From: Jet Propulsion Laboratory
Posted: Friday, February 22, 2013
Cassini is orbiting Saturn with a period of 12 days in a plane inclined 57.1 degrees from the planet's equatorial. The most recent spacecraft tracking and telemetry data were collected on Feb.19 by a 34-meter Deep Space Network station at Canberra, Australia. Except for some science instrument issues described in previous reports, the spacecraft continues to be in an excellent state of health with all of its subsystems operating 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/ .
Cassini is almost continuously acquiring and playing back science data, but when orbiting closely around Saturn, the data taking is rapid-fire and includes many types of observations of rings, atmospheres, satellites, and more. On the heels of the periapsis passage this week came a close encounter with Titan, T-89. Science during this flyby included an important Radio Science gravity field measurement, along with remote sensing and in situ studies of Titan and its environs. The encounter increased Cassini's orbital inclination by another 4.1 degrees to 57.1 degrees, the highest it's been since June of 2009, before equinox on Saturn.
Wednesday, Feb. 13 (DOY 044)
The Imaging Science Subsystem (ISS) observed the D ring at high phase angles for nearly five hours, covering one full orbit of the ring particles. The idea is to monitor time-variable ring structures, including corrugation and structures probably produced by magnetospheric asymmetries. The asymmetries appear to be tied to Saturn's kilometric radiation (named for its wavelength) detected by Cassini's Radio and Plasma Wave Science subsystem.
Taking advantage of the high-phase illumination just before a solar occultation, the Visible and Infrared Mapping Spectrometer (VIMS) made observations of the F ring's right ansa for 5 hours 40 minutes (a typical F ring particle completes its orbit in just under fifteen hours). VIMS then spent the next three hours turned to the main rings. The observing period concluded with an observation of a radial passage of the Sun behind the rings, from the middle of the B ring on out to the F ring. These views help constrain the distribution of millimeter-sized ring particles by imaging the "aureole" of forward-scattered sunlight.
Thursday, Feb. 14 (DOY 045)
With the F ring still in high-phase lighting after the solar occultation, VIMS targeted its left ansa; the rings were almost edge-on by the end of this observation. ISS then took control of spacecraft pointing, and targeted the thin crescent of the small icy moon Enceladus and observed its plumes, lit from behind, for two hours.
ISS executed an azimuthal survey of the "giant propeller" region in the rings between the Encke Gap and the A ring's outer edge. Propellers (see http://go.usa.gov/YyGR) in this region are large and individually tracked as their orbits evolve.
Cassini sped through periapsis at 41,717 kilometers per hour relative to Saturn, having come to within about 388,000 kilometers from the cloud tops.
Friday, Feb. 15 (DOY 046)
The flight team sent commands to the Magnetospheric Imaging Instrument to its adjust high-voltage values in preparation for observations coming up next week by its Ion and Neutral Camera.
VIMS observed an ingress occultation of the bright-infrared star W Hydrae as it made a radial pass behind the entire ring system before going behind Saturn's limb. Then, for nearly eight hours, the Composite Infrared Spectrometer (CIRS) made radial scans of the rings for phase and latitude mapping, to help assimilate models of the rings' directional emissivity.
Saturday, Feb. 16 (DOY 047)
Outbound from Saturn and inbound to Titan, CIRS turned the spacecraft to Saturn's planet-sized satellite to monitor its stratosphere. It repeated the observation on Sunday after the flyby. VIMS participated by observing Titan's illuminated north pole area, monitoring evolution of the polar hood.
Aside from the inbound and outbound CIRS observations, Cassini kept its high-gain antenna squarely facing Earth during the Titan flyby in order to perform a Radio Science experiment for which the Deep Space Network (DSN) had been preparing during the last week. The spacecraft's transponder locked onto an X-band radio-frequency uplink from the DSN, which served as a highly stable frequency reference. On the ground, DSN stations on three continents recorded the Doppler shift in Cassini's X-band and Ka-band downlink signals, which remained phase-coherent with the uplink. This gave the Radio Science team data for characterizing Titan's crust and interior. On the days before and after T-89, the Radio Science team also carried out Titan measurements with the DSN called "Gravity Science Enhancements." More details on the Titan T-89 encounter may be found here: http://saturn.jpl.nasa.gov/mission/flybys/titan20130217/
Sunday, Feb. 17 (DOY 048)
ISS rode along with CIRS's stratosphere monitoring observation, and imaged Titan's surface and atmosphere, including a region where extensive surface changes were observed in the fall of 2010, and an area at mid-southern latitudes on the trailing hemisphere that has only been imaged at lower resolution. Meanwhile VIMS looked for mid-latitude cloud pattern evolution.
Monday, Feb. 18 (DOY 049)
CIRS, with ISS and VIMS riding along, began a 25.5-hour Titan composition science observation. This was part of a series of frequent observations meant to document coincident atmospheric and surface changes.
Cassini continues to reveal a rich variety of phenomena in the fascinating F ring, which is the subject of an image featured today: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4740
Tuesday, Feb. 19 (DOY 050)
An article posted today compares Saturn's magnetic bow shock to a supernova in the way such shocks can accelerate charged particles. It may be seen
Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
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