News | December 18, 2014
Cassini Significant Events 12/10/2014 - 12/16/2014
Cassini is currently orbiting Saturn with a 31.9-day period in a plane inclined 28.6 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Dec. 18 using one of the 34-meter diameter Deep Space Network stations in Australia. The spacecraft continues to be in an excellent state of health with all of its subsystems operating normally except for the instrument issues described at
Information on the present position of the Cassini spacecraft may be found at:
Cassini sped outbound from its Monday periapsis at Saturn, and flew close by the 5,152-kilometer-diameter Titan on Wednesday. The encounter provided another gravity-assist deflection to change the spacecraft's orbit; its inclination decreased from 33.1 to 28.6 degrees from Saturn's equatorial plane, and the orbit's period decreased from 47.8 to 31.9 days. The spacecraft's activities continued to be orchestrated this week by the on-board sequence of timed commands known as S86 -- the S for "Saturn tour" plus a sequential count. One of these activities, on Friday, turned the spacecraft to Earth so it could it receive the S87 sequence and store it on board. Meanwhile back on Earth, development activities proceeded on the ten-week-long command sequences S88 and S89, and planning work continued for the mission's next major accomplishments in 2016 and the 2017 Grand Finale.
Wednesday, Dec. 10 (DOY 344)
Among the benefits of operating a spacecraft in proximity to targets of scientific interest is the ability to use more than one independent means of investigation. Today's T-107 flyby was the second encounter in the Solstice Mission to do so in order to measure Titan's atmospheric density, which is a tricky quantity to determine. Details about today's encounter may be found here:
Inbound to Titan, the Composite Infrared Spectrometer (CIRS) made high-spectral-resolution observations in the far-infrared part of the spectrum to quantify trace chemical species. CIRS, the Imaging Science Subsystem (ISS), the Ultraviolet Imaging Spectrograph (UVIS), and the Visible and Infrared Mapping Spectrometer (VIMS) also covered the hazy moon's surface and atmosphere, at mid-southern latitudes on Titan's sub-Saturnian hemisphere. This was followed by low-resolution remote sensing of the surface and an observation of the vortex high above Titan's south pole, as well as other cloud activity.
With closest approach near the terminator, Cassini's direct-sensing instruments studied the draping and diffusion of the external Saturnian magnetic field within Titan's ionosphere. Realtime tracking by the Deep Space Network (DSN) accompanied closest approach while Cassini probed Titan's atmosphere as described on the web page mentioned above.
Thursday, Dec. 11 (DOY 345)
While rapidly departing Titan, Cassini's telescopes again carried out remote-sensing observations across the spectrum from the ultraviolet through visible light to the infrared. One highlight was an observation by VIMS as it looked for specular reflections -- mirror-like glints of infrared sunlight -- in an area between Titan's lakes Ligeia Mare and Kraken Mare.
Friday, Dec. 12 (DOY 346)
As soon as the spacecraft finished turning to face its high-gain antenna dish to the distant Earth and DSN, it stepped up its downlink telemetry data rate to play back more of the data stored during the T-107 encounter. Then, 90 minutes later, commands from the Cassini flight team finished propagating across the solar system, and for the next 80 minutes the spacecraft received and stored 11,838 individual commands that would comprise the S87 sequence. Then after another 90 minutes, flight team members back home saw confirmation that Cassini had properly received the new sequence, and that it was timed to begin executing on Dec. 17.
Saturday, Dec. 13 (DOY 347)
Flybys of Titan can be expected to introduce some errors in Cassini's trajectory -- especially flybys that are close enough to sweep through the huge moon's upper atmosphere. Now that the Navigation team has had three days' worth of radiometric Doppler and ranging data from the DSN to fit into solutions, commands were created and uplinked to make a correction; Orbit Trim Maneuver (OTM)-398 turned Cassini and fired its small rocket thrusters for 164 seconds. This provided the change in velocity of 160 millimeters per second needed to "clean up" the spacecraft's flight path and ensure that its next encounters and observations will be on the money.
Sunday, Dec. 14 (DOY 348)
ISS turned to stare at the edge of Saturn’s shadow being cast onto the distant, tenuous, highly inclined Phoebe ring.
Today, scientists from the Cassini and Juno Projects held a joint meeting focusing on the interior structures of both Saturn and Jupiter. Experts from both missions, and outside experts, were invited to attend. The meeting was productive and well received.
Monday, Dec. 15 (DOY 349)
ISS began a 39-hour observation of Saturn's irregular moon named Loge, to measure its rotation and its surface properties. This icy object, named for a fire giant from Norse mythology, is only about six kilometers in diameter, and occupies an inclined, retrograde orbit that reaches as far as 23.07 million kilometers from Saturn.
The American Geophysical Union held its fall meeting this week in San Francisco. Over 24,000 scientists and students from around the world attended, presenting papers in fields ranging from climatology to planetary science. This morning, a standing-room-only session entitled "Cassini at Saturn: Science Today and in the Final Three Years" was held, highlighting discoveries and science still to come. There was a related poster session during the afternoon. Dispersed throughout the rest of the week were sessions covering Titan, Enceladus, Saturn's rings, its magnetosphere, and its atmosphere.
A unique image featured today offers a startling comparison of surface brightness between two of Saturn's moons:
Tuesday, Dec. 16 (DOY 350)
As its last event, the S86 command sequence had Cassini turn to face Earth for an eight-hour communications and tracking session. S87 will take control next.
During the past week, the DSN communicated with and tracked Cassini on seven occasions, using stations in Australia and California. A total of 11,977 individual commands were uplinked, and about 1200 megabytes of telemetry data were downlinked and captured at rates as high as 110,601 bits per second.