A high point of the week was actually on the ground as two European Space Agency (ESA) 35-meter diameter Deep Space Antennas (DSAs) tracked Cassini. The Cassini Project will be depending on ESA’s DSAs to fill in important gaps in the execution of crucial Radio Science observations during Cassini's 22 Proximal Orbits next year.
At Saturn, Cassini followed another orbit just like its previous one, speeding around the ringed planet in 9.6 days. As this week began the spacecraft coasted inward along the slanted plane of its orbit, having passed the high point of its "roller-coaster ride" the day before. The spacecraft sped southward through the ring plane on Sunday, close enough to Saturn for it to cross through the vast, dusty E ring. Going northward again, Cassini then passed the orbit of Saturn's planet-like moon Titan on Tuesday, on its way out to another apoapsis two days later. While Cassini's path was the same as last week's, this week's views of Saturn, the moons, and its ever-changing system of rings were fresh and new.
Wednesday, Oct. 19 (DOY 293)
The only science activity today was a calibration. The Magnetometer (MAG) had the spacecraft slowly pitching about its lateral X axis for eight hours, as if tumbling head-over-heels. (All Cassini's instruments undergo regular calibrations, though they are seldom mentioned in this report.)
Thursday, Oct. 20 (DOY 294)
The Imaging Science Subsystem (ISS) and the Visible and Infrared Mapping Spectrometer (VIMS) made a two-minute storm-watch observation on Saturn. Next, ISS spent an hour looking for small objects near the planet. This satellite-orbit-campaign observation repeated on Friday for 110 minutes.
The bright red star Lambda Velorum happened to make a long pass behind the outer parts of Saturn's rings, from Cassini's point of view. VIMS took the reins and tracked the star for 2.4 hours performing an instrument calibration before the star was occulted. The instrument then spent 5.25 hours observing while Saturn's rings proceeded to occult the star; ISS and the Composite Infrared Spectrometer (CIRS) rode along. This illustration of the viewing geometry catches the star as it was passing behind the A ring's Encke Gap.
When the stellar-occultation observation was done, CIRS spent six hours measuring the rings' temperatures. The Ultraviolet Imaging Spectrograph (UVIS) rode along.
Today's news feature is about the changes that Cassini has been observing on Titan: /news/12951/cassini-sees-dramatic-seasonal-changes-on-titan .
Friday, Oct. 21 (DOY 295)
As soon as ISS and VIMS finished another two-minute Saturn storm-watch observation, CIRS studied the rings again for five hours. UVIS rode along, as it did when ISS led the next activity, spending five hours making color images of the main ring system.
A number of Cassini scientists participated in the American Astronomical Society's Division for Planetary Sciences and the European Planetary Science Congress, which were held in Pasadena, California. The six days of meetings wrapped up today with a press briefing on next year's Cassini Grand Finale.
Saturn's northern region has been changing its appearance as summer approaches in that hemisphere, as evident in this pair of images: /resources/17539 .
Saturday, Oct. 22 (DOY 296)
Cassini took the opportunity today and during the following day to carry out multi-spectral observations of Saturn's mid- to large-sized icy satellites, ranging in length from one hour to over eight hours. Among the targets were the small but geologically active Enceladus, the large, bright Rhea, streaked Dione, heavily-cratered Tethys, and the little moon Mimas with its giant impact crater. All of the optical remote-sensing (ORS) instruments, each with its own powerful telescope, participated; ISS used its filter wheel and multiple exposures to record some full-color images. These observations provided mainly north-polar and mid-latitude coverage of terrains that had been poorly illuminated, or not illuminated at all, earlier in the mission.
There were no observations of huge Titan this week, though it is never forgotten; three more close, targeted encounters with that planet-like object remain in the mission.
Cassini's ORS observations of moons were interrupted when the bright blue star Zeta Centauri made a radial pass behind Saturn's entire ring system. UVIS led this occultation observation for 5.6 hours, with CIRS riding along. It provided rare measurements of structure in the C ring. Data from this occultation will help scientists understand the long-term variability of small-scale structures throughout the ring system, as well as particle size distributions, clumps, and the evolution of waves in the rings.
Sunday, Oct. 23 (DOY 297)
Cassini swept through periapsis, the closest point to Saturn, in its Orbit #246 today; its speed and distance were similar to those on October 13.
The timing of CIRS's three-hour observation of Saturn's rings today was chosen so that the observation geometry would mirror that of its observation back on Oct. 20. The phase and elevation angles of the rings were similar, but today's observation was looking at the dark side. By comparing the observations, CIRS scientists hope to constrain how thermal energy is transported between the sunlit and unlit sides of the rings, which in turn has implications for the overall dynamics of Saturn's ring particles. UVIS and VIMS participated.
Today's ISS-led study of Dione built on several lines of evidence that the big icy moon might be currently exhibiting a low level of geologic activity. The ORS instruments spent 3.75 hours looking for any sign of plumes, at high-phase angles of sunlight, when any such plumes would be backlit.
Another CIRS-led ORS observation searched for thermal anomalies on Saturn's moon Rhea for eight hours, to derive the object's thermal inertia.
Monday, Oct. 24 (DOY 298)
The spacecraft remained Earth-pointed today while the Magnetospheric and Plasma Science (MAPS) instruments continued to collect data.
Saturn's clouds and fluid dynamics -- how do they relate? Today's featured image highlights the question: /resources/17538 .
Two of the European Space Agency's (ESA) 35-meter diameter antennas tracked Cassini today, from stations in Malargüe, Argentina, and New Norcia, Australia. Both stations demonstrated their ability to transmit a frequency-reference uplink signal to Cassini. This will allow coherent tracking of Cassini that the project will be depending on to execute crucial Radio Science observations during the 22 Proximal Orbits next year.
Tuesday, Oct. 25 (DOY 299)
ISS started a 31-hour observing run trained on Saturn's irregular moon Erriapus. Named for a giant in Gaulish mythology, Erriapus is only about eight kilometers in diameter. It has a very dark surface, and in its inclined orbit, it reaches as far as 25.6 million km from Saturn.
The Deep Space Network (DSN) communicated with and tracked Cassini eight times this week, using stations in Spain, Australia and California. A total of 28 individual commands were uplinked, and about 1,244 megabytes of telemetry data were downlinked and captured at rates as high as 110,601 bits per second.
Cassini is orbiting Saturn with a period of 9.6 days in a plane inclined 57.9 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on October 26, using one of the 34-meter diameter DSN stations in California. 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 http://saturn.jpl.nasa.gov/anomalies .
This week's feature article is on Enceladus: https://saturn.jpl.nasa.gov/science/enceladus .
Cassini's path up to mid-day Oct. 25 is illustrated here: http://go.nasa.gov/2cEsImH . At that time, the countdown clock in Mission Control was showing 324 days until the end of the mission.
Milestones spanning the whole orbital tour are listed here: https://saturn.jpl.nasa.gov/mission/saturn-tour/tour-dates .
Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at: