the instrument and its BIU were confirmed to be back in a normal state collecting data, which was welcome news on the day before the T-86 Titan flyby.

ISS finished its 13-hour 40-minute Cassini Division moonlet search, after which CIRS performed a 3-hour thermal study of the rings. For four hours, VIMS observed a radial passage of the anti-solar point across the left ansa of the rings, from the F ring to the middle of the D ring, to map out the rings' opposition effect between phase angles of 0 and 1.0 deg. The final part of this observation imaged the left ansa of the rings at a phase angle that matches that of Earth-based observations to provide for cross-calibration between Cassini and terrestrial near-IR spectral observations. An earlier image showing the opposition effect on the rings may be seen here: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2796.

The Attitude and Articulation Control Subsystem team executed two Reaction Wheel Assembly bias maneuvers this week to adjust wheel speeds. Several Cassini scientists are attending the European Planetary Science Congress in Madrid, Spain, this week, and are reporting on various Cassini science results including those on the rings, seasonal variations in the system, and moon-magnetosphere interactions.

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