From: Jet Propulsion Laboratory
Posted: Monday, December 1, 2008
The most recent spacecraft telemetry was acquired on Nov. 24 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. 19 (DOY 324):
An image of the unusual aurora over the north pole of Saturn is Astronomy Picture of the Day today. It may be seen at: http://antwrp.gsfc.nasa.gov/apod/ap081119.html.
Only sixteen days after its previous visit, Cassini once again approached Titan for the mission's forty-eighth targeted encounter with that satellite. Closest approach occurred on Wednesday, Nov. 19, at 2008-324T09:17 Pacific Standard Time at an altitude of 1022.6 kilometers above the surface and a speed of 6.3 kilometers per second. The latitude at closest approach was 21.6 degrees S.
TITAN-47 SCIENCE HIGHLIGHTS
For the first time in the Cassini mission, the Visual and Infrared Mapping Spectrometer (VIMS) imaged the Huygens landing site at closest approach with a resolution of better than one kilometer per pixel. It covered areas that have already been observed with RADAR, allowing for a joint study of geological features including dunes and circular features that appear to be either impact craters or volcanic calderas.
During stellar occultations before and after closest approach, VIMS obtained information on atmospheric composition. The Ultraviolet Imaging Spectrograph (UVIS) also observed two stellar occultations, one each of Eta Ursa Majoris and Beta Canis Majoris. These gave vertical profiles of hydrocarbons and aerosols in the high stratosphere and mesosphere, a region that cannot be probed by other instruments.
The Composite Infrared Spectrometer (CIRS) focused on limb sounding of Titan at low latitudes. This observation was designed to measure the spatial variations of trace gas species and isotopic ratios of C, H, N and O, yielding insights into the formation and ongoing evolution of the atmosphere.
The Ion and Neutral Mass Spectrometer (INMS) tried something new for this flyby: riding along with VIMS to measure the dayside ionosphere at low/equatorial southern latitudes. The instrument obtained a good sampling of ions. INMS missed co-rotation, but saw the boundary when Cassini brushed Titan's atmosphere. This is interesting for a variety of reasons. This flyby is the first look at low equatorial southern latitudes. It's also a relatively rare dayside pass.
Imaging Science (ISS) carried out global mapping and photometry of the leading hemisphere, and rode-along with VIMS for global- and regional-scale images. The areas included in the mapping were eastern Xanadu, including Hotei Arcus, the Xanadu-Fensal/Aztlan boundary, and western Tsegihi.
This was a rare Titan encounter for the Magnetospheric Imaging Instrument (MIMI). Its Ion and Neutral Camera field of view remained free of sunlight contamination throughout the pass. This was good for seeing the energetic ion absorption both inbound and outbound. It was also another opportunity for possibly encountering Titan outside the magnetopause.
T47 was a first priority flyby for the Magnetometer Subsystem (MAG). It was a flank-out flyby with a minimum altitude of 1023 km. The geometry of this flyby made it complementary to T46 in the study of the draping of the external magnetic field around Titan by covering the dayside hemisphere. T47 took place in Saturn's near-noon sector at 10.5 hours SLT, where Titan could be found in the magneto sheath if the solar wind pressure was high.
Thursday, Nov. 20 (DOY 325):
The Spacecraft Operations Office (SCO) hosted a Project Review for the fuel-side repressurization activity scheduled for execution in January 2009. This is the last planned repressurization for the Cassini propulsion system.
How many meetings can you pack in to a given day that require the maximum number of people to attend? Here is a sample of a day in the life of engineers and scientists that support sequence development and the operation of a spacecraft. All these meetings were held today, Nov. 20:
Friday, Nov. 21 (DOY 326):
The S48 Science Operations Plan process concluded today with the transfer of all files and products to Uplink Operations. The kick-off meeting for the Science and Sequence Update Process (SSUP) will be held next Tuesday. S48 begins execution on-board the spacecraft on Feb. 17. 2009.
Saturday, Nov. 22 (DOY 327):
Files for maneuver #173 due to execute on Sunday and a real-time Radio and Plasma Wave Science (RPWS) whistler reaction wheel spin down/spin up due to execute over the #173 backup pass on Monday were both sent up to the spacecraft today.
Sunday, Nov. 23 (DOY 328):
Orbit Trim Maneuver (OTM) #173 was performed today. This was the cleanup maneuver from the Titan 47 encounter on Nov. 18. The main engine burn began at 2:45pm PST. Telemetry immediately after the maneuver showed the burn duration was 4.66 seconds, giving a delta-V of 0.77 m/sec. All subsystems reported nominal performance after the maneuver.
Monday, Nov. 24 (DOY 329):
Non-targeted flybys of Helene and Tethys occurred today.
Continuing the Magnetospheric and Plasma Science (MAPS) study of Saturn's auroral regions, the Cassini Plasma Spectrometer (CAPS) started off the day's science by controlling the spacecraft attitude for all of the MAPS instruments. CIRS followed this activity with the first of two observations on this day carefully designed to study how ring temperatures vary from the lit side to the unlit side of the rings. Approaching the rings from above Saturn's north pole, CIRS scanned the rings' unlit side. This was followed by two ISS observations: one to observe Helene during the mission's second-closest flyby of this body, the other to study Saturn's moon Tethys. The CIRS scans of the lit side of the rings that were taken afterwards were meant to be compared with the scans of the unlit side of the rings taken earlier in the day. As Cassini passed through the ring plane, both the Cosmic Dust Analyzer (CDA) and RPWS measured the amount of dust the spacecraft encountered.
Science Planning (SP) has performed an analysis on the post OTM-173 orbit determination solution provided for the DOY 335-339 Live Inertial Vector Propagator (IVP) update. The S46 sequence leads have been informed that an update will probably be required. ISS and CIRS have concurred. The update is now being generated with SCO.
Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
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