From: Jet Propulsion Laboratory
Posted: Saturday, January 3, 2009
The most recent spacecraft telemetry was acquired on Dec. 22 from the Deep Space Network tracking complexes at Goldstone, California, and 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, December 17 (DOY 352):
Orbit Trim Maneuver (OTM) #178 was performed today. This is the approach maneuver setting up for the Titan 49 encounter on Dec. 21. The reaction control subsystem burn began at 1:15 PM PST. Telemetry immediately after the maneuver showed the burn duration to be 19.63 seconds, giving a delta-V of 0.027 m/sec. All subsystems reported nominal performance after the maneuver.
All of the Optical Remote Sensing (ORS) instruments observed Rhea today from a distance of 770,000 km at phase angles increasing to 165 degrees. RADAR was in a passive detection mode to observe radiation originating from the atmosphere of Saturn below the visible clouds and haze. This radiation is modulated by ammonia in the atmosphere. Mapping the polar regions gives scientists insight into the behavior of the north polar hexagon and south polar vortex at deeper pressure levels. Tomorrow, RADAR will perform similar observations over the south polar region, with the Visual and Infrared Mapping Spectrometer (VIMS) performing a polar dynamics study. The poles are experiencing changes in seasonal lighting, with the north polar region experiencing sunlight for the first time in over a decade and the south polar region about to enter over a decade of polar winter. VIMS studies of these regions over the next few years hope to reveal changes in Saturn's meteorology and circulation produced by such seasonal changes, including solar heat deposition.
Friday, December 19 (DOY 354):
The Composite Infrared Spectrometer (CIRS) mapped the thermal structure of Saturnís upper troposphere in the far infrared. Data for these maps are taken at different times during the mission to reveal seasonal and other temporal variations. In order to cover two full rotations of Saturn, 22 hours were devoted to this activity.
Sunday, December 21 (DOY 356):
On Dec. 21, Cassini flew by Titan at an altitude of 970 km, and a speed of 6.3 km/sec. Closest approach occurred at approximately 6:15 AM PST, latitude 43.9 degrees south. Titan 49 is the last targeted flyby of 2008. The next will be Titan 50 on Feb. 7, 2009.
Titan closest approach found RADAR in control of spacecraft pointing to perform altimetry observations across Ontario Lacus. This is the first time in the mission that RADAR has obtained altimetry data across a known or suspected lake. The topography profile will help scientists understand the slopes driving drainage into Ontario as well as providing evidence about whether it is presently liquid-filled. RADAR also captured a Synthetic Aperture Radar swath of the almost completely unmapped southwestern quadrant of Titan, as well as the south polar terrain.
The Ion and Neutral Mass Spectrometer (INMS) rode along with RADAR during a relatively rare wake side pass. INMS obtained good measurements of non-reactive neutrals, and limited coverage of the ionosphere near closest approach.
Imaging Science (ISS) acquired global and regional mapping mosaics of Titanís leading hemisphere at mid-southern latitudes and rode along with VIMS to acquire high-resolution coverage at higher southern latitudes. VIMS acquired mid-resolution and high resolution spectra south of Xanadu, pointed to the Hotei region to acquire a 2x2 mosaic at 10 km/pixel of this 5 micron bright region, then mapped a part of the southern hemisphere - at 5 km/pixel - that has never previously been mapped.
CIRS continued to extend spatial and temporal coverage of Titan, performing most major observational activity types. These included global temperature mapping, vertical profiles of minor gas species in the mid-infrared, and global mapping of far-infrared trace species such as CO, H2O and HCN.
The Magnetospheric Imaging Instrument (MIMI) measured energetic ion and electron energy input to Titanís atmosphere.
T49 was an upstream flank-out flyby with a minimum altitude of 970 km. For the Magnetometer Subsystem (MAG) the geometry of this flyby was suitable to study the magnetic pileup region and the balance between the magnetic pressure in the magnetic barrier and the thermal pressure in the ionosphere. T49 took place in Saturn's near-noon sector where Titan could be found in the magneto sheath if the solar wind pressure was high.
Finally, the Radio and Plasma Wave Science (RPWS) instrument measured thermal plasmas in Titan's ionosphere and surrounding environment, searched for lightning in Titan's atmosphere, and investigated the interaction of Titan with Saturn's magnetosphere.
Here is the link for the flyby web page: http://saturn.jpl.nasa.gov/mission/flybys/titan20081221/
Monday, December 22 (DOY 357):
A beautiful close-up image of the surface of Enceladus is Astronomy Picture of the Day today. Check it out at: http://antwrp.gsfc.nasa.gov/apod/ap081222.html
As Saturn goes around the sun, once every 14 to 15 years it turns its rings edge-on to Earth. Because the rings are so thin, they can actually disappear when viewed through a backyard telescope. The best time to look is now. The 0.8-degree opening angle of Christmas 2008 is the minimum for some time to come. In January 2009 the rings begin to open up again, a temporary reversal caused by the relative orbital motions of Earth and Saturn. By the time narrowing resumes in summer 2009, Saturn's position in the sky will be approaching the sun, so looking at it through a telescope then could actually be dangerous. The next ring plane crossing that's easy to watch won't come until 2038. For the full story link to: http://science.nasa.gov/headlines/y2008/22dec_crazytilt.htm
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