From: Jet Propulsion Laboratory
Posted: Friday, April 19, 2013
The Cassini spacecraft is orbiting Saturn with a 9.6-day period in a plane inclined 61.7 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on April 16 by the 70-meter Deep Space Network station at Goldstone, California. 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/ .
Speeding around periapsis, Cassini dedicated its observations primarily to rings science this week, while commands from the on-board sequence S78 controlled its activities. Back on the home planet, Sequence Implementation Process teams continued working on the ten-week command sequences S79 and S80, which will go active on the flight system in June and August respectively. Also, planning continued for the 2016 start of Cassini's F-ring and Proximal Orbits phase. A Cassini Program representative staffed the NASA booth at the National Science Teachers Association annual conference in San Antonio, Texas, reaching more than 800 teachers.
Wednesday, April 10 (DOY 100)
The Composite Infrared Spectrometer (CIRS) made the first ring observation in a pair that compared temperatures of the north (sunlit) and the south (unlit) sides of the rings under similar observing geometry. Today's observation watched the north side; the corresponding south side observation took place on Friday. The Imaging Science Subsystem (ISS) then created a movie of material revolving through the Encke Gap in the outer A ring, in an effort to monitor the time-variable structure of the Encke Gap ringlets.
Today's news feature describes a study published in Nature this week about electrically charged water molecules from Saturn's D ring showering down into the ionosphere and atmosphere and affecting their electron densities: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20130410/
Thursday, April 11 (DOY 101)
Telemetry indicated that the CIRS Bus Interface Unit (BIU) on the spacecraft had halted, preventing the instrument from receiving commands or returning science results. An anomaly meeting was convened late at night, and commands were created and sent to reset the BIU. Later, telemetry showed that CIRS was operating normally in time to make important upcoming observations around periapsis.
The Visible and Infrared Mapping Spectrometer (VIMS) created a mosaic of Saturn's south pole to study atmospheric dynamics. ISS then reacquired and tracked the orbits of known propellers in the rings (see http://go.usa.gov/YyGR).
The changing seasons on Titan mean radical changes in its atmosphere as described in today's news feature: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20130411/
Friday, April 12 (DOY 102)
The Radio Science team had Cassini turn its high-gain antenna toward Earth, at which time it received a continuous uplink signal that started out an hour and fourteen minutes earlier from the 70-meter diameter Deep Space Network (DSN) antenna in Spain. Using this as a reference frequency, Cassini turned off all telemetry modulation and transmitted pure carrier-signal radio tones at S, X, and Ka-band wavelengths while the spacecraft passed behind Saturn, down at high southern latitude, clear of the rings. On the ground, three DSN stations in Spain and two in California observed the occultation of Saturn's ionosphere and atmosphere until the signals disappeared behind the planet. The Radio Science team will use the data to measure vertical profiles of electron density in the ionosphere, and of density pressure and temperature in the neutral atmosphere. The timing of Cassini's activities was fine-tuned, based on the latest navigation solution, by uplinking realtime commands that shifted a "live moveable block" of commands in the S78 sequence.
After the occultation, the Cosmic Dust Analyzer (CDA) measured particles entering the instrument during ring-plane crossing, to characterize seasonal variation of Saturn's E-ring structure. ISS, CIRS, VIMS and the Ultraviolet Imaging Spectrograph (UVIS) then turned the spacecraft and jointly observed Enceladus's continuously active plume. VIMS made a high-resolution observation of the sunlit side of the rings at high phase illumination to better determine ring particle composition.
Cassini passed through periapsis going 45,220 kilometers per hour relative to Saturn, at about 316,000 kilometers above the cloud tops, just about the distance of Dione's orbit.
Next, CIRS, ISS, and VIMS watched the red-giant star R Doradus as it was occulted by portions of the A and B rings. UVIS then watched the blue star Theta Carinae being occulted by the rings. Last, UVIS mapped the rings to better characterize the ring particles' light-scattering behavior and provide information about particle albedo and composition.
Saturday, April 13 (DOY 103)
ISS, CIRS and VIMS made an observation in the Titan monitoring campaign from 1.8 million kilometers. CIRS performed a radial scan of the rings to further their phase/latitude mapping campaign and assist efforts to model the rings' directional emissivity. VIMS observed an occultation of the infrared-bright star W Hydrae as it made a radial egress pass across almost the entire ring system (due to spacecraft motion, of course). ISS and UVIS then began a high-resolution radial, multicolor scan of the lit face of the main rings, in an attempt to capture data that Cassini was unable to obtain during the Prime and Equinox missions.
Sunday, April 14 (DOY 104)
Today is the birthday of scientist Christiaan Huygens (1629-1695), whose prolific work included the discovery of Titan in 1655. Serendipitously in his honor, ISS, CIRS and VIMS carried out another Titan monitoring campaign observation, now from 2.2 million kilometers away. CIRS, UVIS and VIMS then performed a Saturn observation in an effort to better determine its composition.
Monday, April 15 (DOY 105)
ISS performed an observation in the Satellite Orbit Campaign. It then captured five images of Pluto to provide photometry data to the New Horizons Project, whose spacecraft is on course to fly by the dwarf planet in July 2015. Finally, ISS, CIRS and VIMS made another Titan monitoring campaign observation from 2.3 million kilometers away. The day concluded with VIMS executing calibrations by observing two stars, one after another.
By rotating a near-infrared filter into the instrument's optical path, ISS can peer through the high altitude haze in Saturn's atmosphere to reveal the Jupiter-like stormy weather below, as seen in an image featured today: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4786
Modeling the cycle of hydrocarbons in Titan's atmosphere and in the lakes on the surface is the subject of today's news feature: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20130415/
Tuesday April 16 (DOY 106)
ISS and UVIS observed the very dark irregular moon Siarnaq for 17.5 hours. This body, named after a giant in Inuit mythology, is about 32 kilometers in diameter and orbits 17.5 million kilometers from Saturn.
Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
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