NASA Cassini Significant Events 11/18/09 – 11/23/09
The most recent spacecraft telemetry was acquired on Nov. 23 from the Deep Space Network tracking complex at Canberra, Australia. 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” page at: http://saturn.jpl.nasa.gov/operations/present-position.cfm.
Wednesday, Nov. 18 (DOY 322)
A news note called “Before Darkness Falls: Cassini to Scan Enceladus on Winter’s Cusp” previewed the upcoming Enceladus flyby, describing it as “A last peek at the intriguing ‘Tiger stripes’ before winter darkness blankets the area for several years.” Scientists are particularly interested in the tiger stripes, which are fissures in the south polar region, because they spew jets of water vapor and other particles hundreds of kilometers from the surface, http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20091119.
A web feature story, “Cassini’s Big Sky: The View from the Center of Our Solar System,” described how Cassini recently helped rewrite our understanding of the shape of our solar system. For decades, scientists pictured our solar system as having a comet-like appearance. The new results suggest a picture more like a bubble. See: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20091120/
The main engine cover was closed on Nov. 18 at the end of the Orbit Trim Maneuver (OTM) #223 backup pass.
Port 2 files were due today as part of the S59 Science Operations Plan process. The files have been merged and a Science Planning assessment of the product released for review.
Both the Live update and Live Update block for the Enceladus 8 flyby were sent up to the spacecraft today along with a tweak to the Magnetometer Subsystem (MAG) Flux Gate Magnetometer (FGM) autorange boundaries.
Thursday, Nov. 19 (DOY 323):
In addition to the Enceladus 8 flyby, science this week included Visual and Infrared Mapping Spectrometer (VIMS) leading a joint Optical Remote Sensing (ORS) E and G ring phase observation and a joint ORS mosaic of Saturn to look at global dynamics. VIMS spent some time looking at Saturn’s northern hemisphere dynamics, and the Composite Infrared Spectrometer (CIRS) performed a helium abundance measurement at the Radio Science (RSS) occultation egress point.
Imaging Science (ISS) acquired data for more Saturn wide-angle camera photopolarimetry and lightning searches, and observed the transit of Pandora across Epimetheus for orbit determination purposes.
The Magnetospheric and Plasma Science (MAPS) teams continued the magnetospheric boundaries campaign and began a campaign to examine interactions between the rings and the satellites.
The Ultraviolet Imaging Spectrograph (UVIS) observed Dione, measuring the satellite’s albedo in ultraviolet light to determine the phase function. This is part of the ongoing campaign to investigate surface microstructure and frost properties as a function of location. CIRS and VIMS rode along.
Friday, Nov. 20 (DOY 324):
A non-targeted flyby of Helene occurred today, and tomorrow along with the Enceladus 8 targeted flyby will be non-targeted flybys of Pandora, Titan, Calypso and Rhea.
On DOY 324 Cassini Radio Science (RSS) successfully completed the orbit 121 Saturn occultation experiment. The experiment was an egress only atmospheric occultation and was covered by Canberra’s DSS-43 for X- and S-band, and DSS-34 for X- and Ka-band. It is the second of a sequence of three occultations in the Cassini Equinox Mission that probe Saturn’s mid-northern latitude, a region which was sparsely sampled during the prime mission. The latitude probed on Rev 121 was about 27.5 deg north as measured near the top of the troposphere. Measurements of the S-, X-, and Ka-band signals’ amplitude, frequency, and phase provide information about the large- and small-scale structure of the atmosphere, the temperature and pressure profile, zonal wind, abundance of microwave absorbing species, the electron number density profile of the ionosphere, and on variability of the profiles with latitude and solar zenith angle.
Saturday, Nov. 21 (DOY 325):
The main engine cover was opened today. This was the 53rd in-flight cycle. The stow position reached a nominal 33.04 degrees.
Just under three weeks after the Enceladus 7 flyby, Cassini once again flew past Enceladus, this time with a very different geometry, approaching within 1,600 kilometers of the surface. E8 closest approach occurred at 2009-325T05:15:03 SCET, at a speed of 7.7 km/sec at 82 degrees S latitude. The spacecraft was under thruster control during the flyby to allow for precise tracking of surface features.
VIMS observed Enceladus as the moon emerged from eclipse, followed by a CIRS fast raster scan of Enceladus’ night side. ISS then took over for high-resolution plume observations obtaining a clear filter mosaic of terrain on the leading hemisphere, providing the best-resolution mosaic so far of that hemisphere. This data can be combined with earlier images of the same region at different geometries to create high-resolution topographic maps, and will be used to look for possible temporal variations in the morphology of the tiger stripes.
CIRS had prime pointing control during closest approach for a high resolution FP3 scan of Baghdad Sulcus – one of the tiger stripe features – tracking along the fissure in the south polar region to examine plume sources and producing the highest-ever-resolution contiguous thermal map of this region.
ISS and VIMS then mapped the sunlit surface of Enceladus on departure. UVIS performed a long stare for a tenuous atmosphere search, which will provide data to associate plume activity with the quantity of volatiles near Enceladus. Over the following downlink of data, RSS performed gravity science to better determine Enceladus’ mass.
Shortly after the targeted Enceladus flyby, Cassini flew less than 25,000 kilometers from Rhea, allowing for ISS high-resolution imaging – around 150-175 m/px – and compositional mapping of regions including the fractured “wispy terrain,” followed by a VIMS point-and-stare observation. UVIS searched for the Rhea ring, targeting beta Ori and kappa Ori. This observation was also used to look for volatiles. Finally, CIRS performed a limb-to-limb fast scan along Rhea’s equator, including night and early morning local times.
To view the flyby page for this encounter link to: http://saturn.jpl.nasa.gov/mission/flybys/enceladus20091121/
Following the flyby this unprocessed image was posted to the Cassini webpage. It shows the ridges and fractures on the surface of the icy moon. Link to: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3749.
In a news note called “Cassini Sends Back Images of Enceladus as Winter Nears,” mission managers said the spacecraft sailed seamlessly through its Enceladus flyby. The spacecraft has sent back temperature data and spectacular images, including ones of the jets of water vapor and other particles emanating from the moon’s south polar region. For the full text and links to additional information go to: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20091121/
Sunday, Nov. 22 (DOY 326):
On Nov. 21, after the E8 flyby, a solid-state power switch (SSPS) trip occurred that turned VIMS off and turned the replacement heater turn on. Real time commands were sent today to turn the instrument and supplemental heater back on and the replacement heater off. This was the first SSPS trip since Nov. 26, 2008. VIMS is currently in a safe state and operating normally.
OTM #224 was performed today. This was the cleanup maneuver from the E8 encounter on Nov 21. The main engine burn began at 2:44 PM PST. Telemetry immediately after the maneuver showed a burn duration of 14.94 seconds, giving a delta-V of 2.54 m/s. All subsystems reported nominal performance after the maneuver.
Monday, Nov. 23 (DOY 327):
The Science Operations Plan process for S60 kicked off today. Two new milestones have been added to this process for prime-rider instrument coordination. The first delivery port for this sequence is scheduled for Dec. 15.
Update: On Tuesday, Nov. 24, images and a movie were released showing the tallest known “northern lights” in the solar system, flickering in shape and brightness high above Saturn. Ultraviolet and infrared instruments on Cassini have captured images of Saturn’s auroras before, but in the latest images, Cassini’s camera was able to capture the northern lights in the visible part of the light spectrum, in higher resolution. This is the first visible-light video of the auroras. The release also features an explanatory video, available at: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20091121/.
